Abstract:Considering the influence of shear deformation on the moment of inertia, the classical Timoshenko beam theory was modified in this paper. Based on the method of reverberation ray matrix (MRRM), the bar with linearly varying circular cross-section was evenly divided into multiple constant section beams. The formulation was deduced for solving the natural vibration frequencies of the modified Timoshenko beam with variable cross-section under three classical boundaries (simply supported-simply supported, clamped-clamped, and clamped-free). The effects of the number of segments and the length of beam on the natural frequency of modified Timoshenko beam with variable cross-section were analyzed. The calculated results were then compared with those of the classical Timoshenko beam under the same boundary conditions. The results show that the MRRM has good accuracy and fast convergence. Under the same boundary conditions, the natural frequencies of modified Timoshenko beam are lower than those of classical Timoshenko beam, and the shorter the beam, the greater the influence of shear deformation on the moment of inertia.

Abstract:To study the numerical modeling method for mechanical behavior of stainless steel under cyclic loading, based on the OpenSees platform, the test results on specimens of austenitic stainless steel and duplex stainless steel under cyclic loading at home and abroad were simulated, and the quasi-static test results of precast segmental bridge pier with austenitic stainless steel were also simulated. All the simulation results were compared with the test results. It is found that the simulated stress-strain hysteresis curves of stainless steel under cyclic loading agree well with the test results, and the numerical model could predict the response of the austenitic and duplex stainless steels under different cyclic loading modes. The mechanical behavior of stainless steel under monotone loading is different with that under cyclic loading, so it should be modeled and valued separately. The simulation results of hysteretic behavior of the precast segmental bridge pier with austenitic stainless steel agree well with the test results, which further verifies the accuracy of the modeling method proposed in this paper.

Abstract:As a special kind of ground motion, the damage of long-period ground motion to structures has attracted the attention of scholars at home and abroad. Ten typical long-period ground motions from KiK-net and K-NET networks and ten short-period ground motions at home and abroad were selected in this paper, and their differences in time-history characteristics and response spectrum characteristics were compared and analyzed. The selected ground motions were input into a steel frame structure model, and through a nonlinear time-history analysis, the response differences of the steel frame structure under long- and short-period ground motions were studied. The results show that the average peak ground acceleration of short-period ground motions is 3.26 times that of long-period ground motions, and the average peak ground displacement is 10.89% lower than that of long-period ground motion. Under short-period ground motion, the average value of acceleration response at the top of the steel frame structure is 5.16 times that under long-period ground motion, and the average value of displacement response at the top of the structure is only 0.91% more than that under long-period ground motion. Under the action of long-period ground motion, the response of story drift ratio of the structure is larger, and the bottom of the structure is affected more widely. For high-rise steel frame structures in areas with long-period seismic hazards, long-period and short-period seismic hazards should be considered respectively. For medium- and long-period steel frame structures, it is suggested that the peak displacement should be selected as the seismic analysis index.

Abstract:In mountainous areas of southwest China, the geological conditions are complex and earthquakes occur frequently. In addition to landslides and debris flows, earthquakes can also lead to a large number of collapse and rockfall disasters, causing serious damage to infrastructure. Badai Village, which was located along the Chenghai fault zone with high risk of earthquake and typical distribution of dangerous rock mass, was taken as the research object in this paper. The influence area of dangerous rock mass under an assumed earthquake was analyzed, and the disaster risk of the expressway at the foot of mountain was evaluated. Based on unmanned aerial vehicle (UAV) images, the position and dimension parameters of the dangerous rock mass were quickly obtained by using the image recognition technique, and the recognition accuracy reached 76.2%. Then, the parameters of dangerous rock mass were substituted into the two-dimensional numerical simulation software Rocfall, and combined with the seismic energy calculation formula, the movement distance of dangerous rock mass under seismic action was calculated. The calculation results show that the nearest distance between the highway and the impact area is only 57 meters, so protective measures such as retaining walls should be built at the foot of slope.

