Abstract:As the transmission carriers of oil, gas, and water, buried pipelines are one of the important facilities in the field of underground engineering. With the increased usage of buried pipelines, those that are under the influence of transport medium as well as the soil and loading environment, especially metal pipelines, are prone to corrosion. After a major earthquake, a pipeline with existing corrosion defects can be prone to leakage and fracture accidents, resulting in a huge waste of resources, environmental pollution, and even the death of humans and animals. Therefore, research on the seismic performance of buried corrosion pipelines has become increasingly important. This paper examines buried pipelines and explores the impacts of pipeline corrosion depth, corrosion width, and corrosion location on the seismic performance of the buried pipelines. The purpose is to provide a theoretical reference for the safety and practicability of pipelines; provide guidance on the continued use, maintenance or replacement and safety of pipelines; and provide data to encourage further research on the seismic design of pipelines. This paper takes the actual project as the background and then analyzes the buried pipeline response under different parameters in the finite element software ANSYS using the seismic response displacement method.

Abstract:To guarantee the safety of a tunnel, a nonlinear numerical analysis of an earthquake is carried out by using the FEM software. The elastic model was used to model the characteristics of concrete tunnel under circulating load. The Mohr-Coulomb model was adopted for soils, and the artificial boundary was chosen as the boundary condition. For the purpose of comparing the responses of uniform waves, traveling waves, coherent waves, and traveling-coherent waves, artificial multi-point earthquake acceleration was encoded into the FEM model. Compared with the calculation results of consistent excitation, the analysis shows that non-uniform seismic excitation can significantly increase both the force and displacement of the tunnel, which can have adverse effects on the seismic performance of the tunnel. This research conclusion can provide scientific basis for anti-seismic design and further analysis of long-tunnel structures.

Abstract:The erosion of soil by scour around a pile weakens the lateral support in bridge foundations and this phenomenon has an effect on the seismic vulnerability of bridge pile foundations. Therefore, it is important to study the seismic fragility of bridge piles in the presence of scour. We used SAP2000 software to establish a three-dimensional finite element bridge model in the presence of scour. Damage occurs more readily at bridge piers and pile foundations and these components may become plastic during earthquakes. As such, we simulated these components using an elasto-plastic connection unit. We simulated the mechanical behavior of the soil using nonlinear p-y springs and modeled the loss of soil by removing the p-y springs above the scour surface. We selected 80 acceleration time histories of seismic waves that conformed to site II, and then translated the acceleration time history of each seismic wave into the displacement time history. We then applied the displacement time history to the p-y springs and carried out a nonlinear time history analysis on the bridge model. We obtained the seismic response of the bridge and recorded the maximum response of the bridge pile under each seismic wave. Using a probabilistic seismic demand analysis approach, we developed an analytical seismic vulnerability model of the bridge pile at different scour depths. We used curvature ductility as a damage index, and according to Hwang's suggestion, defined different damage states of the pile foundation. We obtained the boundaries of damage states by applying moment-curvature analysis to the pile cross section, thus obtaining quantitative data of the different damage states of the pile foundation. On this basis, we assumed that lognormal distribution functions were suitable for developing fragility functions, and we used regression analysis to estimate the parameters in the seismic fragility functions. We established the seismic fragility curves of the pile under different scour depths, and then discussed the influence of scour depth on the probability of the pile damage. The results show that with increasing scour depth, the probability of seismic damage to bridge pile foundations increases. Therefore, special attention should be paid to the adverse influence of scour when designing earthquake-resistant bridge pile foundations.

Abstract:During pile driving, soil plug effect evaluation has an important influence on the prediction of pile driving resistance and bearing capacity. The static equilibrium method is usually applied to determine the plugging status of a steel pipe pile with a small diameter. Steel pipe piles that are larger than 2 m have been widely used to increase the operating water depth of offshore platforms and to construct offshore wind projects. The stress and deformation characteristics of soil in pile tube change with the increase of pile diameter. Soil failure mode in the process of driving in sand, with steel pipe piles of different diameter to length ratios is obtained by using numerical simulation method. Based on the numerical simulation result, the Meyerhof formula is determined to calculate the soil resistance. To examine the soil plug effect of a large-diameter steel pipe pile, the quasi-static equilibrium method is proposed, in which the influence of the inertia force on soil plug is analyzed. According to the small-scale pile driving model tests with different diameter to length ratios and the analysis of practical piling project, the applicability of the quasi-static equilibrium method for a large-diameter steel pipe pile is verified.

Abstract:This paper develops a new control module for a hollow cylinder apparatus (HCA), which allows principal stress to rotate back-and-forth at any angle. A series of experiments on Toyoura sand are conducted. The results indicate that the effects of both the amplitude of the rotation angle and the initial direction of the principle stress on the deformation of sand should not be ignored. Furthermore, sand may expand when principal stress rotates back-and-forth due to the "wedging effect". However, this will not happen when principal stress rotates continuously.

