Abstract:A type of assembled joints for timber column-reinforced concrete hybrid structures was designed to study the nonlinear mechanical properties of beam-to-column flexible joints for assembled timber column-reinforced concrete hybrid structures. A finite element model was established by using the ABAQUS finite element software, and the analyses under monotone loading and low-cycle repeated loading were conducted for the model. Effects of rubber hardness and vertical load on the nonlinear mechanical properties of assembled joints, including the damage characteristics, hysteresis curve, skeleton curve, bearing capacity, and energy dissipation capacity,were mainly studied. Compared with related literature, the feasibility of the proposed method was verified. Results show that the main failure modes of the flexible joint are compression buckling and tension lifting of the column base and compression deformation of rubber. The bearing capacity, stiffness, and ductility of the flexible assembled joint are proportional to the hardness of filled damping materials. The lateral tilting of columns and the lifting of column bases are effectively limited by the increase in the hardness damping materials. When rubber materials with 71 HA hardness are used, their energy dissipation capacity is good. Meanwhile, the vertical load has a considerable influence on the damping ratio of the assembled joint, which effectively improves the viscous damping ratio of the assembled joint by increasing the vertical load.

Abstract:A quasi-static test study of one near-surface mounted (NSM) strengthening joint with carbon fiber-reinforced polymer (CFRP) laminate, and one comparative joint was conducted in this study to evaluate the seismic performance of cruciform RC beam-column joints strengthened with NSM CFRP laminates. Test results show that the use of NSM CFRP laminates in joints and adjacent beam ends could change the failure mode from the joint shear to the beam flexural failure and further relocate away the plastic hinge from the column face. Moreover, the capacity and ductility of joints were increased by 16.3 %and 13.7 %, respectively. Finite element models were also established using ABAQUS and then used to perform parametric studies to understand the effects of several critical design factors on the seismic behavior of joints. Results show that the bearing capacity of joints increases with the laminate area and concrete strength and decreases with the increase in the laminate spacing. The proposed strengthening method, which reflects the seismic design concept of plastic hinge transfer, improves the shear strength of the joint core area and the bending strength of beam ends. Thus, this method is available for the seismic strengthening of RC joints.

Abstract:In traditional seismic analysis studies, transmission towers are usually assumed to be fixed on the ground, neglecting the soil-structure interaction (SSI) that may lead to inaccurate seismic performance evaluation of transmission towers. A comprehensive analysis of the seismic response, collapse damage, and collapse vulnerability of an actual 1000- kV transmission tower was carried out, considering SSI under seismic excitations. In ABAQUS, the interaction between soil and pile was simulated by setting zero-length springs along piles. A finite-element model of the transmission tower considering SSI was also established. Based on the numerical model, the dynamic characteristics and structural dynamic response of the transmission tower were analyzed. The impact of SSI on the collapse mechanism and vulnerability of the transmission tower was studied using the incremental dynamic analysis method. Results show that the vibration modes of the transmission tower with and without considering SSI are similar, but the natural frequencies differ greatly. Ignoring SSI will lead to underestimating the seismic response of the transmission tower and overestimating its collapse resistance. Therefore, studies considering SSI can improve the seismic capacity of the transmission tower, thereby ensuring the safety of the transmission line.

Abstract:A bidirectional laminated shear continuum modeled soil box was developed, and a finite element analysis model of pipe-soil interaction was established to study the dynamic response of buried pipelines under seismic excitation. The seismic response of buried pipelines under transverse non-uniform seismic excitation was analyzed by numerical simulation, and the simulated results were compared with the test results. Results show that the peak strain of pipelines in the simulated and test results is large in the middle and small at two ends; the peak strain in the middle is at least 1.6 times that at two ends. The peak values of pipeline and soil acceleration increase with the loading level, the multipeak frequency gradually diffuses from the frequency domain of 0-10 Hz to 10-20 Hz, and the pipeline moves freely. The displacement of soil increases with the loading level; the slope of the displacement curve decreases when the loading level increases to 0.4 g, and the nonlinear behavior of soil is observed. The conclusions show the rationality of numerical simulation analysis and the reliability of test results, thus providing a basis for studying the effects of transverse non-uniform excitation on the seismic response of buried pipelines.