Abstract:The occurrence of accumulation landslides in the edge of the Qinghai-Tibet Plateau is closely related to the effect of geological structures, heavy rainfall, and earthquakes, many of which are large-scale high-position accumulation landslides. To explore the mechanism and stabi-lity of large-scale high-position accumulation landslides, the Jiangdingya landslide in Zhouqu County was taken as the research object. The general situation and causes of the landslide were first analyzed from its geographical location and geological conditions. Then, the landslide calculation models were divided based on the traditional transfer coefficient method, and the variable slope method for landslide stability analysis was proposed. Finally, Midas GTS NX software was used to simulate and analyze the stability of Jiangdingya landslide under natural conditions, and the results were compared with the results of traditional and improved algorithms. The results show that: (1) Topographic slope, stratigraphic lithology, active faults, and historical strong earthquake in the study area are the internal causes of the landslide. The external causes are the mechanical strength reduction of rock and soil due to continuous heavy rainfall, the rise of Bai-long River water level and acceleration of flow velocity at the front edge of the landslide caused by rainstorm, the instability of the front edge, and the traction sliding at the middle and rear edges of the landslide. (2) When using the transfer coefficient method to calculate the landslide stability, the change of sliding surface inclination greater than 10° will lead to large errors in the result, so the improved variable slope method was proposed, and the numerical simulation were carried out on the Jiangdingya landslide to verify the effectiveness of the method. (3) The simulation results under natural conditions indicate that: the front edge of the landslide mainly shows horizontal slip and uplift, and the middle and rear parts of the landslide mainly show vertical subsidence. Therefore, large displacements occur in some areas of the landslide, indicating the possibility of local sliding. However, the displacement in other areas is small, and the landslide is in a stable state as a whole. The research results can be used as a reference for the stability analysis of large-scale high-position accumulation landslide.

Abstract:To study the seismic vulnerability of steel portal frame structures based on the finite element model validation, the time-frequency conversion of time-history response of a measured portal frame structure under environmental excitation was carried out according to the power spectrum method, and the structural eigenvalues were extracted as the objective function for the finite element model validation. The finite element model was updated through multiple iterations with the complex method. The incremental dynamic analysis was conducted on the validated model, and the seismic vulnerability curves of the structure were then obtained. Based on β distribution, the seismic damage index expression was constructed and the optimization ratio curve of seismic damage index was drawn, and then the seismic performance of the structure with viscous dampers was analyzed. The results show that the finite element model validation theory can reduce the error caused by the uncertainty of structural parameters, thus making the performance state of the finite element model close to the real structure. Compared with the initial structure, the structure with viscous dampers has better seismic performance, and the seismic capacity of the structure can be improved by about 30%.

Abstract:As the building industry in China gradually transforms and upgrades to intelligent construction, the number of sensors involved in the seismic response and health monitoring technology of high-rise structures, the amount of data to be processed, and the complexity of the system are increasing. In this paper, to meet the intelligent monitoring demand of seismic response and health of high-rise buildings, LoRa spread spectrum communication technology based on the Internet of Things was introduced, and the software and hardware platform scheme of high-rise buildings' seismic response and health monitoring based on LoRa was designed and implemented. The system consisted of multiple LoRa terminal nodes, LoRa gateway, OneNET server, and users. The monitoring data were transmitted through the LoRa network, and the LoRa gateway was connected to the cloud platform through the ESP8266 module to form a visual monitoring interface for the collected monitoring data. The test results show that the packet loss rate of the system within 3 km in an urban open environment is less than 8%. The system can realize the long-distance, low-power, and reliable wireless transmission of seismic response and health monitoring data of high-rise structures, and help users accumulate vibration response data under earthquake, evaluate the state of building structures and manage facilities.

Abstract:To obtain the disaster mode and prevention measures of loess seismic landslide, detailed landslide data and distribution characteristics were needed, so the recognition method using satellite images is the basis for cataloging the loess seismic landslides. By summarizing the spatial distribution characteristics, plane morphological characteristics, development characteristics, and associated hydrological characteristics of loess seismic landslides, seven kinds of identification marks for loess seismic landslides using satellite images were summarized in this paper. The spatial distribution regularity of loess landslides in Tongwei area were studied by the proposed method. The results show that the loess landslides obtained by the satellite image recognition method are similar to the field investigation results. The landslides in Tongwei area are characterized by gentle slope development, low angle, medium and long distance, large volume, and obvious direction.

