Abstract:Offshore oil-drilling risers have large length-to-diameter ratios and thin walls. The effect of residual stress is often neglected in the dynamic test on the vertical bearing capacity of risers, which leads to low accuracy of results. Based on a practical project, field dynamic test and wave fitting method were adopted to calculate the bearing capacity of risers. The dynamic characteristics of a riser-soil system and mechanism of residual stress generation and action under continuous hammering were analyzed, and the analysis method of residual stress was presented. Calculation and comparative analysis of bearing capacity, compressive stress, and tensile stress were performed, and the calculation results considering residual stress reflect well the actual stress state of the riser-soil system and effectively correct the error caused by the overestimation of upper soil resistance and underestimation of lower soil resistance, and the accuracy of bearing capacity and stress distribution can be improved. The results show that the bearing capacity of risers considering residual stress is slightly higher than those without residual stress. Compressive stress is lower in the upper part and higher in the lower part of risers than that without considering residual stress, and the result on tensile stress is opposite that of compressive stress. Research results have practical importance in the safe application of risers in offshore oil-drilling engineering.

Abstract:Given the low efficiency of the parameter optimization of the isolation layer based on a classical genetic algorithm, a parameter optimization method for the isolation layer based on a coarse-grained parallel genetic algorithm was proposed in this paper. Using the multiprocess mechanism of Python and the interaction between Python and ETABS, each core of the CPU can simultaneously perform ETABS to implement dynamic time-history analysis of isolation and nonisolation structures and use the CPU multiprocess to realize parallel genetic operation in genetic algorithms. According to the test results, compared with the original design results, the isolation structure optimized by a coarse-grained parallel genetic algorithm has a better performance. Meanwhile, compared with the classical genetic algorithm, the proposed method can not only accurately obtain globally optimal solutions but also substantially improve the optimization efficiency. The speedup ratio is approximately 6, which can meet the prompt demand for design in isolation engineering. Therefore, this method has a notable application potential.

Abstract:To study the progressive collapse resistance of concrete-filled steel tube (CFST) structures with different forms of concentrical brace, five numerical models of a CFST frame-concentrically brace structure were established based on the fiber beam model. Based on the reasonable steel and constitutive model of concrete materials, the nonlinear dynamic response of the structure under different failure conditions was calculated, and the overall stiffness and ultimate bearing capacity of the structure were obtained by nonlinear static loading. The results show that different brace forms can effectively improve the overall stiffness and anti-collapse bearing capacity of the structure, and the improvement effect under corner column failure condition is better than that under other failure conditions. A new load transfer path can be provided by setting braced frame, which can effectively reduce the distributed internal force of adjacent members of failure columns. X-brace can obviously improve the stiffness and bearing capacity of the frame under any failure condition and reduce the vertical displacement of failed joints. The anti-inclined brace frame shows better ductility and ultimate bearing capacity than others. The above research results can provide a reference for the design of building structures to resist the progressive collapse.

Abstract:The Hefei-Wuhan section of the proposed Shanghai-Chongqing-Chengdu high-speed railway intersects with the Macheng-Tuanfeng fault near Huangtuzui, Macheng City in northeastern Hubei. Comprehensive analysis of previous materials was used as the basis, and through field geological survey, shallow seismic exploration, and geological drilling, the accurate spatial distributions and fault properties of the intersection of the Macheng-Tuanfeng fault and the proposed line were identified. Moreover, fault activity and its possible impact on the proposed line were comprehensively analyzed. According to research results, the intersection of the Macheng-Tuanfeng fault and the proposed line still belongs to the north section of the Macheng-Tuanfeng fault, which has two branches in the east and west and is composed of three hidden faults. The NNE-trending thrust faults on both banks of Yanjiahe River are the west branch of the north segment of the Macheng-Tuanfeng fault, which is the main part of the fault, and one NE-trending fault on the east side is the east branch of the north segment of Macheng-Tuanfeng fault. The Macheng-Tuanfeng fault in the study area is a fault in the mid-late Pleistocene with weak activity. However, the fault has tectonic background and seismotectonic conditions for earthquakes with a magnitude of approximately 6. When the proposed line crosses this fault, earthquake-resistant and early warning measures need to be considered. This study provides engineering measures and suggestions for the engineering design and construction of subsequent lines.