Abstract:A centrifugal shaking table test on a dry sand site was designed and conducted to study the influence of different seismic waves on the peak value of soil acceleration during its upward transmission, and the variation law of acceleration amplification factor along the depth was obtained by comparison. Results show that the amplification factor of ground motion acceleration along the depth decreases with the increase in amplitude. Moreover, a certain attenuation rate of the amplification factor is observed when the amplitude of the wave increases, and the attenuation rate decreases with the increase in the amplitude. Under the action of seismic waves with the same amplitude and different frequency spectra, the acceleration amplification factor of the invariable amplitude sine wave is the largest, followed by the LEAP wave, and that of the El-Centro wave is the smallest. The analysis of the soil acceleration amplification factor and its attenuation rate is helpful in studying the dynamic response of similar sites, which also has a certain reference value for seismic design.

Abstract:An innovative fabricated double steel tube-encased and high strength concrete-filled (FDSHC) composite shear wall suitable for high-rise buildings is proposed in this study, and its seismic performance is verified by experiments. The failure mode and hysteretic behavior of specimens were analyzed through the compression-bending-shear test of six FDSHC specimens with two stories and the tension-bending-shear test of six FDSHC specimens with a single story. The effects of axial force, section content ratio of concrete-filled steel tube, eccentricity, and the pos-sibility of welded outer steel tube on their seismic performance were studied. Results show that the failure mode of the specimens is a bending-shear composite failure. The specimens have high bearing capacity under the compression (tension)-bending-shear composite loads, demonstrating full hysteretic loops, good energy consumption capacity, and overall assembly performance. A high axial compression ratio (or small axial tension ratio) leads to high peak strength. Meanwhile, a large eccentricity results in a weak energy consumption capacity. The influence of section content ratio and the possibility of welded outer steel tube was not observed. Compared with the traditional prefabricated concrete shear wall, FDSHC composite shear wall has the advantages of easy assembly, high bearing capacity, and low cost. The seismic performance of this composite shear wall is also excellent, which is expected to be popularized and applied in prefabricated high-rise buildings.

Abstract:The base isolation technique is widely applied in building structures to mitigate structural seismic responses, while the acceleration response of the main structure is reduced at the cost of isolator deformation in the isolation system. A hybrid isolation system comprising a tuned inerter damper (TID) and an isolator can remarkably reduce the displacement response of the isolation layer. Similar to a traditional tuned mass damper (TMD), a TID comprises an inerter, tuning springs, and damping elements. Therefore, the design formula of the TMD system can be directly used to determine the optimal parameters of TID. First, two design formulas of TID and TMD were derived and analyzed on the basis of motion equations of the single-degree-of-freedom system with additional TID. Then, the precondition and applicability of the two formulas were comprehensively discussed. Finally, the feasibility and effectiveness of the designed TID were val-idated by the benchmark model of the base isolation system. Numerical simulation results illustrate that the designed TID can significantly reduce the displacement and base shear responses of the base isolation structure without increasing the absolute acceleration response of the main structure.

Abstract:Earthquake is one of the main factors that induce slope instability. As a widely used geotechnical retaining structure, the seismic stability of gravity retaining walls remains a popular topic in geotechnical engineering. A semi-analytical horizontal slice method is proposed on the basis of the upper bound limit theory and the pseudodynamic approach to evaluate the active earth pressure of unsaturated filling soil under seismic action effectively. The work rates of unsaturated soil gravity and seismic inertia force with evident nonlinear distribution characteristics were computed to formulate the energy balance equation. The semi-analytical solution of active earth pressure was formulated explicitly according to the equation and then compared with the analytical solution to validate the proposed method. Parametric analyses of the impacts of soil suction and seismic excitations on the earth pressure estimations were also conducted. The findings demonstrate the following: (1) the active earth pressure is overestimated when soil suction is disregarded in the analyses. The suction effect relates not only to the type of filling soil but also to the characteristics of ground motion. (2) The active earth pressure depends significantly on the horizontal and vertical ground motions. The peak earth pressure slightly increases with the soil shear modulus and moves toward the negative direction; as the seismic period increases, the peak earth pressure slightly rises and moves toward the positive direction. (3) The impact of surcharge load on the earth pressure becomes increasingly evident in filling soil with large inclination angles. For filling soil with an inclination angle larger than 100^°, the earth pressure becomes markedly pronounced with large soil-wall friction angles.