Abstract:The construction and operation of urban transportation cannot avoid the influence of ground fissure activity due to the linear characteristics. The finite element model of a three-span continuous beam bridge orthogonally crossing ground fissure was established based on MIDAS GTS NX. The variation of displacement fields and stress fields of the continuous beam bridge’s box girder and pier under different settlement of ground fissure were analyzed. The results show that under different settlement conditions, the differential settlement areas of the box girder structure remain the same, and the width is basically the same as that of the influence zone of ground fissure:both the longth of hanging wall and foot-wall are 20 m, 40 m in total. The deformation of the box girder can be divided into three sections, that is, uplift area, differential settlement area, and overall settlement area. The surface of box girder at hanging wall is mainly subjected to compressive stress, while that at footwall is mainly subjected to tensile stress. The stress of box girder at the position of pier increases significantly, and the failure of box girder structure tends to occur at the footwall pier of ground fissure due to the sudden increase of tensile stress. The differential displacements of bridge piers on both sides of the mid-span within the influence range of ground fissure significantly change, while the piers outside the influence range of ground fissure are less affected. The research results can provide an important reference for the research on the disaster-causing mechanism and disaster prevention of the existing and planned continuous beam bridges.

Abstract:Based on the incremental dynamic analysis (IDA) curve, this paper evaluated the seismic performance of high pier columns of a novel railway bridge with replaceable members under 9-degree design, rare, and huge earthquakes. A finite element analysis model of the whole bridge was established. Strain of the most unfavorable section of the pier column was chosen as the damage index, and the ground peak acceleration was chosen as the seismic intensity measure. Under the input of 357 seismic waves, the IDA curve cluster and 50%, 84%, and 16% curves of the key sections of pier column were obtained through the IDA analysis. Combined with the defined limit state, the number and location of possible plastic hinges on the pier column were discussed, and the seismic performance of pier column was evaluated by drawing vulnerability curve. The results show that the replaceable members yield first in the pier, from PGA=0.5g to PGA=1.1g, and the replaceable members realize graded energy consumption. The probability of pier column in nearly intact state under the action of 9-degree rare earthquake is about 99.5%. For the novel high pier structure with replaceable members proposed in this paper, the probability of exceeding the nearly intact state under 9-degree earthquake is 36.6%, and the probability of exceeding the repairable damage state is less than 1%. The high pier structure with replaceable members has excellent seismic performance and has a good application prospect in near fault areas.

Abstract:The earthquake damage assessment of buildings is of great significance to the assessment of earthquake loss in urban areas and the rapid relief after earthquake. In this paper, the seismic damage assessment of regional buildings considering the interaction between structures was carried out. The existing simplified discrete model based on the analysis of structure-soil-structure dynamic interaction (SSSI) was first adopted. On this basis, the influence of foundation rotation on the output response was deducted, and the nonlinear multi-degree of freedom model of superstructure was introduced. Then, the simplified nonlinear multi-degree of freedom discrete model considering SSSI was obtained, and the seismic damage assessment method of regional buildings considering SSSI was established. Finally, the seismic damage assessment of buildings in Wangjiang Campus of Sichuan University during the Wenchuan earthquake was carried out by using the proposed method. The seismic damage of buildings in Wangjiang Campus without considering SSSI was also calculated by using the HAZUS. The actual seismic damage survey data, the HAZUS calculation results, and the calculation results of the proposed method in this paper were compared and analyzed. The results indicated that compared with the HAZUS results, the seismic damage calculation results of the proposed method are closer to the actual survey data; compared with the seismic damage calculation results of buildings without considering SSSI, the accuracy of those considering SSSI is higher and can better reflect the actual earthquake damage of buildings.