Abstract:Creeping diseases often occur in curved girder bridges in service. To explore the influence of creeping disease on the seismic performance of curved girder bridges, we summarized creeping diseases and used various creeping displacements at the girder end as comparative analysis conditions. A three-span prestressed concrete curved girder bridge was used as an example, and the finite element model was established using MIDAS Civil. The effects of pile-soil interaction, bidirectional pounding effect, and material nonlinearity were considered in the analysis of seismic responses of the main members of the curved girder bridge, such as bearings and piers, and the influence of the creeping state on the seismic performance of the bridge was discussed. The results show the adverse effect of creeping diseases of the main girder on the seismic performance of the bridge, leading to the expansion of bearing displacement and increased risk of bearing damage. As a result, the pounding effect of the bridge superstructure and the risk of beam falling increased. With the increase in creeping displacement, the damage state of the bridge pier may change from no damage without considering creeping to a serious damage state when creeping is considered. Therefore, the evaluation of the seismic performance of curved girder bridges in service and creeping state should be quantified, and reasonable measures should be implemented to limit the main girder creep.

Abstract:Mountainous and hilly topography affects the distribution of ground motion. The study of topographical effect enables the complete understanding of the risk of earthquake disasters and the implementation of preventive measures to reduce disaster loss. In this paper, a three-dimensional finite element model of the hill where the Zigong topographic array is located was established based on actual topography. A preprocessing program for setting viscoelastic artificial boundaries and vertical incidence of the SH wave was developed to carry out dynamic numerical simulations. The rationality of the proposed model was verified through the comparison of numerical simulation results with actual records. Analysis was conducted to determine the influence of low mountains and hills on the intensity and spatial distribution of ground motions and the relationship among peak ground acceleration and wave frequency, elevation, and slope. The results show the amplification effect of the top of the low hill on the peak ground acceleration, which is weakened by concave topography at the foot of the hill. The topographical effect is closely related to the frequency of input ground motion, and input ground motions with different dominant frequencies cause varied distributions of peak ground acceleration. A good positive correlation was observed between peak ground acceleration and elevation, but a weak correlation between peak ground acceleration and slope. The fitting effect of peak acceleration through the combination of elevation and slope is better than that when using only elevation or slope. The binary third-order polynomial exhibited a desirable fitting effect, which can be used to quantitatively describe the changes in topographical amplification coefficient with elevation and slope.

Abstract:A typical plank road in Cave No. 154 was selected to investigate the dynamic response of pedestrian plank roads in the Maijishan Grottoes. A three-dimensional solid model was created using ABAQUS. Given the seismic environmental characteristics of the Maijishan Grottoes and based on the results of seismic risk assessment in the Maijishan Grottoes area, the acceleration response, stress, and damage distribution of the plank road under earthquake action corresponding to 50-year exceedance probabilities of 63.5%, 10%, and 2% were analyzed, and the seismic performance levels of the plank road structure were classified. The results show that the inclined ladder of the plank road structure had a considerably greater acceleration response than the platform plate under earthquake action. The peak acceleration response increases with the height of the platform plates. The concrete at the end of the cantilever beam, which is embedded in a rock mass, has a relatively high stress. The stress in the steel bars at the intersection of the inclined ladder beam and cantilever beam is relatively large. With the increase in earthquake action, the range and numerical value of tensile and compressive damage to the concrete of plank road structure increases and is mainly concentrated at the end of the cantilever beam embedded in the rock mass, showing typical failure characteristics of upper tension and lower compression. Based on the stress and strain of the material and the damage degree of components, the seismic performance level of the plank road is classified. The seismic damage assessment results of the plank road under frequent (PGA=70 gal) and design (PGA=240 gal) earthquakes reveal mild damage, and under rare (PGA=450 gal) earthquakes, the seismic damage assessment results indicate severe damage. The research results can provide a scientific basis for seismic damage assessment and reinforcement design of plank roads in the Maijishan Grottoes.