Abstract:Self-centering (SC) wall structures show larger deformation capacity and almost no residual displacement than the traditional structure under earthquake excitation. However, energy dissipaters must be installed to increase the energy dissipation capacity for SC wall structures. Metal dampers are widely used in SC wall structures, which can significantly reduce the seismic response of structures under large earthquakes. However, these dampers have limited effect under small earthquakes. This paper applies the viscoelastic damper, which can dissipate energy under small deformation to SC wall structures. A 10-story SC wall structure was designed with viscoelastic and U-shaped metal dampers as additional energy dissipation components. The comparison between seismic performances of the structure using two energy dissipation mechanisms was conducted through elastic-plastic time-history analysis. Results show that the viscoelastic damper can significantly reduce displacement and acceleration responses under minor earthquakes. However, the energy dissipation capacity of the U-shaped metal damper will surpass that of the viscoelastic damper under large earthquakes. Therefore, the characteristics of different dampers should be considered in the design to further optimize the seismic performance of SC wall structures under earthquakes with different intensities.

Abstract:Ultrahigh voltage (UHV) transformer bushings have high seismic vulnerability. A realtime damage detection method is proposed on the basis of acceleration response signals of the bushing in this study to investigate damage detection for bushings when structural damage occurs under earthquakes. High-pass filtering and ensemble empirical mode decomposition were used to extract abnormal high-frequency components of signals as damage characteristics, and the highfrequency energy ratio was defined for the damage localization. A numerical case was conducted to simulate seismic responses of the structure under different damage scenarios, and the accuracy of the proposed method was verified. Research results show that the sudden damage to the structure during the earthquake will produce instantaneous high-frequency components in the acceleration response signal. The energy of instantaneous high-frequency components in the signal is related to the distance from the sampling point to the damage location. The energy will increase when the sampling point is close to the damaged location. Additionally, the data input of the proposed method includes acceleration responses of the structure for damage identification and localization, which are simple data types.

Abstract:The 17th World Conference on Earthquake Engineering (17 WCEE) was held in Sendai,Japan,from September 27 to October 2,2021.Owing to the impact of the COVID-19 pandemic,the conference was hybrid,combining online and offline attendees.The authors participated in the conference online.This study shares the latest achievements and development trends in geotechnical earthquake engineering and related fields discussed at the conference. Recent progress in geotechnical earthquake engineering was reviewed by analyzing relevant conference presentations and papers reviewing various topics, including sand liquefaction disasters, slope failure under earthquake, soil-structure interaction, ground failure and seismic safety of sites, ground motion.

Abstract:To improve the seismic performance of beam-column joints of assembled steel structures,nano-metakaolin/fluororubber (NMK/FKM) composites with high damping performance were first prepared in this study by melt blending method,and then dynamic and static mechanical properties of the new material were tested at four frequencies.Taking NMK/FKM nanocom-posites as the core energy dissipation material, a simulation analysis of the right-angle viscoelastic damper proposed in this paper was performed using finite element software ABAQUS. Results show that when the frequency is 1.5 Hz, the wide damping temperature range and TA value of NMK/FKM nanocomposites reach the peak, demonstrating the best damping performance of materials. The stiffness of the right-angle viscoelastic damper increases with the displacement amplitude. The hysteretic performance of the right-angle viscoelastic damper shows nonlinear characteristics under frequencies of 0.5,1.0, and 1.5 Hz; when the frequency rises to 2.0 Hz, the hysteresis performance shows linear characteristics. The hysteresis loop area, damper stiffness, and maximum damping force gradually decrease as the thickness of viscoelastic material layers increases. The energy dissipation performance of the damper is improved as the height-span ratio increases. The dynamic response of the right-angle damper is further enhanced by adjusting the height-span ratio of dampers and the thickness of damping materials.

