• Volume 35,Issue 3,2013 Table of Contents
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    • Earthquake Damage Characteristics of the Minxian-Zhangxian M_S6.6 Earthquake and Its Lessons

      2013, 35(3):401-412.

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      Abstract:According to scientific investigation of the seismogenic structure,housing and the lifeline engineering damages and the secondary geological disasters induced by the Minxian-Zhangxian MS6.6 earthquake on July 22,2013,that the characteristics of seismogenic structure and seismic intensity distribution,damage characteristics and failure mechanism of houses in different intensity zones are introduced.Moreover,a thorough analysis of typical loess landslides are carried out,the damage characteristics of fault effects,amplification effects of mountain and slope effects are summarized as well.Based on the in-depth investigation of seismogenic structure,site conditions of the quake-hit areas,different houses damages and secondary geological disasters,some lessons have been proposed for reconstruction of the quake and seismic fortification in the future.

    • Analysis of Trigger Factors of the Minxian-Zhangxian M_S6.6 Earthquake Occurrence Date and Short-impending Prediction Methods

      2013, 35(3):413-418.

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      Abstract:Statistics of earthquake occurrence dates predicted for many years by Chinese earthquake researchers indicate that earthquakes often occur on the dates of solar terms,displacement of geomagnetic low points,and the first and the fifteenth days of lunar months,which agree well with earthquake statistics. Twenty-four points were set during a one-year period on the basis of sun position.Each point is referred to as a solar term,which generally refers to the day it was recorded. The value of the strength of the magnetic field in a direction perpendicular to the ground (Component Z)was generally lowest at 12:00each day but occasionally occurred before or after that time.In such instances,the low point is said to be"displaced" ." Quiet day" is a technical term that refers to daily changes.Thus,lowest points occurring at times other than 12:00are noted by"displacement of low point of Component Z on quiet day" .Displacements of low points at certain times measured by all magnetic observatories are marked on a map as postponed in some regions for 2hor 4hor are indicated as not postponed.These displacements are demarcated by adisplacement line of low point,in the vicinity of which earthquakes often occur.Dangerous earthquake generation generally occurs 27and 41days(±4days)following formation of the displacement line.Syzygy occurs when the Earth,Sun,and Moon are in a straight line.The first day of the lunar month occurs when the Moon circumambulates between the Sun and the Earth,and the dark face of the Moon is directed toward the Earth.The fifteen or the sixteenth day of the lunar month occurs when the Moon circumambulates back to the Earth,and the hemisphere illuminated by the Sun faces the Earth.The sevenfold and ninefold rules in various years are indices used in impending earthquake prediction that were proposed by the author in 1986.We determined that if strong earthquakes of different years occur in a certain region during the same or similar seasons,the interval of their occurrence dates was a multiple of seven or nine days.This time interval characteristic of sevenfold and ninefold rules in different years enables accurate prediction of the dates of future strong earthquakes in particular regions based on the historical dates of strong earthquakes in the same area.In this study,the July 22,2013,occurrence date of the Minxian-Zhangxian MS6.6earthquake is analyzed on the basis of such triggering factors,and a number of concepts and methods of short-impending prediction are presented on the basis of these phenomena.

    • Study on Seismogenic Structure of 2013 Minxian-Zhangxian M_S6.6 Earthquake with Seismological Data

      2013, 35(3):419-424.

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      Abstract:Velocity and Qvalue tomography,in addition to precise positioning methods of small earthquakes,were used to obtain the deep structure of seismic source area and spatial distribution images of aftershocks.The data of velocity and Qvalue imaging consist of two parts.The first includes the observation data from a high-density portable seismic array consisting of 150 stations with a reporting period of November 2009 to November 2011 in the area of 32.2-36°N,102.8-107.1°E.The second includes data from a fixed network during the period of 1970-2010.From these datasets,we selected 6 334seismic events recorded by at least 8stations and conducted velocity and Qvalue inversion calculation.We applied the three-dimensional grid search method to aftershock relocation,in which 746seismic events met with S-P arrival time differences detected by at least three stations.Finally,we obtained the relocation results of 400seismic events,and we applied the same method to relocation of the Minxian MS5.2earthquake occurring on November 13,2003,and the Minxian-Zhuoni MS5.0earthquake occurring on September 7,2004.We set the P1profile perpendicular to the direction to research in the deep distribution of the seismogenic fault.The profile P1crosscut the Lintan-Tanchang fault and the Minxian-Zhangxian seismic source area.We obtained the velocity profile,Q value profile,and aftershock distribution,which were combined with the focal mechanism solutions of these three earthquakes and the distribution of smaller earthquakes recorded since instrumental record have been kept.The results show that the seismogenic fault of Minxian-Zhangxian MS6.6earthquake is a buried fault with a NW strike direction,SW dip direction,and a dip angle steeper in the shallow region.In addition,the fault is thrust and sinistral strike-slip,and its exposure at the surface is 20km from Minxian section of the Lintan-Tanchang fault.The seismogenic fault and the Minxian section of the Lintan-Tanchang fault may have met at a deep level to form a fault zone to the south with a NW dip direction.The seismogenic faults of the Minxian MS5.2,Minxian-Zhuoni MS5.0,and Minxian-Zhangxian MS6.6earthquakes may belong to the same fault.The seismogenic fault of the Minxian-Zhangxian MS6.6earthquake is located in the suture parts of two secondary blocks.The east block is relatively stable,and the west block moves eastward and is blocked by the east block to form the extrusion area.The Qvalue of the extrusion area is lower and shows velocity uplift.In the Earth's crust of the west block,the Qvalue is lower,which provides eastward movement of west block with more favorable conditions.The occurrence region for earthquakes of MS≥5has included three events since 2003with seismogenic faults at least 20km from the Lintan-Tanchang fault;the dip direction is contrary.The seismogenic fault is located in the southwestern edge of Zhangxian's southern block,which is a secondary block(triangle)with a stable internal region.Three strong earthquakes occurred in western boundary of this block,which is conducive to the strain energy accumulation of the eastern region and the northern edge,which is the north rim fracture of western Qinling.The eastern region and northern boundary will likely be main regions of seismic activity of the southeast area of Gansu for the next several years.

    • Moment Tensor Inversion and Seismogenic Tectonics of the 2013 Minxian M_S6.6 Earthquake in Gansu

      2013, 35(3):425-431.

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      Abstract:On July 22,2013,the Minxian magnitude 6.6 earthquake occurred beneath the northeast margin of the Tibetan plateau,Gansu,China.The earthquake and its aftershocks caused considerable damages,including more than 95 casualties,2414injuries,and approximately 17.5billion yuan in property damage.More information on the source properties of such events can help to characterize fault the structures,which can contribute to an improved understanding of the hazards associated with future great earthquakes.As of August 28,13:35,aftershocks have been recorded by the Gansu seismology network,including a magnitude 5.6event following the mainshock.We analyzed the broadband waveforms for the mainshock with sufficient signal-tonoise levels to invert for seismic moment tensors.All stations involved in this study are broadband stations situated near the July 22mainshock;data showing such problems as misorientation of horizontal components,mislabeling,and polarity reversal in one or more components(Niu et al.,2010)were removed.During the data processing,we removed the mean value and instrument response,detrended the waveforms,integrated the three-component velocity waveforms to displacement,and rotated the horizontal components to the radial and tangential directions.Before performing moment tensor inversion,waveforms were filtered with a Butterworth filter with frequencies between 0.016Hz and 0.05Hz.On the basis of the Crust 2.0global crustal model,and considering the heterogeneity of the crust and the distances to the recording stations,various velocity models for each station were employed to account for variabilities in the crustal structure.To insure the quality of the results of the inversion process,we retained only the station with variance reduction(VR)is≥80,and got 6stations for the inversion.After depth iteration,the best solutions obtained at a depth of 8km were 87,13,and 93for double couple(DC),the compensated linear vector dipole(CLVD)component,and VR,respectively,which indicates highquality results.The two panel's strike,dip,and rake of the solution were 195°,54°,and 149°and 305°,65°,and 40°respectively.The moment tensor solutions showed considerable reverse features and contained part of the strike-slip component.Geologic survey indicated no surface rupture.Regarding tectonic framework and the aftershock distribution features,our inversion results were essentially consistent with the strike of the Lintan-Tanchang fault,and the aftershock distribution occurred near the fault.This phenomenon indicates that the Lintan-Tanchang fault was the main tectonic trigger for the Minxian magnitude 6.6earthquake and that the seismogenic fault of the earthquake was a subfault of the Lintan-Tanchang fault.

    • Analysis of the Focal Mechanism and Tectonic Stress of Minxian M_S6.6 Earthquake

      2013, 35(3):432-437.

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      Abstract:The Minxian MS 6.6 earthquake,the largest destructive earthquake to affect Gansu province,occurred on July 22,2013.Its epicenter at N34.54°,E104.21°was located between the northern fringe fault of western segment of Qinling Mountain and the Lintan-Tanchang fault. After the earthquake occurred,we solved the focal mechanism of the main shock with P wave polarity from the waveforms obtained from the Gansu province seismic network.We then compared the solution with the focal mechanisms published by Harvard and the United States Geological Survey(USGS).During the 10years prior to the Minxian earthquake,several earthquakes stronger than Mb 4.5occurred in this region.We solved the focal mechanisms of these earthquakes with P wave polarity data,and we compared the focal mechanisms with those of the Minxian earthquake.Similar morphologies were revealed,and each contained a larger thrust component.The focal mechanism of a small earthquake is more difficult to solve than that of a large earthquake.However,because small earthquakes occur more often than large earthquakes,it is desirable to refer to the tectonic stress by the focal mechanisms of multiple small earthquakes to decrease the effects of local structures and to highlight the features of the region tectonic stress.Previous methods used to determine tectonic stress from multiple focal mechanisms include grid search.However,because the smallest search grid is 5°,the search grid was too large to meet the exact solution of the tectonic stress.Other methods ignore the data accuracy or cannot give the error of parameters.The newest method obtains the optimal solution of tectonic stress using finer grid parameters of 1°×1°and gives the error of parameters.In this paper,we solve the tectonic stress using this method.A broadband mobile seismometer observation array was conducted in southeastern Gansu in 2010-2011,in which abundant near shock waveforms were obtained.We examined small earthquakes in close proximity to the Lintan-Tanchang fault,which was the triggering seismic fault of the Minxian earthquake,at a distance of less than 50km.To maintain the reasonableness of the focal mechanism,after identifying the P wave polarity of selected earthquakes,we identified 31earthquakes in which the P wave polarity was more than 9and had a good envelope to the source.We solved their focal mechanisms,which we used to solve the tectonic stress in this region.The results show that the direction of the main pressure was 70.12°,which is very close to the results of previous studies.The main pressure was NEE in this region because of the combined action of the Qinghai-Tibetan Plateau,Ordos,and South China blocks.After the Minxian earthquake,a series of aftershocks occurred,from which and we expect to obtain additional data for analyzing the changes of tectonic stress.

    • Calculation of the Focal Depth of M>4.0 Earthquakes in Minxian,Gansu,Based on sPn Seismic Phases

      2013, 35(3):438-442.

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      Abstract:Earthquake focal depth is an important parameter for research on seismology,the structural study of earthquakes,seismic hazard assessment,and earthquake event recognition.As a basic seismic parameter of time and space,earthquake focal depth affecting the size of the earthquake disaster and is one of the most difficult parameters to measure accurately because its determination is related to source process fault structures and stress fields.Stations layouts are sparse in our country;therefore,the velocity model generally used to determine earthquake focal depth.The China Earthquake Networks Center detected a magnitude 6.6earthquake in Dingxi City,Gansu Province,on July 22,2013,at 7:45Beijing time in the border area between Minxian and Zhangxian with a focal depth of approximately 20km.The epicenter was approximately 15km from Minxian,45km from Zhangxian,120km from Dingxi City,and 170km from Lanzhou City.As of July 30,2013,1066aftershocks were recorded,nine of which were greater than magnitude 3.0.According to the analysis,the seismic phases of three M>4.0earthquakes occurred in Gansu Minxian in July 2013.The Sichan digital seismograph network recorded relatively clear sPn seismic phases of more than 250km in the area near the epicenter.In this study,sPn and Pn seismic phase methods were used to calculate the seismic depth.The focal depths of the three Minxian earthquakes were recalculated to obtain a more accurate earthquake focal depth.The earthquake focal depth is an important focal shock parameter.Because the method of using more than one pair of sPn and Pn seismic phases to calculate the seismic depth was adopted in this study,the main error source is the seismic phase and the Earth's crust model error;therefore,identification of sPn and Pn is crucial.By recalculating the focal depth of the three Minxian M >4.0earthquakes,it is concluded that focal depth of the M6.6principal earthquake was 15.4km,the focal depth of the M 5.6aftershock was 9.6km,and the focal depth of the M4.1aftershock was 9.2km.The focal depth of the two aftershocks is obvious shallow;these results show that the rupture process of the M 6.6principal earthquake was from deep to shallow regions.An accurate focal depth was obtained by deep seismic phases to provide basic data for earthquake prediction and earthquake hazard analysis.