Abstract:On January 8, 2022, an M_S6.9 earthquake occurred in Menyuan County, Qinghai Province. The earthquake caused damage to the Daliang tunnel of the Lanzhou-Xinjiang high-speed railway near the epicenter, resulting in a long-term shutdown of the high-speed railroad. In this study, a two-dimensional plane strain model was established to conduct a dynamic time-history analysis under the loading of bidirectional Menyuan seismic waves. The seismic response results of the Daliang tunnel were obtained, and the deformation and seismic damage characteristics of the model after the earthquake were analyzed in detail. The results show that the seismic response of the Daliang Tunnel was substantially affected by the horizontal seismic load under the bidirectional loading of Menyuan seismic waves. The cross-sectional shape of the tunnel strengthened the seismic responses of vertical displacement and acceleration along the y-axis. The largest seismic responses were observed in the tunnel vault. The vertical and horizontal seismic accelerations were 5.206 4 and 4.534 8 m/s², respectively. The vertical and horizontal displacements were 7.070 9 and 0.641 5 cm, respectively. The smallest seismic responses were detected at the arch bottom. The vertical and horizontal seismic accelerations were 3.287 6 and 4.511 2 m/s², respectively. The vertical and horizontal displacements reached 4.851 6 and 0.625 2 cm, respectively. An evident stress concentration occurred at the spandrel and arch foot, and the stress forms of internal forces changed at the vault, arch bottom, spandrel, and arch foot. However, the extreme values of stress and internal force of lining occurred in the arch waist and arch foot, indicating that these areas are severely damaged by earthquakes and should be given special attention during repair after earthquakes.

Abstract:Peaty soil is a special regional soft soil. Structures with peaty soil foundations are prone to produce large postconstruction settlements, largely affecting their safety. Thus, it is crucial to study the settlement of peaty soil. The settlement can be divided into three parts, which are as follows: settlement caused by lateral deformation, settlement under the confined condition, and secondary consolidation settlement. Based on the Duncan-Zhang constitutive model, the relationship between compression modulus and secant modulus was established. Combined with the generalized Hooke's law derivation, the settlement caused by lateral deformation was determined. The compression moduli of soil were calculated by the e-p, e-lgp, and e-lnp curves, and the settlement under the confined condition was calculated using the layer-wise method. Furthermore, a high-pressure consolidation creep test was performed on peaty soil. The secant modulus was calculated by the Duncan-Zhang model concept, and the nonlinear correction was performed on the original five-element rheological model. Subsequently, the original and nonlinear models were modified by the introduction of the correction coefficient φ_s. The two modified models were utilized to fit the creep test curves, and it was found that the fitting effect of the modified original model was very poor; moreover, the correlation coefficients of the modified nonlinear model were all greater than 0.9 and a constitutive equation suitable for describing the creep of peat soil was also obtained. Lastly, the two modified models were used to calculate the secondary consolidation settlement with the layer-wise summation method. It was revealed that the settlement calculation results of the peaty soil are consistent with the actual experiment results, confirming the rationality of the calculation results as well as providing a calculation theory and a constitutive model to reflect the creep characteristics of peaty soil.

Abstract:Under earthquake action, the pounding between adjacent main beams can change the dynamic response of an abutment-approach bridge-rigid frame continuous girder bridge system. To explore the influence of structural parameters (structural form of main bridge, pier height, span number of approach bridge, expansion joint spacing, etc.) on the pounding effect at expansion joints and seismic response of bridge structure, we considered an actual prototype bridge as a research object. We considered the dissipation of pounding energy, the interaction between pile and soil, and the interaction between abutment and backfill behind abutment and established the nonlinear behavior of bearing and pier, a finite-element model of the abutment-approach bridge-rigid frame continuous girder bridge structure system was established using CSiBridge, and elastic-plastic dynamic analysis was carried out. The analysis results reveal that the stress of the main pier varies with the different structural forms of the main bridge, and the stress of the continuous girder bridge becomes more reasonable when the height difference between adjacent main piers increases. With the increase in pier height, the dynamic difference between the main approach bridges increases, and the pounding effect becomes more significant. The increased number of spans of the approach bridge and the increase in the spacing between expansion joints cause the pounding effect at the expansion joints to increase and decrease, respectively. The enhancement and weakening of the pounding suppression effect also cause the decrease and increase in the internal force and deformation of rigid frame piers, respectively, but have a negligible effect on other piers.