Abstract:The alluvial filling soil on the side of bridge piers and its physical,mechanical,and geometric pa-rameters have important effects on train vibration propagation. Taking a pier and its adjacent alluvial filling soil and foundation site along the Tieling-Siping section of the Harbin-Dalian high-speed railway as the research object in this study, a finite element model was established, and the "effective value of vibration change" was defined. Combined with the theory of gray relational degree, the field measurement and numerical simulation method were used to reveal the influence of the alluvial filling soil and its parameters on vibration propagation. The following conclusions are obtained through the analysis. (1) Vibration characteristics of the supporting pad stone at the top of the pier are different from those of alluvial filling soil and the foundation site, which have amplification effects on the train vibration. (2) The vibration acceleration level of the alluvial filling side is larger than that of the unfilled side, and a rebound phenomenon will be observed at the boundary position of the alluvial filling soil. (3) The vibration acceleration level increases with the elastic modulus of alluvial filling soil, and its density and Poisson's ratio hardly affect the vibration propagation. Within 1 m from the pier, the vibration acceleration level increases with the damping ratio; when the distance is larger than 1 m, this level decreases with the increase in the damping ratio. (4) The vibration acceleration level increases with the length of the alluvial filling soil, and its height demonstrates an optimum value, which minimizes the vibration acceleration level on the side of the alluvial filling soil. Meanwhile, the sensitivity of each parameter of alluvial filling soil on the pier side to the ground vibration is in this order: elastic modulus ＞ length ＞ damping ratio ＞ height ＞ density ＞ Poisson's ratio.

Abstract:The consolidated undrained triaxial shear and scanning electron microscope tests were conducted on five layers of undisturbed peat soil with different buried depths from lacustrine sediments of Dianchi Lake，and the shear characteristics and microstructural changes of peat soil under different confining pressures were analyzed. Test results show that under the confining pressure of 50-1800 kPa，the common tangent of the limit stress of peaty soil shall be drawn in sec-tions rather than in a straight line. The effective stress path curve of peat soil changes from disordered to ordered with the increase in confining pressure. When the consolidation pressure is larger than 300 kPa, the effective stress path curve is in the shape of " 7 ," and the consolidated drainage flow increases linearly under the confining pressure of 50-300 kPa. The mechanism of the consolidation shear process was analyzed in accordance with the microstructural change and macro shear process. Under the action of confining pressure, soil particles produce displacement and the contact mode of particles changes from edge-surface to surface-surface. Large pores in the soil are squeezed into small pores, especially those with a diameter of 1 μm. The essence of soil deformation lies in the change in soil particle position. With the increase in confining pressure, the orientation of pores is improved, and the distribution of soil particles is uniform. The shear strength and related parameters of peat soil increase when its density changes from loose to relatively dense and finally to dense.

Abstract:On the basis of indoor triaxial shear test,the effects of initial moisture content and compactness on the shear strength index,stress path,and failure strength of the remolded loess from an airport site in Linxia,Gansu Province were studied.Pore characteristics of the remolded loess under different compaction degree were quantitatively analyzed by using microstructural im-ages from the indoor scanning electron microscope test. The relationship between pore characteristics and the failure strength was also established. The results show the following: (1) The stress-strain curves of remodeled loess under different initial water content and compaction degree are divided into three forms: softening type (below 7 %water content and above 90 %compaction degree), weak hardening type (below 7 %water content and 85 %compaction degree or above 9 %water content and 90 %compaction degree), and hardening type (other condition); (2) The stress path curve of the compacted loess takes the form of oblique straight line, which is not affected by the compaction degree and moisture content; (3) The shear strength index and failure strength of the compacted loess decrease with the increase in the initial moisture content, and increase with the increase in the compaction degree; (4) The failure strength of the compacted loess is positively proportional to the content of micro and small pores; while it is inversely proportional to the content of medium, large, and extra large pores and the average perimeter and area of pores. Keywords: loess; initial moisture content; compaction degree; shear strength; pore characteristics

Abstract:The decision tree model was used in this study to assess the landslide susceptibility in Yongjing County over a long time scale of nearly 40 years based on land use over five periods. Evaluation results show that the extremely high and high susceptibility zones of landslide disasters are mainly concentrated around the Yellow River basin (from Yanguoxia Town to Liujiaxia Hy ^-dropower Station) in the middle of the study area, the adjacent areas around Chuancheng Village-Hongquan Town-Wangtai Township in the southwest of the study area, and Santiaoxian Township in the middle east of the study area. The region is densely populated with many human activities. The results of this study are similar to those of previous studies, and the accuracy test with the receiver operating characteristic curve shows that the evaluation results of the five phases are highly reliable. In addition, a negative correlation is observed between the natural vegetation and bare land in the study area and the landslide susceptibility index, while the areas with frequent human activities, such as dry cropland, river area, and urban and rural construction lands, are likely to cause landslide disasters. From the perspective of time, the area of the extremely high and high susceptibility zones decreased yearly, but the reduction rate of the area has significantly slowed down since 2000. The area of urban and rural construction land in the region increased, and that of vegetation decreased during the same period. Hence, the stability of slopes in the region was reduced, and the capability of some disaster prevention measures was weakened. This study provides a reference for disaster prevention and subsequent urban and rural land planning in this area.