Abstract:Earthquakes are an important factor in inducing slope failure and the anti-slide pile is an important slope-control engineering measure. Therefore, the study of the mechanism of the anti-slide pile during earthquake activity has important engineering significance for slope protection. Previously, the action mechanism of the anti-slide pile has been mainly studied under static loads and there is a lack of research regarding the pile's response to earthquake activity. Many factors must be simplified when using the two-dimensional analysis method, which affects the accuracy of the results. Taking a project in Meizhou city, Guangdong province as an example, we used ABAQUS software to establish a three-dimensional model and then analyzed the mechanism of the pile-soil effect under earthquake activity. The results show the following:(1) Under earthquake activity, the horizontal displacement of the upper part of the slope is relatively large, with a maximum value of 87.05 mm. (2) Under earthquake load, the stress on the anti-slide pile is far greater than that prior to the earthquake:the maximum value under static loads is 147.24 kPa, and the maximum value of the pile body during an earthquake can reach 326.36 kPa. (3) The strain on the anti-slide pile during an earthquake is much larger than that under static loads:The maximum strain under static loads is 4.63×10^-5 and the maximum strain of the pile during an earthquake is 34.10×10^-5. Therefore, in practical projects, the strength and stiffness of the pile should be taken into account to determine the need for reinforcement of anti-slide piles subjected to earthquake activity. These research conclusions have direct significance on the prevention and control practices adopted in slope engineering projects.

Abstract:In this study, we used the dynamic time history method to analyze the seismic response of bridge structures. The time history analysis method, which has higher accuracy than the response spectrum method, can identify various kinds of responses and can also consider various factors in the calculation and analysis, including the coherent effects, multi-dimensional inputs, and multi-dimensional responses. The primary problem in applying the dynamic time history method is how to simulate ground motion acceleration. In the artificial acceleration wave, the velocity and displacement of the seismic wave deviate from the baseline. At the end of the seismic wave, the velocity and displacement time history are not zero, which generates a baseline drift of the seismic wave. As such, it is necessary to revise the seismic response before analysis and to eliminate the influence of the baseline drift phenomenon. At the same time, the response spectrum of the acceleration wave before and after correction must be checked and compared. In this paper, based on a 2D coherent model, we analyze the seismic response of a wide long-span bridge structure under multi-point excitations of a random earthquake motion field. We use the polynomial fitting method to adjust them in the time domain. We use the response spectrum to check the seismic wave, which is corrected before and afterwards. Then, taking a large-span self-anchored suspension bridge as an example, we use the linear time history analysis module in the finite element analysis software and the synthetic seismic wave to analyze and compare the seismic response results under uniform and multi-point excitations. The results indicate that the artificial acceleration wave must take into account the baseline drift phenomenon, and the polynomial fitting method can be used to adjust the waves. In addition, the seismic waves corrected before and after must be checked against the response spectrum. For large-span and wide bridge structures, the non-uniformity of transverse seismic waves must be taken into account.

Abstract:With the numerous catastrophic incidences of progressive collapse in the past, there has been increasing interest from both engineering and academic communities toward evaluating the ability of reinforced concrete (RC) structures to resist progressive collapse. Progressive collapse of structures under earthquake and explosion problems induced a major threat to people's life and property. It is a hot direction in the research of civil engineering. The majority has focused on scenarios in which a single vertical loading bearing member, such as a column, is removes. This paper adopted the same method. In order to improve the integrity of structures with prestressed concrete hollow core slabs and to prevent vertical support member failure or progressive collapse, the joint between slabs were studied in this paper, this study aims to assess the effects of vertical support removal on the overall performance and load resisting mechanisms of RC structures. In this paper, two prestressed hollow-core slabs are studies with the condition of concentrated loading by two points symmetrically, specimens is jointed by two short prestressed hollow-core slabs, then cast-in-place concrete grouted. Joints have two types, transverse direction by butte connection with U-shaped tendons and out of prestressed reinforcement, longitudinal direction by tie connection with planting bar and out of prestressed reinforcement. All specimens have the same span of calculation. This article used the quartile static loading method to research the new type of continuous slab prefabricated. In the process of loading suddenly dismantle intermediate support. The test results collected included failure modes, load resisting capacities, deformation capacities, strain gauge results, vertical movement of support. The suspension mechanism was analyzed during mechanical process of specimen. Finally the author comes to the conclusion that the arrangement of side beam and plate joints is reasonable,Appropriate peripheral and transverse joints in new type of prefabricated floor can achieve ideal collapse resistance。