Abstract:For the high-filled cut-and-cover tunnel (HFCCT) constructed in the loess plateau of Northwest China, laying the expanded polystyrene (EPS) plate on the top of the cut\|and\|cover tunnel (CCT) effectively reduces the earth pressure around the CCT and ensures structural safety. However, given the high dynamic sensitivity of the backfill, earthquakes will disturb the stabilized backfill and cause considerable changes in the earth pressure around the CCT, thus adversely affecting the CCT. In this paper, the numerical simulation method is used to study the characteristics of earth pressure change and soil arching effect around the HFCCT under earthquake action. The results show that under seismic action, although the soil arching effect triggered by load reduction of the EPS plate remains, it weakens with the decline in soil arching height. The variation trends of the time\|history curves of vertical dynamic earth pressure are consistent in the range of 0-5 m from the center of CCT, and the opposite is observed in the range of 5-7 m from the center of CCT. When the vertical dynamic earth pressure at the top of CCT reaches the peak value, the average vertical dynamic earth pressure is 1.14 times the average vertical static earth pressure. The opposite change trends of the time\|history curves of horizontal dynamic earth pressure occur on both sides of CCT. When the horizontal dynamic earth pressure reaches its peak value, the average horizontal dynamic earth pressure is 2.89 times the average horizontal static earth pressure.

Abstract:Previous earthquake damage showed that earthquakes greatly affected underground structures, such as tunnels. When the dominant frequency of ground motion is consistent with the natural frequency of the structure, the resulting resonance will cause serious structural damage. Aiming at the resonance characteristics of shallow-buried bias loess tunnel during earthquakes, harmonic response analysis in ANSYS is conducted to study the resonance response of tunnel lining and variation law of the peak value of resonance response from the surrounding rock to the lining under bidirectional coupling earthquake, and the influence of bias angle and maximum span of section on peak resonance response is discussed. Results indicate the multiorder natural frequencies of the shallow-buried bias loess tunnel. In addition, the displacement and stress of the lining exhibit a resonance phenomenon without the natural frequency characteristics of the structure. The resonance response from the surrounding rock to the lining exhibits an amplification effect. The peak value of horizontal displacement decreases with the increase in bias angle. An appropriate increase in the maximum span of the section is beneficial to seismic resistance. The Arch waist and arch foot should be strengthened in the seismic design of the tunnel because resonance greatly affects principal stress.

Abstract:The swimming pool reactor (SPR) is a new type of environment-friendly heating source. The seismic response of a reactor building under diverse foundation conditions is the crucial technical reference for its seismic design. A certain SPR building was considered as the research object, and the three-dimensional dynamic interaction model of SPR foundation considering the liquid sloshing effect was established based on ANSYS software and secondary development characteristics of UPFs. The energy dissipation of scattered waves was considered by creating viscoelastic boundary elements, and the dynamic hydraulic effect was simulated using the Housner equivalent mechanical model. Thus, an impact analysis of diverse foundations on the seismic response of the SPR building structure was carried out. The analysis results reveal that the seismic response of the SPR changes considerably when the hardness and stiffness of the foundation decrease gradually, particularly when the lithologic foundation progressively changes into the soil foundation, the principal stress and story drift ratio of the structure increase progressively, and the acceleration response spectrum gradually reduces. The research production can offer a beneficial reference for the seismic design of various SPRs.

Abstract:To further gain insights into the dynamic characteristics and seismic performance of integral bridges, we established a finite-element model of abutment-soil entity and proposed a reasonable mathematical model for abutment-soil interaction. Then, the Midas Civil overall model was used to study the influences of abutment-soil interaction, pile-soil interaction, and pier structure on the seismic performance of integral bridges. Results show that compared with simply supported beams, the longitudinal stiffness of an integral bridge with the same span was considerably improved, but the difference between lateral stiffness was small. The constraint stiffness of soil behind the abutment showed no evident influence on the static and dynamic characteristics of the bridge, and the calculation of the seismic force behind the abutment of the integral bridge is relatively conservative according to the existing code in China. Increasing the lateral stiffness of bridge piers and changing single\|pillar piers to double-pillar piers can greatly improve the seismic performance of the structure. The research conclusions of this paper and the calculation method of the coefficient of earth pressure behind abutment can provide references for the seismic calculation of integral bridges.