    • Relocation of Mainshock and Aftershocks of the 2013 Minxian-Zhangxian M_S6.6 Earthquake in Gansu

      2013, 35(3):443-447.

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      Abstract:A 3-D velocity model of the southeast Gansu Province region,including the 3-D grid searching algorithm and double difference method,was used to examine the relocation the Minxian-Zhangxian MS6.6 earthquake occurring on July 22,2013,and its aftershocks from July 22to July 25.The grid search method was used to determine earthquake location and the S-P arrival time of 400seismic events,which agreed with data detected by at least three stations.Of these events,336were used to calculate double-difference location,and 261were used to obtain the relocation results.After relocation,the average estimation errors of the source location were 1498m in the E-W direction,1385.2min the N-S direction,and 2 492.3min the vertical direction.On the basis of these calculation results,the seismogenic structure was compared with the data of geological structure,and the results showed that the mainshock was relocated to 34.54°N,104.189°E,with a focal depth of 13.5km.The aftershocks were distributed mainly between the Lintan-Tanchang fault and the northern edge of the West Qinling fault;several were distributed in the southwestern region of the Lintan fault.The distribution of the aftershocks was in the NW or NWW direction,which is essentially consistent with the strike of Lintan-Tanchang fault,although the dominant distribution was not obvious.Therefore,we examined the A-A′profile perpendicular to the direction to research the relationship between the distribution of earthquakes and fracture structure and determined that this profile crosscuts the Lintan-Tanchang fault.We obtained similar results using the 3-D grid searching algorithm and the double difference method, which revealed that the focus depths are mainly distributed in 0~10km before relocation,and the average depth was 6km.In contrast,the focus depths of the aftershocks were distributed mainly in 5~20km after relocation,which indicates that the aftershock sequence occurred mainly in the upper and lower crust.The distribution of the earthquake was in the SW direction,thus,we speculate that the dip direction of the seismogenic fault was SW,and the deep distribution is deeper.The focus depths determined by the 3-D grid-searching algorithm can reach to 25km,whereas those determined by the double difference method were deeper at a maximum of 30km.The Lintan-Tanchang fault,with a NW-NWW strike and a SW dip of 50°-70°,is in closest proximity to the earthquake swarm and is located between the East Kunlun fault and the northern edge of West Qinling fault.The transition fracture of the structural change and the geologic structure of the transition zone are complex and provide the regional geological background.The seismic profile A-A′shows that the basic characteristics of the seismogenic fault,with a SW dip direction,differ from those of the Lintan-Tanchang fault such that their exposures at the surface are 20km apart.Therefore,we believe that Fault F3is a seismogenic fault.However,other characteristics of Fault F3are unclear and need to be developed through active fault detection research.

    • Characteristics of Crustal Structures in Source Area of the Minxian-Zhangxian M_S6.6 Earthquake

      2013, 35(3):448-454.

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      Abstract:An MS6.6 earthquake occurred at the junction of Minxian and Zhangxian on July 22,2013,at 7:45in the northern section of the North-South seismic zone in the southeast region of Gansu Province.This area is a moderate-strong earthquake-prone region in which the Minxian MS5.2 earthquake and Minxian-Zhuoni MS5.0 earthquake also occurred in 2003and 2004,respectively.In this study,we analyze teleseismic data recorded in 2008-2009 by Minxian station,which is the permanent station in closest proximity to the Minxian-Zhangxian earthquake.Receiver functions aligned by azimuth indicate obvious heterogeneity beneath the Minxian station;observed receiver functions of Minxian station vary according to azimuth.That is,receiver functions of the seismic source area and adjacent areas show obvious differences.In the seismic source area,the receiver function is clearly apositive signal of approximately 1.5s,which indicates that a high velocity zone is present in the middle-lower crust.In the adjacent areas,the receiver function is clearly a negative signal of approximately 1.5s,indicating the presence of a lower velocity zone in the middle-lower crust.This phenomenon shows obvious crustal structure differences between the seismic source area and adjacent areas.In addition,we used the H-kstacking method of receiver functions to determine the crustal thickness and wave velocity ratio of the two areas.The results show crust thicknesses of 45km and 47km and wave velocity ratios of 1.76and 1.69 in the source area and adjacent area,respectively.Therefore,obvious differences in crustal velocity structure appear between the two areas.In the seismic source area,the Ps,PpSs/PsPs clearly indicates crustal discontinuity.Therefore,the H-k stacking method of receiver functions was used to determine the depth of the discontinuity surface and the wave ratio velocity.The H-k stacking results showed an upper crustal thickness of 15km and a wave velocity ratio of 1.62.We estimated the middle-lower crustal thickness and wave velocity ratio to be 30km and 1.84,respectively.Therefore,the soft middle-lower crust is covered by the hard upper crust at the top in the source area.This type of small-scale material inhomogeneity may be an important part of the deep structure of the Minxian-Zhangxian earthquake background.We estimate that the rupture of the Minxian-Zhangxian earthquake may have been attributed to lower crustal flow leading to rupture of the upper crust.

    • Analysis of the Growth Phenomenon of Seismic Correlation Length Prior to Minxian-Zhangxian Earthquake

      2013, 35(3):455-458.

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      Abstract:The seismic correlation lengths prior to the Minxian-Zhangxian earthquake occurring on July 22,2013,have been studied using the single-link cluster analysis(SLC)method.The catalogs used were downloaded from the China Earthquake Data Center(CEDC;http://data.earthquake.cn/data/).Earthquakes that occurred during the five years prior to the main shock until its origin time were located in an area centered on the main shock(34.5N°,104.11°E)with a range of 32°~37°,102°~107°.We selected 2.5(ML)as the minimum magnitude and verified the completeness of the catalogs prior to the mainshock using the Gudengberg formula,which showed good results above magnitude ML=2.5.The result shows that an increase in correlation length for moderate-sized earthquakes was observed nearly 1.5years before the main shock and can be fitted well by the power law.For the preparation and occurrence stage of the earthquake process characterized as a self-organized critical phenomenon,direct testing for the increase in spatial correlation lengths prior to large earthquakes is an independent approach used to detect critical point behavior in observed seismicity.The results of this study show that the self-organized critical point characteristic was been observed prior to the Minxian-Zhangxian MS6.6earthquake.The results from the many earthquake applied to systematically extract a region of increased correlation length from a dataset.Estimates for the epicenter of an expected mainshock may be then obtained from the results of the grid search.

    • Focal Mechanism of the Minxian-Zhangxian M_S6.6 Earthquake

      2013, 35(3):459-462.

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      Abstract:The Chinese seismological station net determined that an MS6.6 earthquake occurred on July 22,2013,at 7:45CST at the border of Minxian and Zhangxian counties in Gansu Province. By the end of August 26,1300aftershocks had occurred in the seismic region of the main earthquake,including one of 5.0~5.9level,one of 4.0~4.9level,and nine of 3.0~3.9level.The largest,with magnitude of 5.6,occurred at 9:12on July 22.This earthquake caused heavy casualties and economic losses. In this study,the cut-and-paste(CAP) method was used to determine that the earthquake was thrust and strike-slip,MWwas 6.1,and the focal depth was 7km.The nodal plane II parameters of the best double-couple are strike 304°,dip 64°,and rake 44°.The strike of the nodal plane had the same trend as that of the Lintan-Tanchang fault,and the characteristic of dip and slip represent left lateral slip,which also corresponds to the Lintan-Tanchang fault.The nodal plane is representative of the seismogenic fault plane.Therefore,the Minxian-Zhangxian Ms6.6earthquake is in osculating correlation with activity of the Lintan-Tanchang fault.

    • Focal Mechanism of the Wenxian M_S4.5 Earthquake on July 27,2013

      2013, 35(3):463-464.

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      Abstract:

    • Effects of Aftershocks on Quick Determination of Hard-hit Area for Emergency Rescue after the Minxian-Zhangxian M_S6.6 Earthquake

      2013, 35(3):465-470.

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      Abstract:Information used to evaluate disaster conditions shortly after an earthquake is very limited.To develop fast earthquake emergency response and rescue techniques using aftershock information that can quickly be accessed,the location relationship between the spatial distribution of aftershock activity in different time periods and heavy disaster area of intensity distribution is analyzed by actual investigation after an earthquake.Moreover,considering the influence factors of the seismogenic fault strike,residential area density,landform,and physiognomy in seismic area,the optimum time point of aftershocks statistics can reflect severe disaster areas.To quickly evaluate the severity of disaster areas according to the distribution of aftershocks at the optimum time point with consideration of other influencing factors after earthquakes,improvements can be made in services provided for earthquake emergency rescue.It was determined that the most severe damages occur 3hafter aftershock distribution,and earthquake landform and rainfall disaster damage occur along the direction of aftershock distribution.When a severe disaster area is determined by the aftershock distribution range,adjustments of the long axis direction should be made in reference to the seismogenic fault strike;the direction of the long axis is generally consistent with seismogenic fault direction.Disaster severity is adjusted on the basis of settlement distribution.Therefore,comprehensive analysis of the influence of various factors causing the disaster is necessary for disaster mitigation.

    • Study of the Characteristics and Inducing Mechanism of Typical Earthquake Landslidesof the Minxian-Zhangxian M_S6.6 Earthquake

      2013, 35(3):471-476.

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      Abstract:Earthquakes and rainfall are two main factors to induce landslides.Generally,these two events rarely occur at the same time.However,their coupling occurred in a widespread region during a loess earthquake landslide caused by the Minxian-Zhangxian MS6.6 earthquake on July22,2013,which resulted in significant losses of life and property.The characteristics of development and influencing factors of two typical earthquake landslides including the Yongguang and Puzi landslides are investigated on the basis of site survey,rainfall data,and aerial images.The results indicate that many earthquake landslides are distributed in a band in accordance with the trends of seismo-tectonics.In addition,moisture content was above the plastic limits of loess in the Yongguang landslide,which showed characteristics of mudflow.The reasons for its occurrence differ from previous earthquake landslides and include the coupled effects of excessive rainfall and strong ground motion.Moreover,strong ground motion was also the main factor in the Puzi earthquake landslide,in which the slide distance was very short and continued 40min following the earthquake.Such investigation results of the two typical loess earthquake landslides are very helpful for the prevention and control of earthquake landslides in the future.

    • Microtremor Measurement Research of Amplification Effect in the Loess Site of the MinXian-ZhangXian M_S6.6 Earthquake

      2013, 35(3):477-482.

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      Abstract:An MS6.6 earthquake occurred on July 22,2013,in Minxian-Zhangxian,Gansu province,and the amplification effect of the loess site appeared in meizoseismical area.To explain the principle of amplification effect of loess site in theory,we measured and researched two typical loess sites by using microtremor measurement.The results show that,the damage of adobe house is more serious on the summit than on the gully.On the summit the damage of adobe house is serious and there are even entire collapses,but on thethe gully there are cracks and not collapse of adobe house.The intensity difference between the summit and gully is intensity Ⅰ~Ⅱ,which shows obvious amplification effect of the massif.In the paper,we have made contrastive study of the predominant frequency of microtremor measurement by choosing two typical areas of the obvious amplification effect of loess site at the meizoseismal area(intensity 8),which are Yongxing village and Daleng village,Majiagou village and Xinglin village in Meichuan town,Minxian County.At Yongxing village and Majiagou village,the damage of adobe house is serious and there are entire collapses.However,at Daleng village and Xinglin village,there are cracks and not collapse of the same adobe house.The earth pulsation has rich geophysics information,which is aggregation of body wave and surface wave.In the paper,the principle,test method and causes of ground microtremors are introduced.According to engineering examples,the determination for the predominant period of a site is described,moreover,its application in evaluation for the category of the site and soil and the effect of different site conditions on the characteristics of frequency spectrum are analyzed.The results show that the thick soil and thin soil structure obviously affect the frequency spectra of the ground microtremors,and there are corresponding relationships between them.The research results show:the characteristic of predominant frequency of the site is obvious in the covered loess area,in which the predominant frequency is lower on the summit than on the gully,the range of which is 1~2Hz and 3~6Hz respectively;Meanwhile,with the increase of the altitude of the loess site,which shows the distribution characteristic of thick loess,the range of the site predominant frequency is 1.3~1.8Hz,which is similar to the predominant frequency 1 Hz of earthquake observation wave and shows obvious amplification effect of the site,which is the same with the actual damage fact.