Abstract:Actual seismic weak links of rural houses were analyzed to understand the seismic performance of rural houses in the southeastern region of Gansu Province to improve their seismic capacity scientifically and reasonably. Combined with local survey data，various attribute data of rural houses in the study area were obtained through field survey，and main structural types，distribution characteristics，and proportion of rural houses were divided. The seismic performances of different types of rural structures were evaluated，and their weak seismic links and potential hazards were also analyzed. Results show five typical types of building structures in the study area: civil structure, brick-wood structure, brick-concrete structure, wood frame structure, and cave; most of these structures are the first three types. Among them, the seismic performance of newly-built brick-concrete and brick-wood structures with seismic construction measures is the best, followed by a wood frame, old brick-concrete, and brick-wood structures. The seismic performance of civil structures and caves is the worst. The research results have scientific reference value for improving the seismic fortification level of rural houses in southeastern Gansu and other regions.

Abstract:A large number of surface structures along active faults are damaged during earthquakes.Accurate estimation of the surface displacement induced by fault dislocation is critical as it accounts for the damage to surface structures. A valid asperity dislocation model helps calculate surface displacement more accurately. To examine how asperity heterogeneity affects surface displacement, this paper proposed an improved asperity dislocation model that considers the non-uniformity of asperity dislocation based on traditional asperity dislocation models. To validate the proposed asperity dislocation model, we chose the 1989 Loma Prieta earthquake as a target event. Surface displacements that induced the Loma Prieta earthquake under different asperity models were calculated. Results were compared with actual surface displacement measurements obtained by inversion. An area of 43 km ²calculated by the proposed non-uniform asperity model demonstrates a difference in surface displacement exceeding 8 cm compared with actual results, which is reduced by 25 %compared with the results derived from the uniform asperity dislocation model. The area with a difference in the horizontal surface displacement exceeding 8 cm is 117 km, which is reduced by 31 %compared with the results derived from the uniform asperity dislocation model. Furthermore, this paper applied the proposed non-uniform asperity dislocation model to calculate the surface displacement induced by the 1679 Sanhe-Pinggu M8.0 earthquake. Areas with surface displacements greater than 1 m and 2 m were summarized, and the maximum horizontal and vertical surface displacements were calculated. Outside Beijing, the maximum vertical and horizontal surface displacements occur near Sanhe City and exceed 4.8 m and 2.6 m, respectively. In Beijing, the maximum vertical and horizontal surface displacements appear in Tongzhou and the Pinggu District, which exceed 1 m and 2.6 m, respectively. The research results provide a reference for future seismic fortification in Beijing.

Abstract:The juncture of Shanxi,Hebei,and Inner Mongolia is located at the border area of the North China Block,Ordos Block,and Yanshan Block.The seismicity of this area,which is affected by the change in the tectonic stress,is related to future moderately strong earthquakes.The earthquake prediction index extracted from the observation data is a parameter with a certain physical significance,which has some degree of abnormal changes before an earthquake.The construction of the earthquake prediction index system is one of the most effective prediction methods in the empirical prediction stage.The earthquake frequency,which reflects the changes in the seismicity level and stress level,is a commonly used earthquake prediction index.Since 2019,there has been a significant enhancement of M L ＞3.0 earthquakes in the border area of Shanxi,Hebei,and Inner Mongolia.To evaluate the earthquake precursor significance of the seismicity in this area and build an effective prediction method, the enhanced area was selected as the window of earthquake frequency, and the annual moving frequency of M _L ＞3.0 earthquakes was taken as the prediction index. The optimal prediction rule was determined by tracing back the seismicity before previous M _L ＞5.0 earthquakes. Through a spatial scanning of the parameters of the prediction rule and taking the R value as the objective function, the prediction window length and threshold were finally determined to be 2 years and 14 times, respectively. The earthquake frequency prediction index for the proposed rule has a good prediction effect and high reliability. Keywords: seismicity enhancement; prediction efficiency; juncture area of Shanxi, Hebei and In-