Abstract:In order to investigate the dynamic responses and damage distribution of low layers of masonry structures in village buildings during strong earthquakes, finite element models of masonry structures are established on the ABAQUS software program based on the survey and the material test of rural buildings; the analysis considered the different details of seismic design. The vibration characteristics, displacement response, and the damage configuration of each model are then compared based on the results of dynamic characteristic analysis and elastic-plastic time-history analysis. Research results show that the vibration regularity and model are not changed by the reasonable setting details of seismic design in low layers of masonry structures. Nevertheless, the structural column is involved in the anti-lateral work to some extent, such that the basic period of the structure is slightly decreased. The dynamic displacement responses of structures are efficiently restricted by the column in the elastic period, and the energy dissipation capacity of masonry structures can be improved in the plastic period. However, the imbalance between longitudinal and lateral stiffness could be exacerbated once the structure stiffness is degraded. When a structure comes up against a major earthquake, the seismic performance can be improved effectively by the structural column and ring beam; for example, the development of cracks in the bearing cross-wall can be inhibited, and the roof damage can suppress the bearing failure, thereby weakening the torsion effect.

Abstract:To date, the high frequency scattering law of seismic waves in sedimentary river valleys has not been established. In this study, we adopt the high-precision indirect boundary element method (IBEM) in a two-dimensional broadband analysis of P, SV, and Rayleigh waves. The numerical results demonstrate that the IBEM is effective and accurate in simulating seismic wave broadband scattering. In low and medium frequencies (dimensionless frequency η><5.0), the seismic wave amplification effect in valleys is significant, and it attenuates at high frequencies (η>10.0) and even exhibits a necking effect. In terms of surface displacement amplitude, with a decrease in the incident angle θ, the maximum ground displacement amplitude shows a gradual decreasing trend. The surface displacement amplitude changes more dramatically with increases in the incident frequency η. Meanwhile, the focusing effect of seismic waves in sedimentary valleys also has a significant impact. When the incident wave frequency increases, the sedimentary valley displacement amplitude variation range of the valley terrain is more intense. With an increase in the valley depth, the bandwidth in the displacement amplification frequency gradually decreases, with the frequency at first peak decreasing and the spectrum curve strongly oscillating at low frequency. With an increase in depth of the sedimentary valley, the bandwidth of the displacement amplification spectrum decreases, the frequency at the first peak is reduced, and in the low frequency band, the spectrum curve is sharp. The damping ratio has a significant impact on the surface displacement amplitude of the sedimentary valley, which clearly attenuates, especially at high frequency. To more scientifically interpret earthquake damage and to better evaluate seismic safety, seismic response analyses of actual sedimentary valleys must take several factors into consideration, including wave type, incident frequency, and angle, as well as the depth-to-width ratio of the valley.

Abstract:The inversion of ground motion, a strong stochastic process with both amplitude and frequency dual nonstationary characteristics, is very difficult. Thus, finding a nonstationary ground motion modeling method that can simultaneously simulate ground motion characteristics and determine actual ground motion time-varying distribution characteristics has become an important endeavor in ground motion research. A genetic algorithm and quadratic optimization identification technique based on the Kanai-Tajimi power-spectrum filtering method proposed by Du Xiuli et al. are employed to improve the bimodal time-varying modified Kanai-Tajimi power spectral model and parameter identification method proposed by Vlachos et al. Additionally, a method for modeling time-varying power-spectrum parameters for ground motion is proposed. This method is ideal for improving the Kanai-Tajimi spectral model of earthquakes because it satisfies the requirements of high-and low-frequency power spectra by filtering the Kanai-Tajimi spectrum with a series of high-and low-pass filters. The nonstationary ground motion simulation method uses two random variables to accurately capture the second-order statistics of the original stochastic process by Liu Zhangjun, thereby providing an efficient and convenient approach for subsequent verification. The results of a Chi-Chi ground motion example verify that the improved bimodal time-variable Kanai-Tajimi nonstationary stochastic model shows good feasibility and effectiveness. The results of the present research provide an important reference for designing seismic waves during seismic analysis of major engineering structures.