    • Estimation of Peak Ground Acceleration in Magistoseismic Area of the Minxian-Zhangxian M_S6.6 Earthquake

      2013, 35(3):483-488.

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      Abstract:The horizontal peak ground acceleration(PGA)distribution in an earthquake is a very important parameter and can be used as a reference for the determination of seismic intensity.In Minxian-Zhangxian MS6.6 earthquake disaster region,there is only Minxian seismostation in intensityⅦregion got the seismic records and in intensity Ⅷ region there is no seismic record.During site investigation,a kind of brick doorpost was noticed in Lalu village in Hetuo town,meizoseismal area.The doorpost with iron door broke in the earthquake and the doorpost without iron door kept in good condition,which can be used to estimate the PGA in this area.Based on the field investigation,the destruction features in meizoseismal area of the Minxian-Zhangxian MS6.6Earthquake are sketched and the damage to the brick doorpost with iron door in earthquake are described and analysed.The seismic intensityⅧregion is about 706km2 and the most serious damage area include Yongguang,Yongxing and Lalu villages,most of them located in the high half slope covered by thick loess.According to the characteristics of the doorpost and its break,the earthquake horizontal PGA was estimated by mechanics analysis theory using a simplified strut-node model,which can be used as a reference for seismic intensity division and post-disaster reconstruction design.The results show that the earthquake horizontal PGA of Lalu village in Hetuo town,meizoseismal area,is up to 5.1~5.4m/s2,namely 0.52~0.55g,which is much greater than the reference value of eight-degree region in the Chinese Earthquake Intensity Scale.Judging by the related study about the influence of local topography on ground motion in mountain region of southern Gansu province and the seismic records observed on Shangcheng platform in Wenxian during Wenchuan MS8.0earthquake,the high PGA may be caused by the amplification effects of both high mountain slope and thick loess in study area.Compared with the PGA value of seismic record by seismostation in Minxian-Zhangxian MS6.6earthquake and Lushan MS7.0earthquake,the PGA value is usually much higher than the reference value in the Chinese Earthquake Intensity Scale of the same intensity region.Therefore,these two effects should be considered for the post-disaster reconstruction and seismic fortification in the future and the fortification criterion should be increased for villages in high half slope area.

    • Strong Mmotion Records and Its Characteristics in MinxianZhangxian M_S6.6 Earthquake on July 22,2013

      2013, 35(3):489-496.

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      Abstract:The Minxian-Zhangxian MS6.6 earthquake occurred on July 22,2013,at Minxian country,Gansu province(34.5°N,104.2°E),which had resulted in 95persons dead and 1366persons injured until July 24,2013.Digital strong ground motion records of high quality have been obtained in this earthquake for the third time in China following the Wenchuan earthquake and the Lushan earthquake.64strong motion stations installed in Gansu,Sichuan and Shanxi province were triggered and acceleration records in the main shock werewere obtained.In this paper,the preliminary characteristics of these records were analyzed including the spatial locations of these stations,the number of records within different epicenter distances and PGA contours.Comparing the observed data with the attenuation relationship(ground motion prediction equations:one is HUO(1989)and another one is Italy08),it has been found that the observed PGAs and spectral accelerations are remarkably lower than the empirically predicted ones.In general,the far-field strong ground motion is much lower;however,long-period ground motion attenuates slower than the near-field ground motion due to the particular traveling path and site effect.The reason of the amplification is that some stations located in the center of the basin have a thick overburden than the station located at the edge of the basin.The analysis of the far-field records obtained in Weihe Basin indicates the predominant period become longer.Housner G W proposed IHas an effective intensity measure to correlate seismic severity with structural damage to buildings.For this reason,records and code values have also been compared in terms of IH.By analyzing the Macro seismic intensity and Housner spectral intensity and consulting the geological characteristics of Minxian,the good correlation between the earthquake damage and seismic intensity has been preliminarily presented.Because of the economic backwardness,the houses in rural areas are mainly of masonry structures,of which the seismic performance is poor.Many houses are severely damaged in the earthquake,especially the houses near the epicenter in Minxian country.Most of them are sited in poor geological region,such as valleys,steep slopes andhills.What's more,the slope effect amplifies the effect,so the houses are damaged more seriously.The original structure of loess looses because of the ground motion,and then led to the landslides.So the Minxian-Zhangxian earthquake was not very strong,but the earthquake also caused a lot of geological disasters.The macro intensity of China has the characteristics of integrated indicators.This study has an important role on ground motion characteristics and engineering damage investigation in the western region of China.Strong motion records in Minxian-Zhangxian earthquake can be used in further study of ground motion characteristics by combining with that in the Wenchuan earthquake and Lushan earthquake.

    • The Strong Motion Records and Preliminary Analysis for Minxian-Zhangxian M6.6 Earthquake in Gansu Province

      2013, 35(3):497-502.

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      Abstract:The Minxian-Zhangxian MS6.6 earthquake occurred on July 22,2013,at the junction of Minxian and Zhangxian,Dingxi,Gansu Province(E 104.2°,N 34.5°).The depth of this widespread earthquake was shallow,which caused huge casualties and property losses.In this region,numerous professional strong motion observation stations recorded valuable acceleration records that accurately reflect the ground vibration of the main shock in the corresponding region of Gansu province and play an important role in the evaluation of earthquake development trends.In the present study,these acceleration records were collected and preliminary processed,and the results of peak ground acceleration were statistically analyzed.We determined that 47strong motion stations obtained acceleration records,which included four types of strong motion seismographs such as MR2002,Etna,GSR-18,and GSMA-2400.The Minxian strong motion station was the closest to the epicenter at a distance of 18.0km and peak accelerations of 160.7gal(EW),172.5gal(NS),and 78.4gal(vertical).The farthest station from the epicenter was Songshan at a distance of 297.3km and peak accelerations of 3.3gal(EW),3.1gal(NS),and 2.0gal(vertical).By calculation,we ascertained that the EW,NS,and vertical acceleration values were 1.2~160.7gal,0.4~172.5gal,and 0.4~78.4gal, respectively.This earthquake decayed quickly,and the peak acceleration of stations 100km from the epicenter was only approximately 10gal.For this earthquake,the Minxian station showed the largest peak acceleration. Located in the Minyang township of Minxian,this station is situated in a good observation environment with stable equipment;therefore,the records obtained by this station are reliable.In addition,the peak ground acceleration of each station gradually reduced with epicentral distance.However,But the effects of anisotropic media and site conditions may have resulted in unequal peak ground acceleration values for different locations at the same epicentral distance.Although the Lintan strong motion station was 79.5km from the epicenter,its peak acceleration was only approximately 5gal.The Songshan was farthest from epicenter;however,its peak acceleration was not minimal.These special conditions may be associated with local geological formations and site environment.On the basis of the peak acceleration obtained by each station,we used the Kriging interpolation method and plotted the peak acceleration map of the Minxian-Zhangxian earthquake.The simulated values accurately reflected the ground motion intensity of the earthquake for each observation point to provide basic information for research on the characteristics of strong ground motion and seismic engineering.Moreover,this map can provide an important basis for rapid damage assessment and earthquake emergency planning.In this study,the work was preliminary pending further research after accumulation of supplemental data.

    • Regional Crustal Movement Background and Cross-fault Deformation Anomaly Characteristics Prior to the Minxian-Zhangxian M_S6.6 Earthquake

      2013, 35(3):503-512.

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      Abstract:In this study,the regional crustal movement background is analyzed using various types of regional crustal deformation data including vertical deformation,GPS,mobile gravity,and cross-fault short line observation in the Minxian-Zhangxian MS6.6 earthquake zone located at the northeastern margin of the Qinghai-Tibet block.On the basis of regional geological structures,dynamic environment,and existing research findings,the anomaly characteristics of crossfault deformation and its possible mechanism also are discussed.The results show varying degrees of medium-and long-term seismogenic backgrounds in the west Qinling and Liupanshan tectonic province such as a GPS horizontal compresso-locked zone with high strain accumulation andan anomalous GPS vertical uplift belt with a high gradient,in addition to an abrupt change in the pull of gravity prior to the Minxian-Zhangxian earthquake.Moreover,a fault deformation anomaly near the Lintan-Minxian fault caused the earthquake,and its peripheral-related structure realm showed significant temporal and spatial fluctuation up to the time of the earthquake.Particularly since the Wenchuan MS8.0earthquake,the abnormal fluctuations of cross-fault deformation have reflect that the influences from the active dextral rupture of Longmen Mountain seismogenic structure adjacent to the regional tectonic belt have promoted the formation of this tectonic province and the seismogenic process of the Minxian-Zhangxian earthquake.Further,varying degrees of medium-and long-term seismogenic backgrounds exist in the area;therefore,it is difficult to determine the impending earthquake stage because few earthquakes above 6have occurred since the data of crustal deformation in this region has been accumulated.Nonetheless,earthquake data must be continually accumulated,evaluated,and improved.

    • Geo-electrical Forecasting and Observation prior to and following the Minxian-Zhangxian M_S6.6 Earthquake of 2013

      2013, 35(3):513-521.

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      Abstract:This paper presents geo-electrical research in earthquakes and their forecasting performed prior to and immediately following the Minxian-Zhangxian MS6.6 earthquake and appraises the observation data anomalies in apparent resistivity that appeared at stations in southeastern Gansu and its adjacent areas.The results of the research roughly agree with observation data of the actual principal earthquake and its strong aftershocks.In addition,the observation data anomalies include the anomalous information in apparent resistivity,which is directly associated with the earthquake and the data anomalies in apparent resistivity caused by certain disturbance factors.Therefore,the results have scientific significance in earthquake forecasting and obvious uncertainty;however,the testing is only tentative.Moreover,this paper examines several important factors in geo-electrical observation such as environmental protection because daily environmental disturbances have gradually restricted further development of such observation on the earth’s surface.After surveying the operational aspects of geo-electrical stations,it is determined that developments in down-hole observation configurations or remote unmanned stations may lessen environmental disturbances when environmental protection is not possible.

    • Retrospective Study on the Trend of Apparent Precursors of the Minxian-Zhangxian M_S6.6 Earthquake with the Triplet Method and "Activity in Quiescence" Method

      2013, 35(3):522-528.

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      Abstract:The triplet method is an analysis method based on the time frequency of the M > 7.0 earthquakes.A specific approach is used for studying the time series of great earthquakes occurring in the past in a certain region by using a time series composed of periodicity,multiple periodicity,and golden section.If they fit well,we can use it for predicting the time of a future earthquake by the time series."Activity in quiescence" is a method for analyzing the seismic activity on the basis of considering the earthquakes in a low-tide period as a precursory index for predicting the earthquakes in a high-tide period.It calls approximately one decade when no M >7.0earthquakes occurred in the Mainland China intermittent period,then subtracts two years from both ends of the intermittent period to eliminate the influence of the start and the end of the earthquake climax;hence,the rest of the period is called the quiet period.In the places where M6.0earthquakes occurred in the quiet period,the M ≥ 7.0earthquakes may occur when the climax of the next earthquakes is reached.By aiming at the Minxian-Zhangxian MS6.6earthquake that occurred on July 22,2013,in this paper,we reviewed and analyzed the apparent precursors and prediction process before the earthquake with the triplet method and"activity in quiescence"method.The results show that, after using the triplet method to analyze historical earthquakes of magnitude 8,magnitude 7 and magnitude 6that occurred in the southeastern Gansu,in 2012we predicted that an MS6earthquake would occur in Tianshui in the 2013-2014period,and the prediction location was withina 150km radius of Tianshui.In addition,because the magnitude and seismogenic year of the Diebu MS5.8earthquake occurring on January 8,1987were similar to the index of"earthquake of activity in quiescence",we used this earthquake as the index of a"quasi-activity in quiescence",made a time prediction with the triplet method,and then predicted that from 2012to 2014,an MS6~7earthquake would occur in a 150km radius of the location of the Diebu MS5.8earthquake.Because of the complexity of earthquake prediction,after analyzing the whole country and Gansu province by using the index of the triplet method and"activity in quiescence"method,we found that there were more significant precursor shows in other regions,so the prediction on the southeastern Gansu was just listed in the second program of earthquake risk.In 2012we only obtained an investigational prediction result,but not put forward a prediction advice.The reality is that the Minxian-Zhangxian MS6.6earthquake occurs in the location of a"quasi-activity in quiescence" earthquake;however,this earthquake shows that the triplet method and"activity in quiescence"method still display earthquake precursory indicators,and the"quasiactivity in quiescence"indicators are worthy of attention.Comparing to the commonly used prediction methods for medium-term prediction,the triplet method can point out a specific time period in the background of strong earthquake,which is its obvious feature.If combined with a variety of other methods,the triplet method will further enhance its efficiency of predicting strong earthquakes.