Abstract:Taking the pile foundation of a bridge in Haining section of the second passage of Beijing-Hangzhou Canal as the research, the scientific and technical problems of the construction and safety protection of important bridge projects crossing dense intersections during the excavation of overland waterway were studied. Through on-site investigation and indoor tests, the channel excavation in deep soft soil of the study area was simulated and calculated by using the 3D numerical simulation technology. The horizontal offset of adjacent bridge pile foundation during the channel excavation was analyzed, and the influence of different pile length and pile diameter on the horizontal offset of bridge pile foundation caused by adjacent channel excavation was mainly explored. The results show that the excavation of waterway will inevitably cause soil disturbance and displacement of pile foundation. For super-long piles, the increase in the pile diameter is of limited help in improving the horizontal bearing capacity and controlling the horizontal inclination of pile foundation. The pile length of bridge pile foundation in soft soil area should be greater than the critical value, otherwise, the horizontal bearing capacity of the pile foundation is not enough to offset the influence of soil excavation on the pile, which will lead to a sharp increase in the horizontal inclination of the pile and cause damage. The research results can provide reference for similar projects and construction in the future.

Abstract:The loess in the Lishan piedmont fault zone in Lintong District of Xi'an City was studied with fiber-reinforced treatment. The dynamic triaxial tests of reinforced loess were carried out based on the orthogonal test plan. The difference of dynamic elastic modulus of fiber reinforced loess was discussed, and the influencing factors were compared and analyzed. Through the range analysis of the orthogonal test results, it is concluded that the fiber length, fiber content, and soil saturation are the three major factors affecting the dynamic elastic modulus of fiber reinforced loess, with an order of soil saturation, fiber length, and fiber content. The results of variance analysis show that the significant levels of soil saturation on glass fiber reinforced loess and polypropylene fiber reinforced loess are 0.035 and 0.058, respectively, indicating that the soil saturation has a prominent effect on the dynamic elastic modulus of fiber reinforced loess. The optimal levels are 0.6% fiber content, 50% soil saturation, and 12-mm fiber length for both the glass fiber reinforced soil and polypropylene reinforced soil. The results also show that the dynamic elastic modulus of the two reinforced loess is about 1.5 times that of fiber-free conditions. There is a positive correlation between the fiber length and the dynamic elastic modulus of reinforced loess. Both the dynamic elastic modulus of glass fiber reinforced loess and polypropylene fiber reinforced loess increase first and then decrease with the increase in fiber content. The fiber reinforced treatment of loess is helpful to improve the strength of loess and ensure the safe construction and operation of engineering foundation in the fault zone.

Abstract:Cangdong fault, the largest normal fault in the west of the Bohai Bay basin, is also the boundary fault between Cangxian uplift and Huanghua depression. In this paper, the Quaternary activity and deep structural features of the Cangdong fault were studied in depth by using the seismic exploration data from five shallow survey lines obtained in the past 30 years and the borehole data near the lines. Based on the shallow seismic exploration results, it was found that the buried depth of Cangdong fault up-breakpoint changes from deep to shallow from south to north, but it is concentrated in the range of 118-300 m. It is inferred that the latest activities occurred at the middle Pleistocene, and the active age of the fault is not characterized by segmentation. Based on the data of deep seismic reflection, magnetotelluric sounding, distribution of small earthquakes, and focal mechanisms of moderate-strong earthquakes in the Cangzhou area, the deep structural features of the fault were further analyzed. It was found that the Cangdong fault is characterized by a typical listric normal fault, which turns into nearly horizontal extension at a depth of about 10 km. Cangdong fault is not the main earthquake-controlling fault in the study region, or it is only a low-risk active fault, so its risk of medium-strong earthquakes in the future may be relatively low.