Abstract:The mechanical behavior of lintel-column joints in antique buildings can be improved by adopting a steel-concrete composite structure and setting viscous dampers at the Queti. For the study of its mechanical properties, three specimens were designed and tested, namely, two specimens with viscous dampers and one specimen without viscous damper for comparison. The failure process and mechanism of the lintel-column joints in antique buildings were analyzed using the three specimens under dynamic cyclic sine wave loading. Based on the experimental results, the mechanical properties of the lintel-column joints were analyzed, including the restoring force characteristic curve, skeleton curve, and changes in ductility and stiffness. The results indicate that the seismic behavior of the lintel-column joints in antique buildings with steel-concrete composite structures was improved to a certain extent. The beam hinge mechanism was formed when the structure was damaged, which meets the seismic design requirement. Viscous dampers at the Queti can enhance the bearing capacity and deformation performance of joints and restrain the stiffness degradation rate of the specimen to a certain extent. Overall, the general seismic performance of the structure has been greatly improved.

Abstract:Foundation conditions and wall height affect the seismic response of retaining walls. In this study, a finite element time-history analysis model of inclined retaining walls on different foundations was established to study the influence of foundation condition and wall height on the dynamic response of retaining walls and wall-soil interaction in the most unfavorable moment. To meet the requirements of mechanical calculation and wall displacement limit, we proposed the height control of the inclined retaining wall considering the foundation condition and peak ground acceleration (PGA). The results show that the dynamic earth pressure of the retaining wall on the rock foundation was large in the middle and small at both ends, showing a convex shape along the wall height. In addition, the earth pressure under large earthquakes was reduced slightly compared with that under medium earthquakes. The contact pressure beneath the foundation was zero at the wall heel and concentrated at the toe, and this finding became more evident with an increase in PGA and wall height. For the retaining wall on the soil foundation, the backfill behind the wall followed the wall movement owing to the traction effect caused by the deformation of the foundation soil. The dynamic earth pressure at the back of the wall was positively correlated with PGA and approximately linearly distributed along the wall height and was the largest at the wall bottom. The reciprocating motion of the retaining wall made the plastic deformation at both ends of the base more important than that in the middle, and the peak value of reaction force was transferred to the middle. According to the calculation of stability and bearing capacity at the most unfavorable time and reasonable restriction on wall displacement, in the seismic area, the allowable height of the inclined retaining wall was 8 m when the PGA was less than 0.2g. Moreover, when the PGA was 0.4g, the allowable heights of the retaining wall on hard rock foundation, soft rock foundation, and gravel soil and sandy clay foundation were 8, 6, and 4 m, respectively.

Abstract:To study the active earth pressure characteristics of lightweight soil, we conducted model tests on a large-scale rigid retaining wall. The displacement of the retaining wall was controlled to analyze the active earth-pressure distribution law of lightweight soil. The results show that the lateral earth pressures of lightweight soil first decreased and then gradually stabilized with increasing retaining wall displacement. When the displacement of the retaining wall was 3 mm, the lateral earth pressure of lightweight soil reached a stable state. The active earth pressure of lightweight soil was considerably less than that of remolded loess, indicating that the former can effectively reduce active earth pressure on the back of walls. The active-earth-pressure coefficient of lightweight soil ranged between 0 and 0.16, and a slight change range was observed along the height of the retaining wall. However, the active earth-pressure coefficient of the remolded loess was 0-0.57, which is evidently larger than that of lightweight soil. According to the comparative analysis of Rankine's theoretical and model test values, the Rankine active earth pressure of lightweight soil is less than the test value. The absolute error between the theoretical and experimental values was 0-6.32 kPa, which can be ignored in practical engineering. A certain friction existed between the wall back and fillings in the model tests. Therefore, Rankine's theory remains accurate in the calculation of the active earth pressure of lightweight soil. The active earth pressure characteristics of lightweight soil, which are important for improving the earth pressure theory of lightweight soil, were revealed by model tests and traditional theoretical analysis.