    • Coseismic Changes of Water Level Caused by the Mianxian-Zhangxian M_S6.6 Earthquake

      2013, 35(3):529-534.

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      Abstract:On the basis of research reported during the past few decades and data from the national underground fluid precursory network,this study examines the coseismic changes of water level caused by the Minxian-Zhangxian MS6.6 earthquake.Coseismic change was observed in only one water well level in the static strain field with an epicentral distance of≤1.5the fault rupture length,and its amplitude was only 1.5cm.Such static strain is not likely to trigger further earthquake activity.The total water level changes in observation wells indicated that the distance between the water level changes to the epicenter was distributed from 230km to 1470km.In the far field,in which the epicentral distance was larger than 1 000km,coseismic changes were observed in two observation well,both of which showed abrupt water level changes.The mechanism and characteristics of this result could indicate the dominant factor between the elastic-plastic spread and shutting of the rock fracture shown by the influence of quaking around the wells.When the elastic-plastic spread was less than the shutting,the decreased rock porosity resulted in ajump in observation well water level.Moreover,eight observation wells showed coseismic changes of water level in the entire Chinese mainland,which is less than the number of the earthquake coseismic changes.The distribution of the coseismic changes of water level in the wells was large and irregular with geologic structure.From the perspective of all the coseismic changes in observation wells,six observation wells showed abrupt changes in water level.Such increases were the main type of change and were attributed to 75%of the total coseismic changes in water level.Regional tectonic stress should have been released by the Minxian-Zhangxian MS6.6 earthquake.In addition,the structure and hydrogeological conditions of the observation wells were key to the coseismic changes in the water level,and the lithology effect of the observation wells on the coseismic changes was far less than the distance effect.

    • Contrastive Study on Co-seismic Response Characteristics of Well Water Temperature in Wenchuan(M8.0),Yushu(M7.1), Lushan(M7.0)and Minxian(M6.6)Earthquakes

      2013, 35(3):535-541.

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      Abstract:The study of co-seismic response is one of the most direct and effective methods of revealing the stress and strain response law of the crust,which a key issues in Earth science.To some extent,the co-seismic response of groundwater temperature reflects the crustal deformation and ground vibrations caused by subsurface deformation,pores,or fissure changes,and vertical migration of groundwater.The 2008 Wenchuan(MS 8.0),2010Yushu(MS 7.1),and 2013Lushan(MS 7.0),and Minxian(MS 6.6)earthquakes had substantial impacts on subsurface fluids in the Chinese mainland;however,the co-seismic response characteristics caused by the four earthquakes differed significantly.The range,magnitude,and duration caused by the last three earthquakes were far lower than those of the Wenchuan earthquake.Although the response characteristics caused by the Yushu and Lushan earthquakes differed,they had essentially the same magnitude.The co-seismic effect caused by the Wenchuan earthquake was significantly higher than that of the other earthquakes.Although seismic responses were noted throughout the entire Chinese mainland after the Wenchuan earthquake,similar shock responses were detected mainly near the epicenters of the earthquakes.The co-seismic effects caused by the same-magnitude Yushu and Lushan earthquakes also differed.For example,the effect was observed in North China,central China,Sichuan,Yunnan,and Tibet after the Yushu earthquake;however,that of the Lushan earthquake was concentrated mainly near the epicenter in Sichuan,Yunnan,Chongqing,and other areas.Therefore,the influence of Yushu earthquake may be much larger than the Lushan earthquakes.The co-seismic amplitude of the Wenchuan earthquake was generally higher than that of the other three earthquakes;however,it was significantly higher near the epicenter of the earthquake.The depth of sensors in the well water had a very strong influence on co-seismic response because the co-seismic direction and magnitude differed when the water temperature sensor was placed at different depths in the same well.This phenomenon may be related to epicentral distance and magnitude and may be affected by the rupture mechanism and the stress and strain sensitive extent response to aquifer media of the observation points.

    • Study on Abnormal Features in EW Displacement before Minxian-Zhangxian M_S6.0 earthquake in Gansu

      2013, 35(3):542-548.

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      Abstract:The China Earthquake Network Center recorded an MS 6.6 earthquake at 7:45CST on July 22,2013,at the boundary of Minxian and Zhangxian in Gansu province.The earthquake was located in the western region of the Qinling Mountains in southern Gansu along the north branch of the Lintan-Dangchang fault.Thirteen counties were affected in the VI degree zone and above. Immediately following this earthquake,the data from 10Global Navigation Satellite Systems(GNSS)stations of the Crustal Movement Observation Network of China recorded from July 2,2012,through July 4,2013,were analyzed to determine that nine earthquakes of magnitude≥MS6.0occurred during this period in China’s mainland and adjacent areas.Analysis revealed that the horizontal component of the displacement time series curves differed prior to and following these earthquakes.Two of the most recent earthquakes showed obvious,significant changes indicating that north-south component is a weaker earthquake indicator than the east-west component.Since June 1,nearly all reference stations recorded obvious changes.The variable quantities were more than 10mm and significantly exceeded this value in two days.This large variation was particularly notable after June 23,approximately one month prior to the earthquake.Several reference stations showed significant changes in eastern displacement.The Jingning and Lanzhou stations showed changes at the same time on June 23to June 24with amplitudes of 18.1mm and 20.9mm,respectively.The Dingxi station showed a significant change on June 27 with amplitude of 22.7mm.In comparison,changes at Dingxi,Maqu,and Qingshui stations were not significant changes between June 29and July 5.However,stations distributed north-south frequently showed changes greater than 10mm changes,and those located farther from the earthquake’s focus generally occurred earlier.The displacement time series did not show consistency between in east-west and north-south distribution.Not reference station registered abnormal changes in horizontal displacement before the earthquake,and the changes generally were not synchronized.Some deformation occurred on or following the earthquake that differed among stations.However,all of these precursor characteristics are considered meaningful.The displacement component alone is insufficient for determining precursor anomalies;rather,a combination of various observation methods and a variety of earthquake monitoring data are necessary for identifying anomalies,which should include integrated information various different angles.Although changes were detected in the results,such anomalies weakly suggest the seismogenic moment of an upcoming earthquake and do not clearly to confirm earthquake location.To address this challenge,further research and in-depth analysis are required for earthquake prediction.

    • Analysis of the Relationship between Abnormal Ground Deformation of Gansu and the Minxian-Zhangxian M_S6.6 Earthquake

      2013, 35(3):549-556.

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      Abstract:Minxian,located in southwestern Dingxi City of southern Gansu in the eastern region of the Qinghai Tibet Plateau,borders on Longnan and the West Qinling Mountains and is the geometric center of Dingxi,Tianshui,Longnan,and Gannan.The geological structure of Minxian belongs to the Qinling Mountains Hercynian geosyncline fold belt at the north branch of the Western Qinling Mountains fold belt.At 7:45CST on July 22,2013,an MS6.6 earthquake occurred at the junction of Minxian and Zhangxian with a focal depth of 20km.The earthquake occurred along the north branch Lintan-Dangchang fracture,126km from Dingxi and 17km from Minxian County.Strong tremors were felt by residents in Dingxi,Tianshui,Longnan,and Gannan;those in Lanzhou and Baiyin also detected movement.The Earthquake Administration of Gansu province operates 8deformation observation stations and 15deformation observation projects situated within 300km of the earthquake focus that include DSQ and SSY at Tanchang station;CZB at Wushan station;CZB and YRY at Linxia station;YZ-1at Liujiaxia station;CZB at Lanzhou station;DSQ,SSY,SSY-II,SSQ,and PET at Lanzhou Shilidian station;and DSQ and SSY at Baiyin station.This study focuses on the data of 15observation projects to conduct preliminary analysis,through which abnormal variation was detected in the data of 10projects.Moreover,DSQ and SSY at Tanchang station and CZB at Lanzhou station showed obvious β,β2,and γ1 stages,and CZB at Wushan and Liangshui exhibited obvious β1 and β2 stages.Therefore,deformation anomalies were present prior to the MS6.6earthquake.Although the distance between Lanzhou and Shilidian stations is less than 10km,only DSQ,SSY,and SSY-II at Shilidian exhibited a significant bulge anomaly;SSQ of Shilidian showed no obvious abnormalities.Sucha huge discrepancy in such a close proximity required further explanation.It was determined that the CZB component at Linxia station began to increase rapidly in January 2011and entered a declining trend in August.At the same time,the EW component began to alter from a normal decline,which resulted in significant deformation.These changes are unrelated to the NS component.Therefore,further research is needed to determine the reason for such anomalies.

    • Study on Wave Velocity Ratio(vP/vS)Variation Characteristics of Minxian-Zhangxian M_S6.6 Earthquake Sequence,Gansu Province

      2013, 35(3):557-561.

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      Abstract:Collecting fixed stations and six ambulatory stations observational report of MinxianZhangxian MS 6.6 earthquake sequence,extracting travel-time information of P-wave and S-wave, using the multi-station method to compute wave velocity ratio of this earthquake sequence.The results show that there is a decreasing trend of velocity ratio before strong after-shocks.It is of reference value and indicative significance on the short-imminent term prediction of strong aftershocks. Although the wave velocity ratio anomaly is still a controversial issue,domestic and foreign scholars have made some achievements in theory and practice.In 1928,the Japanese seismologists Wadati Kiyoo first proposed the calculation method of wave velocity ratio:multi-station method.In 1962,the Soviet Union scholar Semionov published the first results of velocity abnormal in Garm region,found wave velocity anomaly and wave velocity ratio anomaly before earthquake magnitude greater than 3.5.In the early 1970s,Japan,the United States and other countries have also found a lot of wave velocity anomaly before earthquake.Especially American scholar Aggarwal found the change of wave velocity ratio anomaly before several small earthquake(the maximum magnitude is 3.3)in earthquake group and proposed to explain the anomalous with DD mode.At the same time,domestic scholars got some useful results in this field.In 1970s,Feng et al.summed up in the evolution of the crust,physical properties of medium will produce a series of changes,such as the emergence of micro fracture,expansion,seismic waves through the earth’s crust medium,and velocity will change accordingly,which is an important basis for the study of the wave velocity ratio of the medium.Wang et al.(2011)made a further research of variation characteristics of wave velocity ratio before and after the Wenchuan earthquake.Feng et al.(2009)studied the average wave velocity ratio in the northeastern margin of Qinghai-Tibetan Plateau,and found that there is a certain difference in the spatial distribution of wave velocity ratio.Li et al.(2006)found strong aftershock wave velocity ratio before trend decline.Based on the previous theoretical and the actual data,we conclude that the average wave velocity ratio of this sequence is 1.713,which is consistent with the results of Feng et al.(2009).It is a different levels of wave velocity ratio decline trend before the aftershocks with ML≥3.0occurred.Most of the aftershocks with ML≥3.0occurred in the process of the wave velocity ratio of sequence pick-up after down to the lowest,however,only a few aftershocks with ML≥3.0occurred while wave velocity ratio in the process of down to the lowest.

    • It Brooks No Delay to Research and Solve Economically Feasible “Anti-seismic Farmhouse”in the Poor Mountain Areas

      2013, 35(3):562-562.

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      Abstract:

    • The Seismic Behavior Analysis of Near—field Multi Pulse Ground Motion on Composite Isolated Structure

      2013, 35(3):563-568.