Abstract:Based on three items of GPS deformation data (2009-2011, 2011-2013, and 2013-2015), the dynamic evolution results of strain field in the eastern section of Northern Tianshan Mountains were calculated using the least square collocation method and the partial derivative relationship between displacement and strain. The current activity characteristics of tectonic area in the eastern section of Northern Tianshan Mountains were re-recognized, and the internal relationship between the spatial distribution characteristics of the strain field and the Hutubi MS6.2 earthquake in 2016 was discussed. The results show that: (1) The temporal change of crustal movement rate and the strength of strain field in the study area show the characteristics of "weak-strong-weak". The principal compressive strain in the N-S direction in the first and third periods is small, about (1~2)×10^-8/a, and that in the second period is significantly enhanced, about (1~6)×10^-8/a. The slip rates in the three periods show that the section of Northern Tianshan Mountains is characterized by dextral strike-slip of "strong [(2.2±0.4) mm/a]-weak (not obvious)-strong [(3.0±1.0) mm/a]", respectively; (2) Earthquakes may be more likely to occur in the center of the four quadrants of the surface strain field' isoline or in the high-density gradient zone of the positive and negative transition zone, which may be the deformation precursor observed by GPS data in the seismogenic process of earthquake; (3) Strong earthquakes are more likely to occur in the high-value area or edge area of shear strain rate (maximum shear strain rate); (4) Compared with the plane strain rate and the maximum shear strain rate, the change of principal strain rate is more suitable for explaining the direction and properties of block movement.

Abstract:The network system of seismic mobile field observation has the characteristics of no public network, strong mobility, wide range, high density, and complex environment. To realize the low-cost, efficient transmission, and rapid deployment of array networking in seismic field monitoring, the LoRa network was taken as the main communication network in this paper. Combined with the wireless network technology of Wifi and ZigBee, a portable wireless compo-site communication gateway with low power and fast networking was designed and implemented. The experimental test results show that the gateway can achieve the highest air transmission rate of 21 kbps within 2 km under Lora network, and it is suitable for efficient transmission and rapid deployment of seismic field monitoring.

Abstract:In this paper, based on the earthquakes occurred in the Longmenshan region from 2011 to 2020, the cumulative Benioff strain in three sections were estimated. The results show that there is a step-up in the northern section of Longmenshan fault to the Jiuzhaigou M_S7.0 earthquake, and the cumulative Benioff strain uplift within one year after the earthquake is about 2 000×10⁸; there is a significant step-up in the middle section of Longmenshan fault to the Lushan M_S7.0 earthquake, and the cumulative Benioff strain uplift within one year after the earthquake is about 5 300×10⁸. Therefore, it is believed that the correlation between the middle section of Longmenshan fault and the Lushan earthquake is high, followed by that between the north section of Longmenshan fault and the Jiuzhaigou earthquake. As a description of the correlation between regional tectonic movement and corresponding earthquake, the uplift amount is of refe-rence significance to study the dynamic source, seismogenic structure, and seismogenic mechanism of earthquake. The research results also show that the time-varying slope of cumulative Benioff strain decreases prior to the earthquake, which may be the manifestation of the stress relaxation process before earthquake. This paper is just a preliminary study on the Benioff strain, and more earthquake cases are needed to study its mechanism and whether it can become a preparation index for large earthquakes.

Abstract:Weiningbeishan, Ningxia, is located at the convergence zone among three active blocks, i.e., the Tibetan Plateau, the Alax Block, and the Ordos Block. Detection of the active faults in this area is of great significance for clarifying the boundary of active blocks and planning the layout of Zhongwei Industrial Park. By means of shallow seismic exploration, drilling joint profile exploration, and trenching, this paper carried out a comprehensive exploration on the inferred fault at the southern margin of Weiningbeishan, found out the fault distribution and the characteristics of stratum dislocation, and preliminarily identified the activity of the proved fault. The results show that the normal southern margin fault of Weiningbeishan under the geomorphic scarp inferred by former researchers is not found, and a thrust fault is developed in the bedrock to the north of the geomorphic scarp. The shallow seismic exploration profile reveals that the buried depth of upper breakpoint of the fault is 35-40 m. The drilling joint profile surveying and tren-ching found that the fault offset the Carboniferous and Oligocene strata, however, the overlying Late Pleistocene sediments are not faulted, indicating the fault is not active. In addition, the shallow seismic profile reveals that a NWW-trending buried normal faultis developed in the Zhongwei basin, and the buried depth of upper breakpoint is 60 m. Combined with the stratigraphic age of the basin, we infer that the fault has not been active since the Late Pleistocene.