Abstract:The pore structure is an important characteristic of loess that helps distinguish it from other soil types. The macroscopic mechanical behaviors of loess, such as its collapsibility and seismic subsidence, are closely related to its pore structure. In this paper, we develop a method combining Matlab and Image-Pro Plus (IPP) software to pre-process images of the loess microstructure. Qualitative and quantitative analyses of intact loess samples taken from Xining in Qinghai, Yongdeng, and Lanzhou in Gansu, Xiji in Ningxia, and Ruicheng in Shanxi are also performed at the microscopic level. Microstructural image processing is introduced, and a new method to determine three-dimensional porosity based on gray scale calculation is proposed. Results indicate that the microstructure of the Q₃ loess in different regions is closely related to the regional, depth, and climatic conditions. In qualitative analytical tests, loess particles in the area near and esat of Liupan Mountain were given priority to with grains and grume because of its rich rainwater. The climate in the western region of Liupan Mountain significantly differs from that in the east; specifically, the western region is more arid and shows a smaller contact area between particles and tendency to form trellis pores. In the test of quantitative analysis, the large pore content increases gradually from northwest to southeast in the space. Particles move closer to each other, and the distance between grains decreases with increasing depth from top to bottom; thus, the large pore content is gradually reduced. In-situ stress gradually increases, and loess particles and pores appear to rotate and deform because of squeezing with increasing of stratum depth. The elliptical ratio of medium and large pores decreases, and macropores change significantly. The soil is remodeled, and an orderly pore arrangement is achieved. Pore size and area are relatively uniform in each region, fractal dimensions and probability entropies decrease, and the rose curve is gradually smoothened.

Abstract:In this paper, the initial marsh-time or fluidity (MF), loss rate of fluidity as time (FL), saturation point (SP), setting time (ST), and bleeding rate are considered simultaneously to evaluate the compatibility between a polycarboxylate high-performance water-reducing (HPWR) agent and cement. The comparisons of these parameters between tested concrete and reference cement are conducted, and the corresponding membership functions are established. Then, the fuzzy mathematical evaluation method based on Matlab is used, and the limitation of reference cement is broken, resulting in a more comprehensive and accurate evaluation. Both the premixed concrete and the cement paste, which use the same polycarboxylate HPWR agent, are evaluated as "the best" by the method proposed in this paper, and the consistency is acquired according to the performance experiment. Results also show that they have good correlation. The research findings can serve as guidelines in the preparation of green concrete made of HPWR agents.

Abstract:The settlement of a soft-soil foundation due to earthquake is a considerable threat to buildings. To accurately calculate this settlement, a great number of studies have been carried out regarding the deformation characteristics of soft soil under dynamic loading, and a variety of empirical formulas have been proposed. These formulas, however, are not easy to apply by engineers without specific training because there are a large number of parameters and the experiments are complex. Based on the results from drilling sampling, wave velocity tests, and indoor static and dynamic triaxial tests, we obtained the static and dynamic parameters of 16 soil specimens at nine different depths in the coastal region of Tianjin, which experienced a large settlement following the 1976 Tangshan earthquake. We grouped the specimens into three categories with respect to their components and density, and used relatively simple models and the least squares method to fit the change law of the residual strain and the degradation index of the specimens. The research results show that:(1) The density of soft soil can be used to determine its composition and dynamic characteristics, and also as a main parameter to establish the relationship between the static and dynamic characteristics of soft soil. (2) Silty soil and shell interlayers can increase the modulus of soft soil. To obtain accurate parameters, the soil layers should be classified carefully before performing experiments. (3) The experimental results suggest that exponential models are advantageous when doing regional research on the deformation characteristics of soft soil under dynamic loading. (4) Dynamic loading has little influence on the degradation index of soft soil. In addition to these results, this study also provides some references and basic data for future research on the dynamic characteristics and seismic settlement of soft soil.

Abstract:In this paper, we design and complete a shaking table model test with respect to slope with a scale of 1:100, and discuss the similarity relation of the model, sensor layout, and process of model construction, as well as the seismic wave loading system. We built the model slope in soil with a height of 50 cm, length of 100 cm, and thickness of 45 cm, and performed a series of tests with inputs of different seismic wave types, amplitudes, and frequencies. We discuss the dynamic characteristics and responses of the slope in an earthquake and the influence of the ground motion parameters. The results show that the acceleration responses at the same slope position have obvious differences under different seismic loading inputs. The amplification coefficients of acceleration along the slope surface and in the vertical direction increase smoothly with increasing elevation, and otherwise increases dramatically in the slope body. At the same time, the input frequency of seismic waves has obvious effects on the dynamic slope responses. As it approaches the natural frequency of the model slope, the amplification effect of acceleration is clearly enhanced with increasing frequency. The amplification coefficients of acceleration on the slope surface are larger than those in the slope body at the same elevation. The amplification coefficients of acceleration decrease with increasing earthquake amplitudes. With an increase in vibration number, the damping ratios increase, and the amplification coefficients of peak acceleration in the slope decrease with increases in the seismic amplitudes. Based on the shaking table test results, we present the influence of the ground motion parameters on the dynamic slope characteristics. The acceleration amplification coefficients increase nonlinearly as the elevation increases, and the distribution of acceleration in slope changes as the input seismic wave frequency changes. Acceleration amplification coefficients increase with increments of seismic wave amplitude, but amplitude does not change the distribution of acceleration in the slope body. The duration time of the input seismic wave has little influence on the distribution and amplitude of acceleration in the slope. These results help reveal the mechanism of slope instability during earthquakes, and can provide valuable references for aseismic slope engineering design.