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      Abstract:In recent years,the base isolation technique has been widely accepted and promoted as one of the most effective approaches for earthquake resistance due to its security and reliability for use with near—field earthquakes.Some researchers have studied and discussed the influence of various Darameters including peak ground acceleration/peak ground velocity(PGV/PGA), input energy。peak values,and duration of the near—field earthquakes on the earthquake—resistant performance of constructions.Multi—pulse near—field earthquakes have a larger influence on the base isolation structure than do single—pulse near—field earthquakes;thus,more attention has been paid to the security problems of constructions under this working condition.The focus of this paper,therefore.is an isolation project in the northwest district in which the elastic—plastic response time history of near—field earthquakes was analyzed,and a viscous damper was added to improve the current earthquake—resistant performance of the base isolation structure.In this paper,a multi—pulse seismic wave in a near—field earthquake was simulated and synthesized using a MATLAB procedure and a combination of velocity impulse and broadband cornDonents.The design scheme for the X—type symmetrical distributed viscous damper was selected to reduce the additional internal force effect of the energy—dissipating brace on the beam and column construction of the structure.On this basis,a computational model and equation of motion for the composite isolated structure was established.The earthquake response of the base and composite isolated structures was measured under three working conditions including the El Centro wave,the near—field wave of the Chi—chi earthquake recorded at Tcu075 observation station,and an artificially fitted multi—pulse wave.Theoretical analysis and numerical simulation revealed the peak valueacceleration of the base isolation structure was larger than that of the composite isolated structure.The input energy of the structure increased progressively.In particular,the input energy of the seismic wave in the multi-‘pulse near—-field earthquake was greater than that of the Chi——chi wave and significantly greater than that of the E1 Centro wave.When an earthquake occurred。components with many structures entered the plastic stage owing to the input energy factor,which resulted in substantial weakness.However-the time—history curve for energy consumption of the damper revealed that the damper fully exerted its energy consumption under each working condition.The composite isolated structure was able to fully consider the energy consumption of the structure under the action of the near,?field earthquake and multi—pulse near—field earthquake to guarantee the security of the structure.Designers and engineering technicians have focused on displacement of the isolation layer and the bottom column axial force.After discussion and analysis,it has been determined that the complex isolation design is more feasible under the action of the near—field earthquake.This study examined the earthquake responses of structures under different working conditions including the function of multi—pulse near—field seismic oscillation on base isolation structures and the damping effect of composite isolated structures after addition of the damper.The results are summarized in the followicg points:1.The energy consumption of the complex isolation of a composite isolated structure has distinct advantages that can effectively reduce the number of components in the plastic structural system and improve the earthquake resistance ability of the structure in the near—field multi—pulse earthquake process;2.Under the action of a near—field earthquake,the displacement of the base isolation structure in the isolation layer becomes excessively large;and 3.The composite isolated structure can effectively reduce the axial force of the bottom column.

    • Transverse Seismic Performance of Beam Aqueduct Considering Water Mass Influence

      2013, 35(3):569-574.

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      Abstract:To analyze the transverse seismic performance of a large—scale beam aqueduct by considering the water mass influence,the aqueduct of the South to North Water Diversion Project is studied.Through a study of the fluid—structure coupling dynamical action method,we use an equivalent of a spring—mass system(simplified using the Housner water model)for simulating the dynamic interaction of the fluid and the aqueduct structure.The ANSYS finite element software is adopted to estimate the performance of a large-scale aqueduct with a beam.With the time history analysis method,we have investigated the transverse seismic response of the large-scale beam aqueduct using a few types of earthquake waves.Then,the natural vibration characteristics and the seismic response of the large-scale beam aqueduct are obtained considering the fluid-structure coupling interaction.The calculation results show that the water shaking function has a considerable influence on the dynamic characteristics of the aqueduct.The transverse seismic response of the beam aqueduct is significantly influenced by the water mass in the aqueduct.The water shaking function can effectively decrease the seismic response of the water itself.The transverse seismic response of the aqueduct is underestimated if the water in the aqueduct is ignored;however,if all the water in the aqueduct is regarded as a rigid body and appended to the aqueduct,the seismic inertia action of the water is seriously exaggerated and is unreasonable.Consequently,in the dynamic analysis of the large-scale aqueduct-we must consider the fluid-structure coupling interaction.We compare a case in which the fluid-structure coupling interaction is considered and that in which the fluid-structure coupling interaction is not considered;the former's maximum top displacement and bottom moment and the shear of piers are far less than those of the latter.Therefore,we conclude that the water mass influence on the seismic response of the aqueduct is limited.We compare the seismic responses of two different conditions of full trough(considering the fluid—structure interaction)and empty trough and find that the former7S maximum top displacement and bottom moment and the shear of piers are all greater than those of the latter.This is because the thankful water increases the quality of the upper portion of the aqueduct structure,which increases the seismic forces acting on the aqueduct.In the aseismic analysis of a large aqueduct,the influence of the water mass should be taken into account.When the water mass remains unchanged,and the aqueduct body changes according to the depth—width ratio,the natural frequency of the water in the aqueduct and the natural frequency of the aqueduct vibration change;however,the changes are not considerable.The change of the largest displacement of the piers on the top and the greatest moment and shear of the piers at the bottom depended on the depth—width ratio.Therefore,while selecting an aqueduct section,we should take the depth—width ratio of the seismic response of the piers into account.To some extent,the selection of a reasonable section can reduce the seismic response of the aqueduct.The fluid—structure interaction of the fluid and the aqueduct should be known for the estimation of both the impulse pressure and the convection pressure.The sloshing fluid produces a complex reaction on the aqueduct body;hence。we cannot simply consider all water quality values to be the added mass to the aqueduct body.

    • Design Research on the Irregular Double Grid of the Yadan Sightseeing Tower

      2013, 35(3):575-581.

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      Abstract:As architecture breaks away from traditional styles,grid structures with irregular spacing are in demand to meet construction requirements.An example of current architectural style is the Yadan sightseeing tower,which has an irregular double—layer steel grid roof.In this work,the engineering of such structures was reviewed and analyzed,and analysis and calculation of layered steel roof structures under seismic and wind 10ads were performed.The calculations assumed that part of the bar was damaged,and a damage assessment of the residual bearing capacity was conducted.Next,a finite element model that illustrated the 10ads imposed on the structure was built with analysis software.Then,a nonlinear time history analysis of earthquakes and a natural vibration analysis were done with the ANSYS finite element analysis software.Displacement curves showing the time history of key nodes and the stresses on key bars were obtained.Wind 10ad analysis using computer-aided design software of the space grid structure(MST2010)was done,and displacement and stress distributions were obtained.Last,the analysis results indicated that some of the key bars assessed preliminarily might be damaged,so a damage assessment of the residual bearing capacity of the structure was undertaken.The results showed that the irregularly spaced grid structure in this project can be adapted to the current trends in architectural style.The grid not only reflects current architectural style but also has excellent seismic and wind resistance performances,similar to those of the traditional spatial structure.Therefore,irregularly spaced grid structures are appropriate for use in similar projects with steel roofs.To assess earthquake response,the structure was subjected to structural vibration modes,and the weak parts were the head,tail,wings,and joints.Horizontal stiffness was greater than vertical stiffness.The structure was in a fully elastic state under the effects of multiple earthquakes;however,only a portion of the bar yielded under this rare earthquake scenario,and plastic deformation appeared in accordance with the basic principles of structural design.Parts of the bearing bars section should be increased at design time because it is a key member of the entire structure.Because a streamline design was adopted to resist wind,the design of this structure satisfies the requirements for wind resistance even in a hostile environment.In this study,the key bar calculations were very important to the bearing capacity of the structure.During structure construction and in service,great importance should be given to these bars.Once damage appears,the bars should be reinforced in a timely manner.The caseload design and analysis results can be combined for some practical projects,assuming some structural failure and through a method to evaluate structural residual strength to identify the key bars in the structure.Such projects would provide guidance for the structure's construction and later use.

    • GPU/CPU Cooperative Coarse-grained Parallel Computing and Its Application to Regional Seismic Damage Predicction

      2013, 35(3):582-589.

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      Abstract:Refined model and dynamic time-history analysis have been deemed as a promising way to improve the accuracy of seismic damage prediction in urban city.However the high cost of traditional CPU computing platform hinders the extensive use of this method.In order to solve this problem,the GPU/CPU cooperative coarse-grained parallel computing approach,featured in high efficiency and low cost,is adopted to realize the regional seismic damage prediction with dynamic time-history analysis and refined structural model.This paper introduces the program architecture,calculation model and the parameters selection of the proposed method.The efficiency is discussed in detail and the method is implemented to a mid-size city,by which the advantages of this method are demonstrated.

    • Model Test on Dynamic Response of Layered Slopes with Different Thicknesses

      2013, 35(3):590-596.

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      Abstract:Using shaking table tests,we studied four layered slopes with different overburdened soils by increasing the horizontal sine acceleration time history as the input to analyze the impact of the thickness of the overburdened soils on the stability of the layered slopes.The failure position,property,pattern,and disadvantageous thickness of the overburdened soil were thoroughly investigated,and the relationship between the slope magnifying effect and the altitude was verified.A mode analysis was conducted for the test model using MIDAS/GTS to study the relationship between the self-vibration frequency and the thickness of the overburdened soil.The test results indicated the following:(1)The first failure plane was observed in the middle and the upper parts of the slope where the maximum response was found to be in the model slope in the case ofthe 6-cm-thick overburdened soil.(2)The failure patterns were different for the slopes with different thicknesses of the overburdened soil.In the case of the slope of a relatively thick overburdened soil,the fissures occurred first on the higher part of the slope and kept spreading until the entire slope collapsed in the avalanche mode.(3)With an increase in the altitude,the peak acceleration tended to increase as well,but the maximum value was observed in the middle and the upper parts instead of at the crest of the slope,which implied that the altitude magnifying effect occurred not only in the homogenous slope but also in the layered slope.

    • Research on the Sensitivity of the Landform Factor of Landslide Development in Middle and High Mountain Areas

      2013, 35(3):597-603.

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      Abstract:In order to analyze the sensitivity of the landform factor of landslide development degree in altitude of more than 1300m middle and high mountain areas,the use of sensitivity analysis methods based on factor contribution rate,research in the alpine region,northeastern Guizhou slope form,slope,relative height difference of the three types of impact factor onlandslide development impact.All influencing factor on the frequency landslide development on the basis of the area and volume component contribution ratio,using the sequence assignment method to quantify the contribution rate of each component's contribution index,and the contribution of each component of the geometric mean of the index build sensitivity coefficients,quantitative analysis the three types of topography influence the sensitivity factors on the development of landslides in mountain areas.In order to analyze the effect of topography of middle and high mountain degree of sensitivity factor of landslide development,we selected slope shape,the terrain slope,relative elevation difference three influence factors in the northeast of guizhou 51landslides landform ofmiddle and high mountain areas,using sensitivity analysis method on the basis of data analysis,based on comprehensive factors contribution rate research of various kinds of landform factors on the sensitivity of landslide development of middle and high mountain areas.The research results show that step and convex slope form geomorphic evolution accumulation zone of the slope in the rear can provide larger gravitational potential energy,which belong to the sensitivity of the slope landslide development form factor.It can provide large gravitational potential energy.Terrain slope between 18°~22°slope and relative height difference between 40~80mshort slope are often distributed in the surface water of strong erosion area,it is easy to induce the shallow small landslides in a gravitational potential energy and under the joint action of strong groundwater.The gravitational potential energy and the joint action of strong groundwater is the main cause of the shallow small landslides.Topographic slope is greater than 27°extremely steep slope and relatively high elevation difference is greater than 120mdeep often cause large-scale landslide due to large have gravitational potential energy.Relative to the small scale landslide,it will cause a greater loss.At home and abroad at present,the impact factors of landslide development research in sensitivity,main is to reflect the disaster development density of frequency analysis and to reflect the development scale of area analysis,size analysis.The method is a method of quantitative sequence assignment method is used to quantify the contribution of each component contribution rate index,and the contribution index of the components in the geometric average build sensitivity coefficient,quantitative analysis of the three kinds of landform influence factors on the sensitivity of landslide development of middle and high mountain areas.In order to study the northeast slope of middle and high mountain qian form,terrain slope,relative elevation difference degree of the influence of three kinds of influence factors of landslide development,the article uses the sensitivity analysis method based on the comprehensive factors contribution rate,provide the basis for future similar research.

    • Design and Realization of a Seismic Monitoring Sensor Module

      2013, 35(3):604-609.