Abstract:The risk for urban earthquake disasters has aggravated. Hence，the need for the establishment of a service system for earthquake disaster risk prevention and control has never been more urgent. This study analyzed the major challenges and actual level of the prevention and control of earthquake disaster risks in Tianjin. On the basis of the work that had been completed on the prevention and control of earthquake disaster risks in Tianjin，we focused on the research achievements and key techniques of earthquake risk investigation and assessment，earthquake disaster risk investigation and assessment，and earthquake disaster risk early warning. On this basis，with the problem，demand，and goal orientations of Tianjin earthquake disaster risk prevention and control，we propose establishing an earthquake disaster risk prevention and control service system with the investigation，assessment，governance，and service of earthquake disaster risk as the main line. Furthermore，we provide two major suggestions supporting service systems for the prevention and control of urban earthquake disaster risks in Tianjin during the "Fourteenth Five Year Plan" period.

Abstract:In 2019,the Beiliu M S 5.2 and Jingxi M S 5.2 earthquakes occurred successively in Guangxi,China,with an interval of only one month,which is a rare phenomenon since earthquake records began in Guangxi.In this study,the Coulomb failure stress changes of the Beiliu M_S 4.2 foreshock to its M_S 5.2 mainshock,Jingxi M S 5.2 mainshock to its M_S 4.3 aftershock,and Beiliu M_S 5.2 earthquake to the Jingxi M_S 5.2 earthquake were calculated.The results show the following: The Beiliu M_S 4.2 foreshock may have an obvious dynamic and static stress-triggering effect on the M_S .2 mainshock.The Jingxi M_S 5.2 mainshock may have a dynamic stress-triggering effect and static Coulomb stress-restraining effect on the M_S 4.3 aftershock.The occurrence of the Jingxi M_S 4.3 aftershock may be the result of the combined action of the tectonic stress field and dynamic stress triggering of the M_S 5.2 mainshock.Because of the small magnitude and long distance,the Coulomb stress-triggering effect of the Beiliu M_S 5.2 earthquake on the Jingxi M_S 5.2 earthquake is not obvious.

Abstract:In this study,the RISP system was used to obtain the real-time automatic detection results of the Maerkang,Sichuan earthquake sequence from 0:00 to 12:00 on June 10,2022.The automatic detection results were then analyzed and compared with the manual positioning results.The comparison results revealed that the number of earthquakes in the automatic catalog was 1.98 times that in the manual catalog,and the matching rate was 93.2 %.Earthquakes with an occurrence time deviation of less than ±1.0 s accounted for 95.64 %; those with an epicenter position deviation of less than 10 km accounted for 97.09 %; and those with a magnitude deviation of less than ±0.3 accounted for 96.36 %. The earthquakes detected and missed by the RISP system, as well as those with large deviations in earthquake parameters from the manual catalog, were analyzed. The advantages and disadvantages of the system for detecting dense earthquake sequences were summarized, and preliminary suggestions for optimizing the system were given. The RISP system can quickly produce the high-precision arrival date of the seismic phase and earthquake catalog with high completeness. Such information can be used for the determination of postearthquake trends and focal mechanism nodes, the rapid and precise positioning of aftershocks, and other earthquake emergency work. Therefore, the RISP system can quickly obtain high-precision seismic phase arrival data and the complete earthquake catalog and can thus be applied in earthquake emergency response work.

Abstract:In this study,a GIS-based selection method for disaster investigation points on earthquake sites was proposed to improve the efficiency of disaster investigation on earthquake sites,enhance the scientific and rational selection of disaster investigation points,and ensure the rapid and efficient development of the disaster investigation of earthquake sites.First,the urgency and timeliness of the disaster investigation task on earthquake sites were fully considered.Then,the GIS spatial analysis function was adopted in combination with the characteristics of earthquake sites, i.e., large investigation area, tight disaster investigation task, and limited personnel. Finally, basic geographic data were subjected to spatial-temporal analysis, and the selection method for disaster investigation points on earthquake sites based on GIS was then studied and formulated. Results showed that a reasonable and correct disaster investigation method for earthquake sites can help field disaster investigators conduct disaster investigation quickly and scientifically , thus greatly improving the efficiency of on-site disaster investigation and minimizing investigation time to the greatest extent. The proposed method can provide a sufficient time guarantee for the preparation of earthquake intensity maps and disaster loss assessment reports.