Abstract:Earthquake-induced landslides are one of the most common secondary geological hazards, and they not only deteriorate the environment but also result in severe casualties and property losses. Therefore, researchers have long been paying attention to this issue. To understand the development trend of studies on seismic landslides and refine scientific issues related to the quantitative evaluation of seismic landslides, this paper systematically summarizes the quantitative evaluation of regional landslides, including their origin, current state of development, existing problems, and prospects. The research findings indicate that (1) studies on quantitative evaluation of regional landslides emerged in the 1980s, and scholars have attained fruitful achievements after more than 50 years of unremitting efforts. To date, new social demands must be met by the quantitative evaluation of regional earthquake landslides. (2) Seismic landslide results from the coupling effect of multiple factors, including dynamics, geological characteristics, and geomorphic conditions. Seismic landslides can only be explained when the causes and dynamic processes are considered. Research on the causes and mechanisms of seismic landslides mainly focuses on the analysis of the dynamic response law of slopes under strong earthquakes. (3) Fundamental studies on development characteristics, causes and mechanisms, and database construction of seismic landslides have promoted research on the quantitative risk evaluation of landslide disasters, which includes the quantitative assessment of the hazard, vulnerability, and harm of seismic landslides. (4) In the quantitative evaluation of regional landslide disasters, it is necessary to further explore the systematic formation and spatiotemporal distribution patterns of regional landslides, improve and refine the methods for quantitative evaluation of regional landslide risks, and explore the strategies and plans for regional landslide disaster prevention and control.

Abstract:Two M_S6.4 and M_S5.1 successive earthquakes occurred in Kashgar, Xinjiang, on January 19, 2020, and February 21, 2020. Based on the statistical analysis of 128 strong ground-motion data records collected by the Xinjiang strong ground-motion data network, the amplitudes and spectral response characteristics of the two earthquakes were investigated. Then, the obtained results were compared with the spectral responses of two current codes. The results show the following: (1) For the same earthquake magnitude, the spectral acceleration response increases and its attenuation speed decreases as the epicentral distance decreases; for the same epicentral distance, the spectral acceleration response increases and its attenuation speed decreases as the earthquake magnitude increases. (2) When the earthquake magnitude increases, the spectral acceleration, spectral ground velocity, and spectral ground displacement increase. (3) The spectral acceleration responses and their average curves of the M_S6.4 and M_S5.1 earthquakes are similar; however, they are quite different from the spectral acceleration responses of the current codes in China. It is recommended that the spectral acceleration response based on local strong earthquake data records should be used in the seismic design of structures in Kashi, Xinjiang.

Abstract:In the alternating current (AC) observation of the geoelectrical resistivity, the observation accuracy is affected by the inductive coupling effect. Theoretical studies have shown that the inductive coupling effect is related to the electrical frequency, the distance between the current circuit and the potential circuit, and the parallel length of the two circuits. To verify the consistency between the theoretical and experimental observation results, we rearranged the wiring paths of the electrodes and conducted an AC geoelectrical resistivity observation experiment at the Gaoyou seismic station in Jiangsu Province. The results show that when the parallel lengths of the circuits and the electrical frequency decrease, the inductive coupling effect is reduced. Also, when the distance between the circuits increases, the inductive coupling effect is reduced. These results support our theoretical analysis. In addition, the effects of parallel length and distance between circuits on the inductive coupling effect can be ignored when the electrical frequency is below 0.5 Hz. When the electrical frequency increases to 1 Hz, it is necessary to avoid the inductive coupling effect by decreasing the parallel length or increasing the distance between circuits.

Abstract:The determination of the geometry of an active fault provides an important theoretical basis for assessing the seismic risk of a region. The structural background of the Xingtai earthquake zone is complicated. Many previous studies on the seismogenic structure of the Xingtai earthquake have been conducted, and plenty of results have been reported. In this paper, we evaluate the strike and dip angles of the seismogenic fault of the Xingtai earthquake as well as their standard deviation by clustering nodal planes of focal mechanisms. Then, the average solution of the seismogenic fault plane is obtained by synthesizing the previous results. Finally, using the crustal stress tensor in the region under investigation, we estimate the sliding direction and its standard deviation and analyze the seismic activity risk. The calculated values of the strike, dip, and rake angles of the seismogenic fault are 32.45°, 79.44°, and -153.96°, respectively, with a standard deviation of 4.55°. These values indicate that the fault under investigation is a high\|dip angle strike\|slip fault extending from NNE to NWW rather than a normal Xinhe fault. The estimated relative shear and normal stresses applied to the fault are 0.83 and 0.59, respectively. These values are based on the regional stress field. The shear stress applied to the fault is high, indicating that the fault is essential in the accumulation and release of seismic energy.