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      Abstract:Throughout the world,most of the existing seismic alarm systems calculate magnitude and locate an earthquake through the seismic network;the accuracy of early warnings is improved by increased network density.The accuracy of basic parameters of the earthquake will be correspondingly improved.However,it takes a lot of manpower,material,and other social and public resources to use this method.Meanwhile,the seismic network itself has shortcomings in the complexity of multi-stations and the vulnerability of the network system.Due to economic backwardness and communication underdevelopment,most parts of our country still lack an earthquake early warning system;these areas are in the earthquake belt,so it is necessary to provide a seismic alarm in this area.This paper is based on the principles of earthquake early warning,computer technology,and sensor technology.It introducess the principle of earthquake early warning and discusses the possibility of rapid determination of earthquake parameters using only a single seismic monitoring sensor module.We also complete the hardware and software design of the earthquake warning sensor module for seismic monitoring and expound the process to determine earthquake parameters algorithm in detail.After an earthquake occurred,the P-wave of seismic propagated to the seismic monitoring station.First,the sensor module system was triggered using the short-term average/long-fterm average(STA/LTA)technique and the P-wave was picked up automatically.Second,on the basis of a traditional method,we used the initial motion direction of the three P-wave components to determine the epicenter azimuth at the seismic monitoring station.Finally,we used the first motion displacement of the three P-wave components to determine the epicenter azimuth.However,due to the high error of the azimuth based on this method,we have improved it to calculate several seismic azimuths by using information from the P-wave initial motion,and the arithmetic mean is used as the final value of the azimuth.As earthquake magnitude has some mathematic statistical relation to the predominant period of the Pwave,and the maximum displacement amplitude of different earthquake magnitudes has a certain attenuation relation to the increase of the hypocentral distance,we calculated the predominant period and maximum displacement amplitude with the collected acceleration data during the first three seconds after the P-wave’s arrival.Once the magnitude of the earthquake and the hypocentral distance are determined,a warning is sounded,achieving the goal of earthquake monitoring and early warning.The minimum acceleration the earthquake monitoring sensor module used here can distinguish is less than 1gal,and the range of acceleration is±2g.It also can collect acceleration of the three components simultaneously,and every sampling frequency could reach to 500 Hz.The power is 350mW under normal conditions;it is thus suitable for outdoor use.The maximum error range of the azimuth is±15°,and the average error is 11°;compared to the 8.5°average error of better seismic monitoring stations,the data here are a little larger,2.5°,because the earthquake magnitude and hypocentral distance are calculated by two statistical relationships,and it has a±0.412magnitude error and a±1.59kilometers hypocentral distance error.Compared to the traditional way that seismic networks determine earthquake parameters,the basic parameter calculated here has a larger error,but it has a lower demand for a single earthquake monitor to determine basic parameter of the earthquake.So it is practicable to determine the basic parameter of an earthquake by a single earthquake monitor sensor module.

    • The Kinematic Characteristics of Pdif-waves at CDSN Stations

      2013, 35(3):610-617.

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      Abstract:The traveling-time curve of the P-wave ends at an epicentral distance(Δ)of about 100°. At epicentral distances larger than 100°(Δ>100°),P-waves pass through the core-mantle boundary(CMB)and start to be diffracted around the core with speeds of~13.7km/s.The diffracted wave is termed Pdif. Due to the sharp decrease of the P-wave velocity at the core-mantle boundary from 13.7km/ s to~8.0km/s,the short period P-wave is strongly refracted into the core with speeds of~8.0 to 11.2km/s.This refracted wave is termed PKP(PKPab,PKPbc and PKPdf). The Pdif wave was first recognized on seismogram by Denmark seismologist Lehmann in 1936.The traveling-time curve of the Pdif wave was well defined at distances of 105°to 130°by seismologists Jeffres and Bullen in 1940,using the seismic data from 1930to 1940,for earthquakes with depths from 33to 794km.In 1991,the traveling-time curve of the Pdif wave was updated by Kennett[6]for distances of 100°to 144°and depths of 0,100,300,and 600km using seismic data from 1964to 1987. In the China Digital Seismograph Network(CDSN),the Pdif wave of strong earthquakes,whose distances range from about 100.2°to 179.0°,may be observed so that the Pdif phase can be analyzed perfectly.We collected and analyzed 124broad-band seismic recordings at the 11CDSN stations during aperiod of 1990to 2012,from very-far-field events with magnitudes of~6.0 to 8.8 and depths~4 to 631.3km.The kinematic characteristics of the Pdif phase are summarized as the following: (1)There is a good linear relationship between traveling-times and distances,and a systematic bias exists between our results and those of the IASPEI 1991table;for example,the difference reaches 11.2satΔ=100°,and 17.0satΔ=144°. (2)ForΔ>100°,the Pdif arrival time is about 4min and 10.7sto 29.8searlier than the PKP wave,and the time difference between the Pdif and PKP waves with distance could be formulated as:TPKP-Pdif=-2.835Δ+550.7 (h ≤100km) (100.0°to 179.0°). (3)The Pdif wave is about 4min and 5.4sto 6min and 42.0searlier than the PP wave,and the time difference between the Pdif and PP waves with distance could be formulated as:TPP-Pdif=0.014Δ2+5.562Δ-163.7 (h ≤100km) (100.0°to 179.0°). (4)For deep-focus earthquakes,the diffracted depth phases,pPdif and sPdif,may be observed.The time difference between pPdif-Pdif and sPdif-Pdif is similar to pP-P and sP-P. A time table,called the Traveling-time Table of the Pdif Wave at CDSN Stations,is proposed.The relationship between traveling-time and epicenter distance for Pdif is suggested to be:TPdif=4.573Δ+367.4 (h ≤100km ) (100.0°to 179.0°). The time table proposed in this study is a useful complement to the IASPEI1991table,and it could be used as a standard of Pdif wave analysis.It will be very useful for enhancing the earthquake analysis ability and accumulating analysis experience and for understanding physical characteristics of the mantle-core boundary.

    • Field Test on the Geochemical Detection of Concealed Fault in Hezuo City

      2013, 35(3):618-624.

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      Abstract:In recent years,soil gas has rapidly developed for wide application urban active fault detection because of its fast,convenient,high-efficiency,and low-cost characteristics.The measurement methods of Hg and Rn soil gases are established and are helpful for studying active fault detection and the hazard assessment.The focus of this research is determination of the position of the concealed fault and its occurrence to ultimately provide a target for further drilling and costeaning through analysis of the anomaly concentration characteristics of Rn and Hg gases in the soil.Due to the particularity of urban environmental conditions and the complexity of geological conditions to obtain more accurate and reliable results and thus better scientific analysis conclusions,it is necessary to conduct experimental research on the fault soil gas anomaly characteristics and influencing factors in the typical fields that have fault outcrops or drilling data prior to large-scale field detection and feature analysis.The goal of this project is to promote better control of geochemical exploration in Hezuo.The Hg and Rn soil gas concentrations were tested in two typical fault outcrops of Ganjia and Huangxiang gullies near Hezuo city,which is located in the western region of the northern rim of West Qinling. The results show that obvious anomalous concentrations of Hg and Rn gases exist in the fault zone,the peak of the concentration curve corresponds well to the fault location,and its curve can better reflect the nature and geometry of the fault.The results of six Rn and Hg measuring lines on two experimental sites indicate that the anomaly peak values are generally 1.5times higher than the background values and are grouped.In particular,the anomaly points are usually greater than twice the 1.5background value on the fault zone,and the curve exhibits the typical bow shape;the single abnormal point is considered to be the interference factor during observation.The Huang-Xiang gully on the west Qinling fault test site is the most typical,regardless of the instructions of abnormal points for the fault location or the response of the curve to the fault properties and geometric shape.In addition,Hezuo City is located in grassland.The surface is uniform,stable,low interferential and has beneficial vegetation cover.Therefore,it is desirable to detect the concealed fault by geochemical methods of soil gas and to trace the spatial and temporal variation characteristics of known active faults.

    • Experim ental Analysis of W eathering Tufflava on the Strength Properties in the South Fuj ian Province

      2013, 35(3):625-630640.

      Abstract (1219) HTML (0) PDF 399.09 K (1230) Comment (0) Favorites

      Abstract:As an important component of the Mesozoic volcanic rock in China,tufflava is widely distributed in the provinces of Guangxi,Fujian,Zhejiang,and Guangdong,and in Mesozoic volcanic basins of the M iddle to Lower Yangtze River area.Because of its special material composition and structure construction,tufflava is easy to weather under all kinds of exterior geological agents,such as water and atmospheric conditions.Usually many construction projects,especially tunnel excavations,will inevitably pass through this kind of rock mass.Therefore,it is very important to study the property of weathering tufflava for the design,construction,and stability analysis of tunnel engineering,as well as other engineering projects.This paper researches weathering tufflava,which belongs to the tunnel surrounding the rock of the Fujian Quanshan Highway in the south Fujian province.Uniaxial compressive strength and water absorption experiments are conducted on tufflava with different weathering degrees(strong weathering,weak weathering,slight weathering,and unweathering tufflava)with the intent to quantitatively analyze the effect of the degree of tufflava weathering on the uniaxial compressive strength and water absorption characteristics.The process for the experiments can be described as follows.Based on the standard test method for engineering rock masses,38 pieces of standard samples(50 mm ×50 mm× 100 mm)were prepared,with the drying and saturation processes strictly performed by the standard.There are two ways,boiled saturation and natural saturation, to saturate tufflava with different weathering degrees in water absorption experiments.In addition,strength tests of tufflava with different weathering degrees under air— drying and saturated conditions were conducted by the model YAW-2000 pressure tester.During the strength tests,we chose 1oad control mode and set the maximum axia1 compression to 1 000 kN and the loading speed to 0.75 MPa/s.The relationship between water absorption and the weathering degree under the conditions of boiled saturation and natura1 saturation were obtained.In addition。the relationship between strength and weathering degree under the conditions of air—drying and saturation were also obtained.It was found that the degree of weathering has a significant effect on the water absorption property and uniaxial compressive strength. The stronger the weathering degree is,the higher the water absorption shows,and the smaller the uniaxial compressive strength is.Finally,we fit the analysis of the uniaxial compressive strength and water absorption based on the data which has also been studied by using logistic regression models.The results show that the uniaxial compressive strength of tufflava with different weathering degrees under air-drying and saturation conditions has a nonlinear relationship with water absorption.The maximum error is 14,which can completely meet the project accuracy requirements.This non—linear relationship formula can be applied to strength estimations of rocks similar to the weathering tufflava in this paper.

    • Genetic-analysis of the Yellow River Big Bend in the Shapotou Area,Ningxia Hui Autonomous Region

      2013, 35(3):631-640.

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      Abstract:The Shapotou area is located in Zhongwei city in the Ningxia Hui Autonomous Region,which is also situated in the arc area on the northeastern side of the Qinghai-Tibet plateau with very active neo-tectonic movements in mainland China.The Yellow River crosses the Xiangshan-Tianjingshan fault and flows through the Shapotou.The Xiangshan-Tianjingshan fault is mainly a left-lateral strike-slip.The Yellow River formed a beautiful geomorphological meander,the Big Bend,which is similar to the "Ω" type.It developed three river terraces on the convex bank since it turns around in the Shapotou area.Over the past few decades,geologists have conducted many studies in this strong neo-tectonic movement and special tectonic setting,concerned with active faults,the tectonic deformation process in the Quaternary,the scales and rates of active fault displacement,and the causes of the Shapotou Big Bend.However,there is not a comprehensive analysis of the origins of the Big Bend.The research on the river terrace is one of the most important topics in geomorphology.River terraces are the most reliable records of river histories.The meandering river is ubiquitous in nature;meandering is a natural property of rivers. This paper focuses on the characteristics and ages of river terraces and analyzes the causes of the Big Bend to explore the causes of landforms in this area from the vertical and horizontal directions.Based on field investigations and comparisons to former studies,three terraces were revealed.The formation age of the highest terraces is~170ka B.P.The T2 and T1terraces were subsequently formed at~70ka B.P.and 8ka B.P.,respectively.The three river terraces in the Shapotou Big Bend formed mainly due to tectonic uplift,while the impact of climate change is not obvious on the formation of the terraces.Climate change is not the only element that controls river incisions:the terraces in this area depend on tectonic uplift.In the context of strongly regional neo-tectonic activities,when the Zhongwei Basin was elevated in approximately the Late Pleistocene,resulting in the fixing and down-cutting of the Yellow River,the highest terrace(T3)began to form.The T2and T1terraces were subsequently formed.This indicates that there have been at least three intensive tectonic movements.These three events are at least comparable to the" Gonghe Movement" and" Ruoergai Movement."According to the largest of the left-lateral displacements of the Xiangshan-Tianjingshan fault,which is less than 880m,the fault is not the only reason that the Big Bend formed.There are at least 2 200mdisplacements due to the river endogenous characteristics.Under the common function of the Xiangshan-Tianjingshan fault,which is a left-lateral strike-slip fault,and the rotation of the Earth's tilt toward power which is the natural evolution of water system,the Yellow River of the Big Bend in the Shapotou area is formed.The concave bank has been eroded and the convex bank has been deposited,so the planar shape of the Shapotou Big Bend is formed.River endogenous characteristics play more important roles than the strike-slip fracture displacements in the Big Bend.