Abstract:Diurnal variation is an important part of the geomagnetic field. In this study, observation data was collected from 2011 to 2013 at three stations (JYG, LZH, and TSY) in the Gansu province. The data focused on time series characteristics of the Hurst exponent of geomagnetic Z-component diurnal variation. The results show that the variation range of the Hurst exponent at JYG and LZH stations is 0.08 and 0.06, respectively. This represents a normal change because the low point is in the middle of a year and the peak point is at the end of the year, completing a change cycle within a year. The change is similar between JYG and LZH stations. In 2012, there was a change in the Hurst exponent exceeding the normal range. On July 22, 2013, the M_S6.6 earthquake occurred at the junction of Minxian and Zhangxian in the Gansu province, 130 km from Tianshui city. The abnormal change of the Hurst exponent at the TSY station may be the result of a magnetic field change induced by the transfer of local, deep thermal mass in the earth. In combination with other research, this may provide an early indication of the Minxian M_S6.6 earthquake. This study provides evidence for further study of the mechanism of geomagnetic diurnal variation anomalies, seismo-magnetic relation, and earthquake prediction.

Abstract:In this study, we inverse 19 focal mechanism solutions of the foreshock, mainshock and aftershock events in the M_S7.1 Yushu earthquake sequence by the method of CAP. The results show that the 19 focal mechanism solutions are mainly strike-slip types, and the fore shock is similar to the main shock which reflects that the intimate relationship between the two events.The focal depth concentrates on about 7~12 km,and two aftershocks with the most shallow (4.5km) and deepest (34 km) facal depth significant thrusting and exhibited obviously boundary feature.The Epicenters of 19 events distrbute in the Yushu-Longbao fracture which is the northern branch of Ganzi-Yushu fault and it has been proven that the Yushu-Longbao fracture is the seismogenic structure of Yushu earthquake. Following the SE-NW direction along Yushu-Longbao fault pull a cross-section to observe the change of focal depth along the profile, we can see that the focal depth of Northwest section of Yushu-Longbao fault is greater than the southeast section, and this part is the main part in the late aftershock activity,so that the aftershocks have extended deep crust in the late seismic activity and the fracture-accumulated strain can be further released. The dominant distribution of P axis azimuth is 220°~230°while T axis azimuth is 310°~320°,and the two distributions are vertical to each other. It is found that the regional stress field is relatively uniform by analyzing the data of the focal mechanism solutions of historical earthquakes and GPS, which shows that the M_S7.1 Yushu earthquake is the normal release of the energy in the Earth.

Abstract:InSAR technology can achieve centimeter-level accuracy in terms of coseismic deformation measurement but presents disadvantages of complex data post-processing and consequent explanation. The results of GIS spatial analysis are extremely rich, and its data management function is fairly powerful. This paper's main objective is to use GIS technology to analyze the results of InSAR data, strengthen results management, and improve the preciseness of analytical results to enable a diverse display of the consequent data. A M_W6.3 earthquake that occurred at 16:30 on October 6, 2008 in Damxung County in the Tibet Autonomous Region is taken as an example. Using ENVISAT ASAR level 0 and SRTM DEM data groups, the coseismic deformation field of the earthquake was obtained via two-pass differential interferometry with the InSAR method. The basic geographic data of the study area, including river, boundary line, and road and boundary conditions, were collected. GIS data analysis capabilities were adopted to explain the seismic deformation field extracted by InSAR data. Using the GIS management function, effective management was first conducted on the multi-source data, after which the epicenter position of the earthquake was confirmed. Then, the maximum deformation quantity at the settlement area was obtained, and the main deformation zone was determined. Finally, using the GIS multiple display function, the deformation results were displayed in the form of statistical tables and sectional and three-dimensional drawings. The deficiencies of the InSAR data were related data post-processing, data explanation, and presentation achievement. Analysis of the InSAR results using GIS effectively compensated for the deficiencies of InSAR. GIS is suitable for extracting information on InSAR deformation fields and can effectively ensure the preciseness of the obtained results, thereby improving research findings in this field.