Abstract:On September 12, 2018, an M_S5.3 earthquake occurred in Ningqiang County, Hanzhong City, Shaanxi Province, with a focal depth of 11 km. Based on the geophysical data obtained during the period from 2014 to 2018 in the Shaanxi region, 20 observation stations monitoring the groundwater level, cave strain, volumetric strain, and geoelectric field are selected, and the load/unload response ratio (LURR) of each station is calculated using the Coulomb stress triggered model. The abnormal information obtained before the M_S5.3 earthquake is analyzed, and the following preliminary conclusions are extracted: (1) LURR anomalies appeared in the period from the end of 2017 to May 2018, during which the LURR of the groundwater level exhibited the earliest abnormal variation and the earliest maximum value. The LURR anomalies in the cave strain, volumetric strain, and geoelectric field appeared relatively late, from February to May 2018, and their maximum values were observed from March to July 2018. (2) The abnormal variation range of various observation elements shows that the variation range of the groundwater level is the smallest, the variation range of the geoelectric field is larger than that of the groundwater level, and those of the cave and volumetric strains are the largest. The abnormal stations with different measurement elements exhibit a relatively spatial concentration. (3) The abnormal variations of LURR and the dominant azimuth of the Zhouzhi geoelectric field are relatively synchronous in the time domain. (4) Generally, the abnormal evolutions of LURR obtained from the geophysical data of the groundwater level, cave strain, volumetric strain, and geoelectric field are quasi-synchronous. These findings provide a reference for calculating LURR from various observation data, are mutually verified by multiple physical quantities, and improve the reliability of abnormal information.

Abstract:Based on the data of the Menyuan M6.9 earthquake and 680 aftershocks recorded by 87 seismic stations in Qinghai Province and its adjacent areas from January 8 to 13, 2022, the earthquakes were relocated by the double-difference location method, and the source parameters for 633 earthquakes were obtained. Results show that the distribution of aftershocks is divided into east and west sections, with the southern tip of the Changma-Ebo fault as the boundary. The west section is distributed along the eastern segment of the Tuoleshan fault in a nearly EW direction, and the east section is distributed along the western section of the Lenglongling fault in an NWW direction. The focal depths of aftershocks concentrate at 5-15 km before relocation, while those after relocation are normally distributed in a depth range of 0-20 km. According to the distribution characteristics of aftershocks after relocation and the distribution of the surface rupture zone, two rectangular areas were selected on the basis of the principle that cluster earthquakes occur near the fault. Based on the relocated focal information in the two areas, the fault plane fitting calculation was conducted using the simulated annealing and Gauss-Newton algorithms and the fault plane parameters of each fitting area were obtained. Results show the following: the fault plane in the eastern segment of the Tuoleshan fault is a high-dip left-lateral strike-slip fault with nearly EW direction and a length of approximately 15 km; the fault plane in the western segment of the Lenglongling fault is a high-dip left-lateral strike-slip fault with NWW direction and a length of approximately 12 km. This earthquake may be caused by the mutual extrusion and rupture of the ends of the two aforementioned fault planes.

Abstract:The Yangguan fault is located in the northern part of the Tibet Plateau, where the Altyn Tagh fault system extends northward. Further studies on its geometry and kinematics are needed to understand the extension mechanism of the Tibet Plateau to the interior of the continent. We investigate the Yangguan fault in detail using satellite image interpretation, trench excavation, differential GPS, and UAV survey. The results show the existence of multiple positive and negative fault scarps in the eastern part of the Yangguan fault; the height of fault scarps ranges from 0.4 to 8 m with an average of 2.2 m. The dip angle of the fault revealed by the trench is approximately 60°, forming high-angle reverse faults and locally developing normal faults. The western part of the fault extends to the NW front, forming a group of arc-shaped fault scarps; their height ranges of 0.9-2.4 m with an average of 1.9 m. From south to north, the pattern of the thrust fault scarps changes from multistage scarps to single scarps. The trench profile analysis results show that the fault dates to the alluvial-diluvial gravel layer of the Late Pleistocene age. The dip angle of the developed faults is relatively even, mainly characterized by a low angle thrust of approximately 26°; some faults even push forward along the formation. Combined with previous research results, the Yangguan Fault may be the northern boundary of the Altyn Fault's northward expansion, and it absorbs part of the strain in the eastern Altyn Fault in coordination with the Sanweishan fault.