    • Scale of Critical Seismogenic Region and Earthquake Prediction

      2013, 35(3):641-646663.

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      Abstract:The size selection of the critical seismogenic region prior to an earthquake has great influence on seismic hazard evaluation.By adopting an appropriate critical region,we can reduce the occurrence of false alarms and enhance the critical sensitivity of the precursory anomalies.In this study,we examine the optimal critical region scale using the load/unload response ratio(LURR)and accelerating moment release(AMR)methods.These two methods are intuitively reasonable.Prior to the occurrence of large or great earthquakes,the AMR phenomenon is usually observed.A simple power-law time-to-failure equation derived from damage mechanics can be used to model the observed seismicity.This hypothesis is an outgrowth of efforts to characterize large earthquakes as a critical phenomenon.The LURR is a short-to-intermediate-term earthquake prediction method based on measuring the ratio between Benioff strains released during the time periods of loading and unloading,corresponding to the Coulomb Failure Stress change induced by Earth tides on optimally oriented faults.Prior to the occurrence of large earthquakes(M>6.0),anomalous increases in the time series of LURR within a time frame of months to years has often been observed. A circular region is usually adopted as the spatial window in the LURR and AMR practices,allowing us to link these two unrelated subjects to investigate the optimal critical region prior to a large earthquake.In this study,the optimal critical region scale for LURR evaluation is determined by computing the anomaly within various-sized regions centered at the epicenter of the incoming large event to reach the maximum LURR precursory anomalies.For the AMR method,the calculation of the optimal critical region includes the following steps:The Benioff strain of earthquakes within each circular region is fitted to a power-law time-to-failure function and to a straight line;we then compute a curvature parameter as the ratio of the residuals to the powerlaw fit to the residuals of the linear fit;and the critically seismogenic region is finally defined as the circular region that minimizes the curvature parameter.Retrospective testing on 36 M > 5 earthquakes occurring in North China during the last 40years show remarkable enhancement of the LURR precursory anomalies with the optimal critical regions.From these statistics,we found that the optimal critical regions derived from both methods are consistent with each other:The slopes of the linear relationship between the radii of the optimal critical regions and the magnitude of the detection earthquakes for LURR and AMR are 0.34and 0.36,respectively.The results show that by combining different earthquake prediction methods,we can quantitatively assess critical seismogenic region scale and therefore provide information and constrains about the approaching criticality of the system.

    • Research on Coulomb Stress Change and Its Application in Seismology

      2013, 35(3):647-655.

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      Abstract:An earthquake is a natural phenomenon caused by the sudden breaking and slipping of crustal rocks when stress accumulates to a certain extent.The coseismic dislocations of a major earthquake not only cause stress state changes in adjacent areas,but also change the Coulomb stress.Earthquakes can be triggered by stress changes induced by other earthquakes;the most common examples are aftershocks.Static stress changes can increase or decrease seismicity in the surrounding regions.According to the Coulomb failure criteria,ΔCFSwill affect the failure condition of a fault.WhenΔCFSis positive,it will accelerate the speed of the stress rupture accumulation in the surrounding areas and cause the next earthquake to occur sooner,which is called stress triggering;on the contrary,whenΔCFSis negative,it will defer the accumulation.In recent years,seismic Coulomb stress changes generated by the earthquake and subsequent temporal relationships have been valued by seismologists all over the world.Studies have shown that a minor static Coulomb stress change of 0.1bar may trigger earthquakes and make the regional seismic activity change in the future.Therefore,it is important to explore the relation between Coulomb stress changes and earthquake triggering not only for the study of long-term earthquake prediction and static stress changes triggering subsequent seismic events,but also for future regional seismic hazard analysis.In this paper,the definition and the physical meaning of Coulomb stress are explained,and then the research progress of the applications of Coulomb stress change in seismology are discussed from five aspects:1)The triggering of aftershocks by a strong earthquake.Based on Okada’s([year\〗)elastic half-space dislocation model,the Coulomb stress change images are calculated,and then the spatial distribution of aftershocks are studied.The positive and negative Coulomb stress distribution images are related to the activity of aftershocks directly and affect the regional seismic hazard assessment;2)Triggering of the subsequent earthquakes by strong earthquake.The main way to trigger subsequent earthquakes is stress transfer,in which the stress before an earthquake event can have an effect on aftershocks;3)Stress shadow.A socalled stress shadow means the negative Coulomb stress changes an area with the function of inhibiting or delaying the fault slip and rupture with aΔCFS <0,which will either decrease the seismic activity or prolong the time of the next earthquake;4)The analysis of seismic activity;and 5)The related application of software.Though limited by the inability to accurately predict the time of subsequent earthquakes,Coulomb stress changes have been proven to be very useful in predicting epicenter locations.There is still much research left to be conducted to predict the location and timing of future earthquakes accurately by Coulomb stress changes.

    • Seismic Detecting for the Shallow Tectonic Features of the Xiadian Fault

      2013, 35(3):656-663.

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      Abstract:The Xiadian fault is a Holocene active fault in the north China plain.It exists from Pinggu in Beijing,to Mafang and Pangezhuang in the southwest,and it ends in Yongledian in the south.It is oriented towards NE 45°and the total length is 45km.Many scholars have studied the characteristics of the quaternary period activity on this fault,and of a magnitude 8 earthquake which happened in 1679.But the Xiadian fault is a complicated structure and the understanding of the shallow structural features of the fault are not entirely accurate.In this paper,the Xiandian fault is detected with high resolution shallow seismic exploration.The observation system contains 72records,a 4minterval,an 8mshot interval,18CMP stacking,and a unilateral trigger.A combination of a 60Hz vertical geophone and an 80kg rammer artificial lamping source are used,and each shot point was hammered on above 25times.The data acquisition parameters are:a sampling interval of 0.25ms,a recording time of 1 000ms,a 15Hz low cutoff frequency,and a 500Hz high cutoff frequency.Vista2D/3Dseismic processing software is applied for data processing.The following aspects are focuses of this study:careful removal of the primary wave,ensurence of the shallow reflection wave,consistent compensation processing of amplitude andsurface,suppression of interference,improved signal-to-noise ratio,consistent deconvolution of the surface,wavelet processing(in order to improve the resolution and fidelity),velocity analysis,residual static correction and good post-stack migration processing,and so on.Rich strata of the interface appear in the period of less than 700ms reflection wave group sections,according to wave group characteristics,and the profile can be roughly divided into two parts of the south and north.The strong reflections on the southern section are greater the reflection power is stronger with better continuity-while in the north the weak reflection energy leads to poor continuity.According to the characteristics of the rupture and the distortion in the seismic section,the entire section is divided into nine fracture structures by a breaking F5fault.The sections in the south and north display obvious differences:the southern section of the reflection in the phase axis is continuous and the layer is clear,while the north section of the reflection phase axis is messy.According to the characteristics of the seismic profile,nine tectonic faults were confirmed.From the time-depth conversion profile_______ comparison with the borehole data,the depths of faults'upbreakpoints were determined and the faults'activity periods were also determined.The detection results show that the fracture is composed of four faults,one of the main faults is still active and three new active faults were detected in the hanging wall of the fracture.According to the characteristics of Xiadian fault,it is a high dip angle fault to near the surface and the quaternary active fault zone.The results show that the Xiadian fracture structure is complex.

    • The China Loess Microstructure Types and Its Seismic Subsidence Zones Divided

      2013, 35(3):664-670.

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      Abstract:Loess forms from dust being deposited over the millennia under varied climatic conditions in the Loess Plateau of China through climate evolution.Influenced by monsoon,rainfall,temperature,dust characteristics,and so on.By forming under different regional climatic conditions,loess exhibits a wide range of microstructural morphologies.From its microscopic structure,we can obtain datum on particle size distribution,pore size distribution,and cementing quality,which can more fully elucidate the formation of regional loess.Because the microstructural characteristics of loess are directly related to dynamic deformation,strength,and arrangement mode,the features of loess microstructural formation types and regional deposition by particle size can be studied by an intuitive method in seismic hazard analysis.In contrast,in similar Midwestern shallow eolian loess soils(not considering landform),analysis of the microstructure under different soil environments is by sediment size.Western loess-forming microstructures are divided into five categories:(1)near a sand source,formed by fast sand dropping;(2)weakly formed by strong sand dropping;(3)formed in cold weather by slow sand dropping;(4)weakly formed in warm,damp weather;and(5)strongly formed in warm,damp weather.Differences in particle size,particle size distribution,particles between,degree of consolidation,contact,and so on,determine the microstructure types in the sediments,which have important effects on engineering properties.By analyzing the formation mechanism of loess by study of the microstructure in regional climates,and then further by analyzing the loess area,the regional differences in soil microstructure can determine the sediment deformation(either strong or weak).Such information is useful in building engineering site design and in determining corresponding protective measures.

    • Geochemical Features of Fault Gas on Northern Margin Fault of Xiqinling and Its Seismic Hazard Analysis

      2013, 35(3):671-676.

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      Abstract:The Northern Xiqinling fault zone is located at the northeast edge of the Tibet Plateau, which is one of the largest active faults in northern region of the plateau and the key earthquake hazard area in Gansu province.During the most recent decade,many large earthquakes have occurred in succession near the rim of Bayan Har Block,including the Mani MS 7.9earthquake on the western border,the KunLun MS 8.1earthquake on the northwestern border,the Wenchuan MS 8.0and Lushan MS 7.0earthquakes on the eastern border.The spatial and temporal variation characteristics of these seismic events show that the Bayan Har Block has entered a new period of seismic activity,which has enhanced the earthquake risk of the adjacent areas including the Qaidam and Qilian blocks.Therefore,continued research of seismic hazards and background fields of the Northern Xiqinling fault zone are necessary.In this study,we surveyed the spatial distribution characteristics of fault gas concentration on the Northern Xiqinling fault zone.The hazard area was predicted according to the spatial concentration anomaly values of Hg and Rn soil gas combining with the seismotectonic background and spatiotemporal evolution characteristics of large historical and recent earthquakes.We conclude that the tectonic background of large earthquakes at the F1and F4segments of the Western QinLing fault zone includes few small earthquakes,a lengthy period since the most recent large earthquake,and a low gas concentration of Hg and Rn.In comparison,the F3segment of the Northern Xiqinling fault zone showed frequent small earthquakes,a short period since the most recent large earthquake,and a high gas concentration of Hg and Rn.This research can provide vital background information for earthquake prediction.

    • Study on Focal Mechanisms of Moderate-small Earthquakes and Characteristics of Recent Tectonic Stress Field in the Anhui Sector of Tanlu Fault Zone

      2013, 35(3):677-683.

      Abstract (1134) HTML (0) PDF 1.06 M (1355) Comment (0) Favorites

      Abstract:The focal mechanisms of 239moderate and small earthquakes since 1970 in the Anhui sector of Tanlu fault zone were calculated with two methods:using the amplitude ratios of vertical P and SV waves in combination with the first motion of P,SV,and SH waves,and with 93focal mechanisms in the northern sub-sector and 146focal mechanisms in the southern sub-sector.Based on these abundant focal mechanisms,we have discussed in detail the earthquake fault types and the characteristics of the modern tectonic stressfield in the Anhui sector of Tanlu fault zone.The statistical analysis of the parameters of focal mechanism solutions shows that most moderate and small earthquakes occurring in the Anhui sector of Tanlu fault zone are of the strike-slip type,amounting to 54%of the total.Reverse faulting and normal faulting earthquakes occur less frequently,representing about 26%and 20% of the total,respectively.Azimuth and obliquity distribution of the P axis and the T axis are of obvious advantages,showing that the tectonic stress field in the Anhui sector of Tanlu fault zone and its sub-sectors is horizontally compressed in approximately the EW direction and horizontally dilated in approximately the NS direction.We further inverted the mean tectonic stress field in the Anhui sector of Tanlu fault zone and its subsectors with the force axis tensor computing method,and the results are as follows:in the Anhui sector of Tanlu fault zone,for the azimuth of maximum principal(compressive)stress axis(compression axis),σ1is 265°and its plunge is 6°;for the azimuth of the minimum principal(extensional) stress axis(tension axis),σ3is 356°and its plunge is 9°;in the northern sub-sector,for the azimuth of the maximum principal stress axis,σ1is 260°and its plunge is 4°;for the azimuth of the minimum principal stress axis,σ3is 350°and its plunge is 2°;in the southern sub-sector,for the azimuth of the maximum principal stress axis,σ1is 269°and its plunge is 8°;for the azimuth of the minimum principal stress axis,σ3is 1°and its plunge is 11°.These results indicate that the Anhui sector of Tanlu fault zone and its sub-sectors are horizontally compressed approximately in the EW direction and horizontally dilated approximately in the NS direction,which is in accord with statistical results of focal mechanism parameters.We analyzed the variation curve of the azimuth of maximum principal stress axis(σ1)versus time,which shows that the total variation trend of theσ1azimuth versus time is consistent between two sub-sectors of the Anhui sector of Tanlu fault zone,meaning both show the transition from clockwise deflection to counter-clockwise deflection in about 1998.Theσ1azimuth of the northern sub-sector experienced continued clockwise deflection from 1988to 1993,with deflected amplitude amounts to 23°,then the transition showed in 1994;a MS5.2earthquake in Cangshan,Shandong in 1995occurred after the transitions recovered,which is in accord with the variation of the trend of the P axis azimuth obtained by Zhou Cuiying([Year]),who used the method of composite focal mechanism solutions of moderate and small earthquakes.