Abstract:To systematically summarize the characteristics of surface ground and underground seismic observation, the ground GL-S60 and underground GL-S60B broadband seismometers in the same site of Liyang seismic station were comparatively analyzed in this paper. The results show: (1) The azimuth angle of underground seismometer is about 176.5°: the southeast and northwest directions are roughly reversed. (2) The vertical correlation coefficient is better than horizontal correlation coefficient. Due to disturbance of human activities, correlation coefficient in daytime is lower than that at night. (3) Due to the disturbance of NS-direction highway near the station, the ground base noise in the horizontal direction is higher than that in the vertical direction, and that in the NS direction is the largest. The base noise of underground seismometer is small as a whole, and the noise in the horizontal direction is less than that in the vertical direction, indicating that deep-well observation can effectively reduce the base noise, especially in the horizontal direction. (4) The signal-to-noise ratio recorded by the underground seismometer is inferior to that recorded by the ground seismometer, for the observation on the ground has a certain amplification effect on the seismic wave. Underground observation can effectively reduce the noise level, but it does not mean the output of high signal-to-noise ratio data, which needs to be comprehensively analyzed in combination with the actual observation data.

Abstract:This paper analyzed the data of constant chemical components,hydrogen and oxygen isotopes,and tritium activity of Jiujiang No.2 well water,atmospheric precipitation,Maweishui spring water,and Tianhuajing reservoir water in Jiangxi Province,discussed the hydrochemical type,genesis,and recharge cycle process of groundwater in Jiujiang station,and then revealed the geochemical characteristics of Jiujiang No.2 well with sensitive response to tectonic activity.It was found that the hydrochemical type of Jiujiang No.2 well is HCO₃-Ca·Mg type;the δ¹⁸O indicated that the water of Jiujiang No.2 well belongs to the genetic type of atmospheric precipitation,and the recharge elevation is 647 m;the groundwater age given by tritium activity analysis showed that Jiujiang No.2 well has both old water supply and new water supply of nearly 10 years.The analysis results showed that Jiujiang No.2 well has both the characteristics of shallow surface water and deep circulating water,suggesting that the aquifers of two different recharge sources rise to the shallow surface through different circulation paths,and the deep aquifers may carry some radon from deep tectonic activities,such as the significant anomalies before the Ruichang-Yangxin M_S4.6 earthquake.

Abstract:On May 27, 2014, an M4.0 earthquake occurred in Fangxian County, Hubei Province, and the water level of the well in Sanhai Village of Fangxian County showed obvious precursory anomaly. The study well is the only static well with water temperature negative gradient in Hubei Province. Previous research on the dynamic change of the well water temperature mainly focus on the comparative study of water temperature and water level, as well as hydrochemical analysis, and few studies focus on the combination of water temperature and geological structure. Combined with InSAR image map, hydrochemical data, hydrogeological data, and geological structure data, the causes of water temperature negative gradient of the well was discussed in this paper, as well as whether the water temperature and water level of the well were affected by surrounding geological structures. The research results can offer a certain reference for the correlation analysis between underground fluid and surrounding structures.

Abstract:This paper analyzed the characteristics of ambient noise on the east side of Xar Moron fault zone according to three key values: root mean square (RMS) of velocity at 1-20 Hz, power spectral density (PSD) of acceleration, and corresponding probability density function (PDF). The continuous data were recorded by 26 mobile seismic stations in the study area set up under the project "ChinArray-eastern North China". The results indicate that the temporal and spatial distributions of ambient noise in the study area show various characteristics at three different frequency bands: (1) The temporal and spatial distribution of ambient noise in the high frequency band is significantly different, and the noise source mainly comes from human activities. (2) The ambient noise in micro-seismic frequency band mainly comes from marine activities. The temporal and spatial distribution of ambient noise at high-frequency micro-seismic frequency band has no difference, while that at low-frequency micro-seismic frequency band has certain difference, which is due to the temperature change and micro deformation of observation wells; the difference is more prominent in the daytime than at night. (3) In the low frequency band, the three-component noise in the daytime is larger than that at night, and the level and dynamic range of noise in the horizontal direction are higher than that in the vertical direction, for the influence of ambient temperature change and ground tilt in the daytime is greater than that at night, and the horizontal direction is more sensitive to temperature and ground tilt than the vertical direction.