Abstract:Since 2007, component borehole strain observations have been carried out in Qinghai province. Because the observation environment is characterized by low interference levels and the observation instrument is stable, the observation data is continuous and reliable. During the observation period, several earthquakes with magnitude>6 occurred in Qinghai and the region nearby. To study the earthquake reflection ability of the borehole strain observation data, in this study, we analyze the observation data recorded by six 4-component borehole strainmeters in Qinghai from two aspects:the presence of anomaly prior to earthquakes and the coseismic characteristics. Our results show that the amplitude of the coseismic response of the 4-component borehole strainmeter bears a relationship to the magnitude and epicentral distance. In individual earthquakes, we found the coseismic response amplitude of multiple instruments to be inversely proportional to the epicentral distance in most cases and proportional in a few cases. The amplitude of the coseismic response of a single instrument is proportional to the general magnitude, whereby the larger is the earthquake magnitude, the greater is the amplitude of the coseismic response. The coseismic response delay time of the 4-component borehole strainmeter is mostly proportional to the earthquake epicentral distance, whereby the greater is the epicentral distance, the longer is the coseismic response delay time. The coseismic response duration of an instrument is basically proportional to the magnitude, whereby the greater is the magnitude, the longer is the duration of the coseismic response.

Abstract:The Cangshan M_S5.2 earthquake, which occurred on September 20, 1995, was one of the largest earthquakes of the past century in southern Shandong Province and inflicted huge financial losses. As it was also a significant example of the new active phase in North China, it is necessary to determine the seismicity and potential seismic hazard in the areas affected by this earthquake. Earthquakes are natural phenomena caused by fault movement when stress accumulates to a certain extent. Coulomb stress change occurs due to coseismic dislocations and visco-elastic relaxation after an earthquake. Research shows that a small change in the Coulomb stress can trigger an earthquake. In order to calculate the Coulomb stress changes of the Cangshan earthquake and their influence on surrounding faults, in this paper, we use field investigation results in a multi-layered visco-elastic model to determine the Coulomb stress changes from the coseismic dislocations and visco-elastic relaxation following the Tancheng and Cangshan earthquakes. We also discuss the triggering relationship between the two earthquakes, the influence of the aftershock distribution features of the Cangshan earthquake, and the influence of stress on the surrounding area. The results show that:(1) The Tancheng earthquake changed the conditions of failure in Cangshan, and the Cangshan earthquake was delayed by the Coulomb stress change (-3.23 bar) caused by the Tancheng earthquake in this area. (2) By analyzing the relationship between the Coulomb stress changes caused by the Cangshan earthquake and the aftershocks distribution, we found most of the aftershocks to have been located in regions where the Coulomb stress increased 0.08~0.12 bar. (3) With respect to visco-elastic relaxation, the calculation results show the Tancheng and Cangshan earthquakes to have had a significant influence on nearby faults. The northeast Anqiu-Junxian fault, the middle of the Cangni fault, the east Fushan fault, the Hanzhuang fault, and the Yicheng fault are all located in regions where the Coulomb stress has increased (≈5 bar), and there the potential for strong seismic hazard in these areas.

Abstract:We present a new three-dimensional model of the crustal P-wave velocity structure of the southeastern margin of the Taihang Mountains fault zone, which we developed by inverting 14 078 arrival-time data recorded by a local seismic network from 1981 to 2012. The results provide important new insights into the deep structure environment of the research region. The tomographic images show that the velocity distribution can be used to describe the characteristics of the surface topography and geologic structure at shallow depths, while in the deeper crust, the velocity distribution exhibits obvious lateral variation characteristics. The results for depths of less than 12 km represent the northern study area where the Taihang Mountains crustal uplift is located, which is mainly characterized as a high-speed zone. However, the southern settlement area of the low-speed zone and the results for depths greater than 12 km exhibit reversed characteristics. The velocity sections reveal that the velocity anomaly is roughly in line with the direction of nearby active faults. Based on the velocity profile, we determined the crust in the study area to be layered such that it could be divided into three layers, with the upper crust having a depth of 10 km. With respect to the lateral velocity change, there is little variety in the upper crust, but great variety in the middle and lower crusts. Earthquakes are mainly distributed in the range of 4 km to 20 km depth in the crust. On the basis of our analysis of the relationship between the velocity, faults, and strong earthquakes, we speculate that our study area has the necessary preparation conditions for the occurrence of a strong earthquake.