Abstract:In this paper,the three-dimensional coseismic deformation field of Changning M s 6.0 earthquake in Yibin,Sichuan Province on June 17,2019 was obtained by using the differential interferogram images of ascending and descending Sentinel-1A satellite.Then,the coseismic de-formation data was taken as the constraint condition, and the inversion results based on the Okada elastic half-space dislocation model show that the seismogenic fault conforms to the characteristics of strike slip and thrust. The fault rupture scale of the M _S 6.0 earthquake is about 15 km ×20 km; the dip and rake angles are 44.37^°and 56.42^°, respectively; the focal depth is about 10.2 km, and the moment magnitude is M _w 5.8. Finally, the SBAS-InSAR technique was used to obtain the cumulative deformation of the study region from April 5 to August 3, 2019. The results show that the near-field deformation fluctuation of this region is small before the earthquake, and the cumulative deformation increases after the earthquake. The reason may be that the distribution of aftershocks makes the surface change in an unstable state. Through a comparison with the existing research literature and the analysis of the fault structure in the study area, this study inferred that the Changning earthquake is caused by the sliding of seismogenic fault. The upper edge of the sliding surface is close to the ground surface, and the secondary fault activity caused by the mainshock triggers frequent strong aftershocks in a short time.

Abstract:In this study,the structural morphology of the central segment of the LiaochengLankao fault and the relationship between its active characteristics and the tectonic stress field were explored.We first collected the focal mechanism data on 46 earthquakes ≤ft(2.0 ≤slant M L ≤slant 4.4\right) in the study area and performed seismic moment tensor overlay analysis to solve the overall focal mechanism. Results showed that the fault in the study area was a strike-slip fault with a thrust component. Then, we obtained the optimal stress field parameters in the study by using the grid search method and found that the strike angle and inclination angle of maximum compressive stress axis σ₁were 13.57^°and 12.89^°, respectively; the strike angle and inclination angle of medium compressive stress axis σ₂were 274^°and 36^°, respectively; the strike angle and inclination angle of minimum compressive stress axis σ₃were 120^°and 51.05^°, respectively; and the stress ratio R was 0.8. Second, the strike angle and dip angle of the fault were fitted by using the position of small earthquakes to investigate the fault morphology and were found to be 218.5^°and 84.43^°, respectively, and the rake of the fault was estimated to be 55.7^°on the basis of regional stress field parameters. Finally, on the basis of the combination of the stress characteristics of the study area and the stress distribution on the fault plane, we concluded that the middle segment of the Li aocheng-Lankao fault was mainly subjected to the tension in the NWW-SEE direction and the horizontal compression of the stress field in the nearly NNE-SSW direction. Under the action of this stress field, the fault moved in a mode of left-lateral strike-slip with a certain thrust component. This study provides more accurate information on the stress field in the study region. Such information is convenient for future research.

Abstract:Influencing factors and burial types play an important role in the precursor analysis of groundwater observation data.In this study,on the basis of the air pressure,rainfall,and water level data of two wells in the Ganyanchi pull-apart basin of Haiyuan,namely,the GYC and GYCN wells,the influencing factors of water level change were analyzed,and the burial types of groundwater were studied by using three methods: the step response function,frequency spectrum analysis,and phase advance/phase lag of the tidal wave group method.Results showed that (1) air pressure and rainfall are the primary factors affecting the dynamic variation in the water levels of the two wells.(2) As a result of circulation for a long period,disrepair,casing damage,and the great effects of surface water,the burial type of groundwater in the GYC well is mixed water,which is inconsistent with the type of confined water recorded in historical data.The groundwater of the GYCN well is confined water. The research results provide a scientific basis for the access (exit) mechanism of the water levels of observation wells and the position of future observation wells in the study area. Furthermore, the findings are of great significance for anomaly identification and earthquake situation tracking in the future.