    • Study on the Characteristic of Focal Mechanism Solutions of the Shanxi Reservoir Earthquake

      2013, 35(3):684-691.

      Abstract (1005) HTML (0) PDF 948.82 K (1082) Comment (0) Favorites

      Abstract:Using P wave first motions and the maximum velocity amplitude ratio of Pg and Sg waves,the focal mechanism solutions of the Shanxi reservoir earthquakes above ML 2.0were calculated.The time and space characteristics of the focal mechanism solutions parameters were obtained as follow:most of the main press stresses are North-south oriented,most of the main tensile stresses are East-west oriented,the stresses are almost horizontal,most of the slips of the planes are above 60°,and most of the faults are strike-slip type.Both of the azimuths of the Paxis have the trend of first deviation and then recovery before some MS4.0earthquakes.In the range from 27.66°to 27.69°N,focal mechanism solutions parameters have a good consistency.Most of the azimuths of the P-axis are 0±30°and 180±30°,and most of strikes of the plane are 45±15°and 135±15°.Most of the slips with focal depths deeper than 4km are between 70°and 90°.

    • Focal Mechanism of the M_S4.6 Yangqu Earthquake of June 5,2010,Determined from the CAP Method

      2013, 35(3):692-697.

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      Abstract:On June 5,2010,a magnitude MS4.6 earthquake occurred in the Yangqu region,which was located on the Shilingguan uplift between the Taiyuan basin and the Xinding basin in the Shanxi rift.This was a moderately strong earthquake felt in Yangqu and surrounding areas.The earthquake ruptured on the Shangendi fault,which controlled the tectonic activities in the east side of the Taiyuan basin.Based on the seismicity distribution,it appears that this earthquake was also located in the seismic gap of the Taiyuanbasin.To better understand the seismotectonics of this region,we relocated this event and further studied its focal mechanism based on the local broadband waveform data recorded by the regional seismic network in the Shanxi Province.In this work,the earthquake was initially relocated by means of the absolute relocating method,and then the focal mechanism and focal depth were determined by the"Cut and Paste" (CAP)method.We inversed the focal mechanism using waveforms in seven stations near the epicenter with high SNR ratios and clear P wave polarization,and the stations were evenly azimuthally distributed.The results of the focal mechanism and focal depth were testified by comparing the observed records and the synthetic waveforms.The results indicate that the Yangqu earthquake was a normal fault earthquake with a small percentage of strike-slip components.The best double couple solution is 213°,47°,and -161°for strike,dip,and slip angles,respectively,for one nodal plane,and 109°,76°,-44°for another.The moment magnitude was MW4.5,and the estimated focal depth was 17~20km,as determined by the CAP method and absolute relocation method,which suggests that this event was a shallow earthquake.The focal depth of the Yangqu earthquake was consistent with the relocation of small to moderate earthquakes in the Shanxi rift.The Yangqu earthquake occurred about 6km away from the Shangendi fault,which is the eastern boundary fault of the Taiyuan basin and is about 9.7km away from the Xizhoushan-Xilu fault,which is the western boundary fault of the Xinding basin.The focal mechanism of the Yangqu earthquake was dramatically different with the tectonic settings of the Shangendi fault and the Xizhoushan-Xilu fault near the epicenter.Based on the relocated location,the Yangqu earthquake should occur in the Shilingguan uplift.However,there is no evidence to show that the Shangendi fault and the Xizhoushan xilu fault extend into the uplift region;furthermore,there is no fracture that is consistent with the mechanism solution of the Yangqu earthquake.Thus,combining previous studies and our results,we suggest that the Shangendi fault and the Xizhoushan-Xilu fault are not the seismogenic fault of the Yangqu earthquake.Because the energy is too weak to transport the rupture to the surface,no surface rupture has been found in the field survey.Therefore,we suggest that a buried fault may be the seismogenic structure of this event.This conclusion still needs further investigationwith ambient noise imaging,active fault detecting,a dense network of high dynamicrange seismometers,and geological field work in Yangqu and its surrounding areas.

    • Analysis of the Characteristics of the Coseismic Response of the Gravity Instrument at the Qiongzhong Seismostation

      2013, 35(3):698-701.

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      Abstract:Far-field seismic-wave-induced fluctuation of water levels was first recorded in deep wells in Italy in 1899,and,since then,seismologists and hydrogeologists all over the world have been studying this phenomenon.Since the loading of the coseismic response has wide regional characteristics,its features are easily recognized.Today,since no breakthrough progress has been made in the study of seismic precursor mechanisms,the study of coseismic response is of critical importance for the understanding of earthquakes and their precursors. Interim characteristics of the wave,wave characteristics,and earthquake preparation process using the whole point semidiurnal tidal observation data can represent the solid earth tides well,but not the pre-earthquake short-term fluctuations due to the large-scale sampling rate increase,suggesting that the use of digital deformation observation data is preferable.Since short-cycle fluctuation and jumping occur before the earthquake,precursor short-impending information and co-seismic deformation information of global earthquakes are essential. In February 2013,six earthquakes occurred in the Santa Cruz Islands,and there was a coseismic response of the gravimeter at Qiongzhong.The coseismic response characteristics in three aspects of delay time of surface wave,the greatest deformation range and co-seismic duration were researched.In this paper,we study 6earthquakes in the Santa Cruz Islands on February 6,2013.Before an earthquake,the gravity instrument observation curve is smooth;the observational curve of the gravimeter at the Qiongzhong seismostation on Feb.6,2013denotes a strong earthquake(MS7.5),which shows a pulse-shape at the onset of pulsation,recorded at 09:22. (Beijing time)The response curve of the gravimeter reaches a low value by 09:44and rises gradually to a peak at 09:46,before returning to the original level,lasting a total of 42minutes.The result shows that the time delay of the surface wave is the same in earthquakes originating at thesame place.The duration of the coseismic response is related to the resolution ratio of the observation instrument;the amplitude of the coseismic response is positive correlated with the magnitude of the earthquake.The coseismic responses are mostly high-frequency impulses caused by surface waves,some of which had long periods.The strain-step changes and wave motions were caused by the arrival of the corresponding surface waves.The shape and size of the step changes and the response time recorded by different instruments were different;this difference is probably a reflection of different instrument properties,such as sensitivity and frequency response.The result may help us reach a better understanding of the performance of digital observation instruments,providing us a way to study the short-impending anomaly prior to earthquake.Further analysis and studies on focal mechanism of the earthquake is necessary to better understand the characteristics of gravimeter records for distant and strong earthquakes.

    • Empirical Relationship between Shear Wave Velocities and Soil Depths in Kashi City

      2013, 35(3):702-708.

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      Abstract:The shear wave velocity of soil is one of the most widely used parameters of geotechnical engineering investigation and seismic safety evaluation.It is indispensable for the determination of site classification and soil response calculation,and is also indispensable for calculating the predominant period of building site,judging liquefaction of sand foundation,test the result of foundation soil reinforcement treatment and elastic modulus.In this project,when there is no measured shear wave velocity according to the standard penetration value or the depth of soil layer using the statistical relationship for soil layer shear wave velocity,and with a large number of ongoing engineering constructions in the same city,the repetition of shear wave velocity testing not only affects the progress of the project,but also increases the project investment.Therefore,it is reasonable to assume that the empirical relationship between the soil shear wave velocity and the depth of soil,which will accelerate the construction of major projects in the process,has significant social and economic benefits.Since the 1970s,scholars at home and abroad(e.g.,Hardin[Year])that conduct research on the shear wave velocity of statistical relationships believe that the shear wave velocity and the depth of the soil layer have better statistical relationships,which can be mainly divided into three types of the power function,linear function and a polynomial.Kashi is an ancient border city of the western motherland with a history of over two thousand years.Kashi city decided in 2008to carry out the seismic microzonation.The working range was 105km2,in which 105drill holes were laid,and then more than 1600test points of the shear wave velocity were obtained.This work laid the foundation for the study on empirical relationship between the soil shear wave velocity and soil depths in Kashgar city.In this paper,based on statistical studies of the empirical relationships between the soil shear wave velocity and soil depth,according to the unit division of Kashi city landform,we described the formation lithology of different geomorphic units,collected shear wave velocity data of the seismic microzonation in Kashi city and nearby seismic safety evaluation,analyzed the shear wave velocity data.Then we used three statistics regression analysis method most commonly used today to give respectively the empirical relationship between shear wave velocity and soil depths of conventional soils such as silt,silty clay,silt,sand and gravel in two geomorphic units of alluvial plains in the south of the Ake Tagg mountain area(Ⅰarea)and alluvial plain of the Tuman River- Kyzyl River(Ⅱarea).Through statistical study we find that the fitting relationship ofⅡ-2's has a higher precision,and in fitting relationships,the power function model is primary,the polynomial is less important,and there is no linear statistical relationship.The analysis shows that the statistical formula of shear wave velocity and the depth of the recommendation is reliable,although there is no wave velocity test site for reference,providing the soil background information and analysis basis for the city of Kashi to implement earthquake disaster mitigation planning and soil seismic response analysis.

    • Type and Selection of the Ground Motion Attenuation Relations during Seismic Safety Evaluation

      2013, 35(3):709-714.

      Abstract (1660) HTML (0) PDF 1.07 M (2025) Comment (0) Favorites

      Abstract:Through the description of the evolution of attenuation relation,three types of attenuation relations are introduced(typeⅠ,typeⅡ,typeⅢ),with the differences among them including whether they contain the high-frequency ground motion magnitude saturation factor C3M2(a non-linear attenuation factor of magnitude M)and the acceleration near-field saturation factor C5eC6M(a distance factor).The origins and functions of two such factors are analyzed in this study.The ground motion increases with the increasing of M,but the amplitude of it rapidly decreases with the increasing of M.C5eC6Mplays a role in the seismic source body’s range scale,in which the ground motion varies not along with the distances’ change in the epicentral area.The combined effects of C3M2 and C5eC6Mstrongly inhibit the false information that the near-field ground motion is too large in the case of high-magnitude,so as to reach a level consistent with the actual situation.The acceleration near-field saturation factor C5eC6Mis the content that the attenuation relation must contain,because it contains the influences of the seismic source size and correlates with the actual observation data.In the seismic safety evaluation,C3M2item can be chosen according to the local seismic environment.Examples are presented to explain that the influences of C3M2 can be neglected and the attenuation relation without C3M2 can be selected during the seismic safety evaluation when thelocal seismic environment suffers from fewer influences due to the high-frequency ground motion;if the local environment has more influences,an attenuation relation with C3M2 should be selected.This essay chooses of a set of typeⅡand then a set of typeⅢto make a comparative analysisof the attenuation relation.In general,type III decays faster than type II.As the distance increases,the peak accelerations with the use of typeⅢare smaller than that with the use of typeⅡ.In addition,type III matches well with the actual records in the case of high-magnitude and short distance earthquakes,because it contains C3M2 .Therefore,in the evaluation of seismic safety,from a conservative perspective,the attenuation relation of typeⅢshould be used to evaluate the impact of potential seismic source zone at a short distance,and the attenuation relation of type II should be used to evaluate the impact of the potential seismic source zone at a long distance.This study uses the engineering sites of Kunming and Guiyang and the aforementioned typeⅡand type Ⅲattenuation relations to make calculations of a probabilistic seismic hazard analysis,with results that are consistent with the conclusions of the above analysis.

    • Key Laboratory of Loess Earthquake Engineering,CEA

      2013, 35(3):715-716.

      Abstract (1004) HTML (0) PDF 1.32 M (809) Comment (0) Favorites

      Abstract:

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