Abstract:On November 23, 2015, an M_S5.2 earthquake occurred at Qilian county, Qinghai province. By the end of the first day of December, 48 aftershocks had occurred in the mainshock seismic region, including 34 M_L1.0~1.9 aftershocks, ten M_L2.0~2.9 aftershocks, and four M_L3.0~3.9 aftershocks, with the greatest magnitude being M_L3.4. In this paper, based on the seismic network data of Gansu and Qinghai provinces, we use the cut-and-paste method to calculate the focal mechanism solution of the Qilian M_S5.2. We then use the waveform fitting method for synthetic and observed seismograms to further determine the focal depth of the earthquake. The results indicate that this event occurred on a rupture plane (strike 109°, dip 58°, and slip 21°), which demonstrated a left-lateral strike-slip mechanism with a minor reverse-faulting component, a moment magnitude of M_W5.16, and a centroid depth of about 9 km. The other nodal plane was characterized by a strike of 8°, dip of 72°, and a slip of 146°. The focal mechanism, which describes the nature and source of the rupture process, provides an important foundation for understanding the stress state of the source region and the earthquake faults, and for analyzing the causes of a seismic event. A comparison of the maps of focal mechanism solutions for the Qilian M_S5.2 earthquake and historical earthquakes illustrates that the focal mechanism of this earthquake is in keeping with historical focal mechanisms. Therefore, based on our comprehensive analysis, we can identify the middle of the north Tuoleshan active fault as the seismogenic structure of this event.

Abstract:This paper aims to work out a one-dimensional velocity model for Gansu area with a large amount of seismic data gained by the digital measuring seismic technology. Specifically, this study does classification and fitting calculation to get a one-dimensional velocity model, using the data of seismic phase of all the earthquakes happened in Gansu province from the period between January, 2009 to June, 2016. The purpose of classification is to show the influence of the results of fitting calculation on the seismic data, and the results show that fitting of a few closely approximates of all the earthquakes. Because there are many recording stations for major earthquakes and their epicentral distances are well-distributed, major earthquakes are chosen to be the objects of the study. On the basis of the preliminary results of the new model through the fitting calculation, we relocated 142 earthquakes that azimuths are well-distributed and seismic phases are clear by Hyposat program to calculated the depth of Moho surface. We also reference other models such as Ganqing Model,Crust1.0 and the averaging model of Gansu and the Acceptance Function are applied as references. After this calculation, a Hyposat batch processing of iterative localization is done within the scope of disturbance gained from the comprehensive calculation. Finally, based on the 8640 computations of the model and several residue contrasts, a model with minimum residue has been chosen as the new model. The newly-made model is basically consistent with the Ganqing Model, with just a few parameters different. The new model is applied to the location of 142 earthquakes, relative to Ganqing model the average residual reduced 0.05. The model is a large range of average results that cannot be applied to all earthquakes. According to the selected 142 earthquake distribution location weight, the model is more suitable for the southeast region of Gansu. In order to test the availability of the model, the model will be used in the daily cataloging process of Gansu seismic network, calculation results are obtained by a huge amount of data, the inspection also need plenty of seismic data. At present, the Gansu seismic network has used the Ganqing model and the new model at the same time, and make statistical two model's positioning accuracy in different region and with different magnitude.

Abstract:In this study, a numerical solution for a 2-D fault site model under incident P waves using the explicit finite element method combined with transmission of artificial boundary condition was derived. The distribution rules of peak ground acceleration (PGA) and the spectrum characteristics influenced by fault characteristics such as width and shear wave velocity of the fault and the incidence angle of the seismic waves were discussed. Numerical simulations shown that transform SV waves developed in the low velocity fault zone (LVFZ) when it struck by external incident P waves, and many trapped waves obviously developed in it. This result implied that the external incident seismic radiation congregated in the LVFZ, and the agglomeration effect increased with the increased width and decreased shear wave velocity of the LVFZ. Vertical LVFZs blocked the spread of oblique incident P waves, and the isolation effect decreased with the increased incidence angle of P waves. The seismic response of a variety of LVFZ models with different width and shear wave velocity struck by external vertically incident P waves was determined, and the results implied that the ground motion amplification characteristics in the near fault zone site are frequency dependent. The higher frequency components of ground seismic waves are obviously amplified by LVFZs with narrower widths and higher shear wave velocities, while the lower frequency components of ground seismic waves are obviously amplified by LVFZs with wider widths and lower shear wave velocities. In other words, the site amplification coefficient is frequency dependent, such that the widening the width or decreasing the shear wave velocity of fault fracture zone, the predominant frequency of a larger site amplification coefficient is becoming lower.