Abstract:Taking the underground geo-electrical resistivity observation device at Pingliang station as an example, this paper analyzed the relationship between the layout of geo-electrical resistivity observation device and the interference of metal pipelines by using the finite element numerical simulation method. The results show that: (1) The influence of metal pipeline perpendicular to the survey line on geo-electrical resistivity observation is significantly less than that parallel to the survey line. The most effective suppression method is to increase the avoidance distance of metal pipeline. (2) When the metal pipeline is set in the center of electrodes, the increase of the buried depth of electrode may not effectively suppress the interference. The effect is significant when the metal pipeline is perpendicular to the survey line direction, but it is not ideal when it is parallel to the survey line direction. (3) The influence of metal pipeline on the underground geo-electrical resistivity observation is relatively complex, which is related to many factors, i.e., the device system (observation polar distance, electrode buried depth), the layered medium electrical structure, and the properties of metal pipeline (conductivity, cross-sectional area, length, distance), etc. The method proposed in this paper can quickly determine the abnormal changes of data, thus having a certain reference significance for anomaly tracking. It can also provide a theoretical basis for the new underground geo-electrical resistivity observation device, so as to improve the observation efficiency of station.

Abstract:Based on 20 395 items of P-wave initial motion data of 3 036 earthquakes from 2008 to 2018, the stress field at the junction of Shanxi, Shaanxi, and Henan Provinces was inverted and calculated by using the composite focal mechanism method, and the distribution of fine stress field in the shallow part of the study area (0.15°×0.15°) was obtained. The results showed that: (1) Most areas at the junction of Shanxi, Shaanxi, and Henan Provinces are mainly under the strike-slip and extensional stress regime. The orientation of the principal compressive stress axis is NE-NEE, and the orientation of the extension stress axis is nearly NS, indicating that the Shanxi rift basin is a product of typical strike slip and extension; (2) The characteristics of compressive stress field around Huashan piedmont fault and Luoyang basin reflect that the thrust mechanism is the main component in these two areas; (3) The maximum P-wave contradiction ratio appears in the area between Fengmenkou-Wuzhiling fault zone and Xin'an-Jiaxian fault zone, indicating that this area with complex stress field is controlled by the dual effect of extension and strike slip; (4) There are obvious heterogeneity characteristics in the stress field at the junction of Shanxi, Shaanxi and Henan, which is mainly reflected in the transition area between uplift and depression.

Abstract:With the development of earthquake engineering in China, the application scope of intensity has gradually changed. From the collected seismic damage data over more than half a century, it is found that in low-intensity regions, the proportion of similar building structures in basically intact state increased, and the proportions of other damage states decreased; while in high-intensity regions, the proportion of similar building structures in complete damage state increased. From the seismic damage data of Wenchuan earthquake, Lushan earthquake, and Ludian earthquake in recent years, it is found that in the same intensity area, the damages of fortified structures, unfortified structures, and structures with different fortification intensities are quite different. If the intensity represents the earthquake consequences, the intensity evaluated by the average level of earthquake damages should be different, thus implying that the meaning of intensity is the seismic action reflected by earthquake damage. Therefore, when we determine the intensity according to different types and different fortification levels of structures, a relatively unified standard is needed. Since the abundant damage data in China are from unfortified structures, it is suggested to establish the adjustment coefficients of average damage index/damage ratio corresponding to unfortified structures based on the statistical relationship between the average seismic damage index and (or) damage ratio of different fortification standards, various structures, and seismic damage levels of structures under a certain intensity and the average seismic damage index and (or) damage ratio of similar structures without fortification. The intensity could be determined by the damages of fortified structures.