Abstract:The investigation of the seismic capacity of buildings is of great significance to comprehensively understand the risk of earthquake disasters and predict the disasters caused by earthquakes. The traditional field investigation method is difficult to apply on a large scale, while the efficiency of the remote-sensing seismic capacity evaluation of buildings, which relies on empirical estimation and manual interpretation, needs improvement. To address the above issues, we propose a multiscale aggregated building extraction method based on a remote-sensing target recognition deep-learning algorithm. The proposed method is applied to the remote-sensing preliminary seismic capacity evaluation of buildings in Hubei Province. Over 10.6 million buildings are automatically extracted, and their seismic capacity is classified and determined. Compared with the field-investigation results in pilot counties, the overall error of building extraction using this method is less than 10%, and the evaluation accuracy of the seismic capacity of buildings is between 72.3% and 90.9%. The experimental results show that the proposed method can support the seismic capacity investigation of buildings in the framework of the national natural disaster risk census project.

Abstract:Many micro-events may be missed in earthquake detection due to the interference of coda waves after moderate-strong earthquakes, thus affecting the completeness of earthquake catalogue. In this paper, microseismic detection of the Jiashi M_S6.4 earthquake sequence was carried out using the matched filter method. 1 756 microseismic events were detected, which was 1.3 times more than the catalogue from China Earthquake Networks Center (CENC). The minimum magnitude of completeness of the detected aftershock catalogue is M_L1.2 and the b value of seismicity is 0.76, which are lower than those of the original catalogue (M_L1.6 and b=0.77). The characteristics of seismic sequence activities in Jiashi focal area were analyzed, and the results show that the foreshock sequence intensively strengthens within a short term (the first 36 hours) before the mainshock and the corresponding b value is low. The magnitude of completeness of the seismic sequence is high after the mainshock, then it slowly decreases and tends to be stable with periodic fluctuations. The study improves the completeness of the earthquake catalogue in Jiashi focal area, thus providing key data for a detailed description of the space-time evolution characteristics of the earthquake sequence in the region.

Abstract:Gravity data are indispensable in determining the source rupture model and obtaining preliminary earthquake information. To analyze the gravity variation caused by a dislocation on the earth's surface due to an earthquake, we calculate the gravity variation characteristics of a typical fault slip (strike- and dip-slip). Based on the results obtained using the Okubo dislocation theory formula, we observe the following: (1) the total gravity variation caused by vertical strike-slip faults exhibits a four-quadrant symmetrical distribution. The magnitude of the gravity variation at locations with the same azimuth near the epicenter gradually decreases with the distance from the fault; for the same rupture geometry and slip, the magnitude of the gravity variation near the epicenter decreases as the depth of the rupture center increases, while the magnitude of the gravity variation away from the epicenter exhibits a slower decrease. (2) The gravity variation at the hanging walls of the dip-slip fault is generally smaller than that at the footwall; for dip-slip faults with the same rupture geometry and slip, the maximum value of the gravity variation decreases with the distance as the depth of the rupture center increases. To analyze the gravity variation caused by the Menyuan earthquake in 2022, the coseismic rupture model of the earthquake is selected, and the total gravity variation around the epicenter is calculated by superimposing the gravity variations caused by subruptures. The results show that the gravity decreases in the northeast and southwest directions away from the epicenter; its minimum value is -8.82 μgal. Additionally, it increases in the northwest and southeast directions away from the epicenter; its maximum value is 28.28 μgal. The area where the gravity increases is smaller than the area where the gravity decreases.The gravity in the Menyuan station near the epicenter increases by 3.40 μgal, which can be monitored using gravity measurement instruments. The gravity variation measured by other stations located around the epicenter is less than 1 μgal. When monitoring and analyzing the long-term gravity variation in this region to reveal its tectonic activity, the gravity variation caused by the Menyuan earthquake should be deducted.