Abstract:Based on the teleseismic SKS phase recorded by 43 permanent broadband stations in Gansu Province in the northeastern margin of the Qinghai-Tibetan plateau, this study obtains the splitting parameters of the fast-wave polarization direction and delay times at each station using the minimum energy and rotation-correlation methods. The results can be summarized as follows. In the southeastern region of Tarim Basin, the fast-wave polarization sites exists obvious angle with the strike of regional faults, and coincides with the subduction direction from Tarim Basin to Qaidam Basin. This result reveals that the upper mantle deformation is mainly affected by ancient tectonic movement. The anisotropy observed may be considered "fossil" anisotropy. Because of crust-mantle delamination, decoupling between the crust and mantle occurs in this area. In the Qilian-Hexi Corridor region, fast-wave polarization shows a NW-SE trend, consistent with the strike direction of the main faults in this region. Comparison of the fast-wave direction with the direction of lithospheric extension and GPS-observed velocity reveal that the deformation model of the crust and upper mantle may be vertically coherent deformation. In the northern fringe fault of the western segment of the Qinling mountains, slow-wave time delays exert significant anisotropy in the vicinity. This phenomenon could indicate upper mantle deformation, which is caused by both deformation of the lithosphere and flow of the asthenosphere. In the Ordos block, the fast-wave direction shows a NW-SE trend, which suggests that the movement of deep material exists motion of flow around the Tibetan plateau. Collision between plates causes thickening and uplifting of the western China crust and eastward extrusion of material in the northeastern margin of the Qinghai-Tibetan plateau. Different regional stations present different levels of anisotropy in the northeastern margin of the Qinghai-Tibetan plateau, which further proves the complexity of tectonic deformation in its northeastern margin. According to the splitting parameters of SKS waves, the anisotropic characteristics of the study region are analyzed to investigate dynamic processes in the area.

Abstract:The rapid development of the strong motion network in Hebei province has resulted in 48 new stations being added to enhance the seismic monitoring capacity.Each station is equipped with REFTEK 130-REN-3 as the digitizer and SYSCOM MS2007+ as the accelerometer.Since the implementation of the project,a strong motion observation system has been established,which is relatively independent from the existing seismic network.It relies on heavy maintenance by engineers.Therefore,the problem of how to integrate the two systems and improve the efficiency of the network maintenance tasks has become urgent and is a key issue of concern.The integration of the systems requires a two-level approach,data integration as the foundation and application integration as the superstructure.In this paper,the application of instrument health data is introduced as an example.First,a model of health data integration is proposed.This model includes three layers:the data,middleware,and application layers.The data layer is the bottom layer and supplies health data to the upper layers from both the relational database and the Ethernet stream.The middleware layer is in the middle of the model;it shields the differences among the underlying data and provides a unified upward interface.It contains three components:message producer,message middleware,and message consumer.The message producer receives health data from the under layer,creates JMS messages,and sends them to the message middleware.The message consumer receives the JMS message from the message middleware,decodes the message into data,and sends them to the upper layer.The application layer is the top layer and through application integration it provides users with a unified graphic user interface.Second,the design and implementation of health data application integration into seismic and strong motion instruments is introduced.An application integration framework that comprehensively integrates several advanced technologies including Java EE,message pushing,and WebGIS is proposed.Software is introduced,which supports functions,including station map browsing,station health monitoring,and station database management.The software is developed under a Windows 7 environment with MyEclipse 6.0 as the IDE,Tomcat 6.0 as the web server,ActiveMQ 5.5 as the JMS broker,Geoserver 2.5 as the WebGIS server,MySQL 5.1 and PostgreSQL 8.4/PostGIS 1.5 as the database server.It was found to be functional,practical,high-performance,and with a friendly-GUI.Its utility will help improve the efficiency of maintenance jobs at the seismic network.It is also a demonstration of comprehensive network integration and development for similar applications.

Abstract:With the continuous advancement of seismic exploration and an expansion in the range of human activities,areas of exploration and associated surfaces have become increasingly complex to negotiate when acquiring seismic data.In addition,areas of exploration have now been expanded to urban areas,oil areas,pipelines,and other places where there are a variety of obstacles,which results in the need for complex seismic operational methods,and involves greater operational difficulty and lower work efficiency.During seismic data acquisition of complex transition zone (TZ),the obstacles are usually numerous,and the work area often contains intricate pipelines,wells,power grids,buildings,and areas under nature protection.In addition,mixed excitation methods are required,such as vibroseis,explosives,and different kinds of air guns.With the continuous increase in awareness of seismic operational safety and environmental protection,the valid acquisition area of seismic projects has become increasingly narrow,and the range of source point deployment has increasingly reduced.These factors are leading to the acquisition of poor quality seismic data,and even data gaps in some areas.There is an urgent need to determine effective acquisition space to reasonably lay out source points.Optimization of geometry,and excitation and receiving parameters improve seismic data quality,and although the use of data interpolation can compensate for missing data during later processing it is associated with "false" suspects.During actual operations,safe distance values are usually provided by clients or determined using instrument tests.However,safety distances are generally too large,and thus the effective acquisition space is greatly compressed.Based on above two points,this paper uses Sadov's vibration formula,known in engineering blasting,for seismic exploration,and combines flexibility of testing instruments and scientifically calibrated safety distances,thereby improving the capacity of the source layout,which further expands the seismic acquisition space,improves the quality of seismic data,ensures the safety of operations,and enhances the operation schedule.The research provided in this paper is thus of considerable use for seismic exploration in complex areas.