Abstract:To deeply analyze the influence of the 2021 Yangbi M_S6.4 earthquake on the surrounding faults and the effect of static Coulomb stress between earthquake sequences, based on the rupture model of the mainshock and the analytical formula proposed by Okada, this paper calculated the static Coulomb failure stress (CFS) generated by the mainshock on the surrounding faults. The result shows that the magnitude of CFS in the middle part of the Weixi-Qiaohou fracture zone, the northern segment of the Lancang River fracture zone, the northern segment of the Red River fracture zone, and the middle segment of the Nujiang River fracture zone are increased by several kPa. Then, the horizontal stress field and the displacement field in surrounding area generated by the earthquake were calculated. It is found that the materials on the east and west sides of the epicenter flow outward, and those in north and south sides converge to the epicenter, with subsidence in north and south sides and uplift in east and west sides. The stress field generated by the earthquake shows EW-trending compression and NS-trending extension, which counteracts the background tectonic stress field to a certain extent. Finally, the triggering effect between the foreshock-mainshock-aftershock sequence was investigated. The results show that the static Coulomb stress produced by the foreshock promotes the occurrence of the main shock. Near the depths of 2 km, 13 km, and 18.5 km, high proportion of triggered aftershocks (with positive Coulomb stress changes generated by the foreshocks and mainshocks) is founded, but at the depth of 7 km (with maximum slip in co-seismic fault model), most of the aftershocks are distributed in the negative Coulomb stress region (stress shadow zone). These focal mechanisms are quite different with that of the main shock. Therefore, the maximum static CFS was calculated by simulating the fault planes with the maximum shear stress as the receiving fault planes of the aftershocks. The result shows that the aftershocks in stress shadow zone still have the possibility of being triggered.

Abstract:The spatial distribution and activity characteristics of Shimian fault, an important part of the Daliangshan fault zone, have great theoretical significance for the study of regional tectonic stability, and also have important application value for urban construction and risk assessment in this area. Combined with the data of geological survey, previous trenches, and shallow artificial earthquakes, a comprehensive analysis was made through the geochemical exploration of fault gas radon along the Shimian buried fault, and the results show that: (1) The spatial location of the fault revealed by fault gas radon detection is in good agreement with that interpreted by geophysical exploration and trenches. The fault is located near the peak concentration and is distributed in the abnormal range of the main peak. (2) The tendency of Shimian buried fault determined by fault gas radon detection is consistent with the results revealed by geophysical exploration and trenches. According to the comprehensive data analysis, the occurrence of the fault is N38°-45°W/SW∠70°-80°. (3) The relative activity of different segments of Shimian fault was judged by using the contrast value of fault gas Rn concentration. It is found that the activity of the southern segment of the fault (Nanya River basin) is stronger than that of the northern segment (Dadu River basin).

Abstract:The vegetation index and the light index used to quantitatively evaluate the post-disaster recovery situation have important scientific significance for the evaluation of economic construction and ecological recovery in the disaster area. An M_S6.0 earthquake eccurred in Changning County, Yibin City, Sichuan Province on June 17, 2019. Four kinds of light indexes and the enhanced vegetation index (EVI) in the earthquake-striken area were obtained based on the monthly NPP-VIIRS data, MODIS-EVI data, and statistical yearbook data. The nonli-near regression prediction models of NPP-VIIRS data and MODIS-EVI data were established to predict the light index and vegetation index, respectively. Through a comparative analysis of the predicted and actual data, the recovery situation after the earthquake was evaluated. The results show that both the total night-time light (TNL) and the EVI decrease significantly after the earthquake, and the values decrease more obvious with closer to the epicenter. The decline of EVI data is lagging and persistent, and the restoration of night lighting is better than that of vegetation. The impact of earthquake on TNL is higher than that of EVI, and the impact decreases with the increase of epicentral distance. This paper carries out research from two aspects of economy and environment, thus having a certain application value for earthquake rescue and post-earthquake recovery evaluation.