Abstract:There are few studies on the reliability analysis of loess multi-stage high fill slopes in Northwest China. In this paper, a loess multi-stage high fill slope in the study area was taken as the background. Considering the uncertainty of the distribution of loess filling parameters, several analysis models with different slope rates and different platform widths were established. The Monte Carlo simulation method was used to analyze the reliability of the loess multi-stage high fill slope, and the influencing law of the slope reliability was obtained. The research results showed that when the slope rate is between 1∶0.5 and 1∶1.0 and the platform width is between 0.5 m and 1.5 m, the change of the slope rate and platform width will have a great impact on the reliability of the loess multi-stage high fill slope. The research results provide a theoretical basis for the reliability research and application of loess multi-stage high fill slopes.

Abstract:A reliability analysis method for the seismic stability of collapse accumulation body, which both considers the bi-directional earthquake excitation and the uncertainty of rock and soil parameters, was proposed in this paper. The influence of horizontal and vertical seismic loads on the stability and reliability of collapse accumulation body was further analyzed. First, the safety and stability state of the collapse accumulation body under bidirectional earthquake was analyzed by using the pseudo static method and the limit equilibrium method, and the seismic limit state equation of collapse accumulation body was established based on the response surface method and the JC method. Then, the parameters of rock and soil were processed using the blind number theory, and the blind number model for the seismic safety factor of collapse accumulation body was further established. Finally, the corresponding program was compiled by MATLAB to realize the fast output of calculation and analysis results. The calculated results showed that: the calculation value of the proposed method is low, so it is more safe and reliable for projects. Compared with the horizontal seismic load, the vertical seismic load has little impact on the stability and reliability of collapse accumulation body, which only reduces the safety factor and reliability by 1.78% and 2.78%, respectively. Therefore, in this case, only the influence of horizontal seismic load needs to be considered when the quasi-static method is used for seismic analysis.

Abstract:There are more and more large-scale basic engineering projects in the western region of China. To deal with the earthwork excavated from the projects, reduce the project cost and achieve the goal of green development, the feasibility of red-bed soft rock improved soil as subgrade backfill was evaluated through experimental research. Based on the deep foundation pit project of a subway in Northwest China, the red-bed soft rock improved soil with different loess and cement mixing ratio were first studied by orthogonal test. Then, the influencing factors of the improved soil's compression modulus were analyzed, and the best mix proportion was given. Finally, the improved soil with the best mix proportion was tested before and after soaking to evaluate its water stability. The results showed that both loess and cement have significant effects on the compression modulus. The recommended optimum mix proportion of red-bed soft rock improved soil is 20% loess and 7% cement. The compression modulus of the improved sample increases gradually with the increase of curing time before soaking, and decreases with the increase of age after soaking. Loess not only improves the compression modulus and compaction effect, but also has no impact on the water stability. The above conclusions have a certain reference value for evaluating the feasibility of the improved red-bed soft rock as subgrade filler.

Abstract:The accuracy and applicability of horizontal seismic force of the railway girder bridge’s bearings under design earthquakes, which was calculated with the static method, were studied in this paper. The round-ended gravity piers of a railway simply-supported girder bridge with a pier height of 5-20 m and a span of 32 m was taken to established a single pier seismic model. The response spectrum method was used to analyze the horizontal seismic force of the bearings under different site conditions, and the reasonable stiffness value of pier section under design earthquake was discussed. The analysis results showed that the piers are cracked under design earthquake, so the stiffness of cracking section should be selected as the section stiffness when calculating with the response spectrum method. The design value will be too large or too small if using the static method to calculate the horizontal seismic force of bearing. With the decreasing height of pier, the site conditions become worse and the dynamic effect become more obvious. It is suggested that the horizontal seismic force of the bearing should be calculated by the dynamic method.

Abstract:In this paper, a model for the tunnel-soil-superstructure interaction under different site conditions was established, then the effects of superstructure, site conditions, and seismic wave spectrum characteristics on the seismic response of tunnel-soil-superstructure system were studied. The calculation results showed that: (1) The seismic response of underground structures such as tunnel is mainly affected by site conditions. The dynamic internal force of tunnel under different site conditions varies greatly, which should be paid enough attention in design. In contrast, the presence or absence of adjacent superstructure has little impact. (2) Under vertically incident S-wave, the dynamic internal force response of tunnel is symmetrical when there is no superstructure. The superstructure will break the symmetry, because the dynamic axial force at the 45° angle between the tunnel and adjacent superstructure is increased, and that at the 135° angle on the other side is significantly decreased. (3) The influences of wave spectrum characteristics on the seismic responses of overground and underground structures differ obviously. The overground structure is more affected by the input seismic wave than the underground structure, while the underground structure is mainly controlled by the site conditions.

Abstract:To study the seismic behavior of ultra-high performance concrete (UHPC)-normal concrete (NC) composite columns reinforced by high-strength steel bars, based on the finite element program ABAQUS, the relevant parameters of the damage plastic model were calibrated and a seismic finite element model of UHPC-NC composite columns reinforced by high-strength steel bars was established. The validity of the proposed model was verified by comparing with the pseudo static test results of three NC columns and three UHPC columns. On this basis, the parameters affecting the seismic behavior of UHPC-NC composite columns reinforced by high-strength steel bars were analyzed, i.e., the axial compression ratio, the diameter and strength of longitudinal bar, the stirrup spacing, and the UHPC height. The results showed that, the displacement ductility coefficient of the composite column decreases with the increase of axial compression ratio, longitudinal bar diameter, and stirrup spacing; while it first increases and then gradually keep flat with the increase of longitudinal bar strength and UHPC height. The appropriate replacement height of UHPC can give full play to the material characteristics of high-strength reinforcement and UHPC, thus achieving good economy.

Abstract:A series of GDS dynamic triaxial tests under cyclic loading were carried out on the remolded loess in Haibei area in this paper. The effects of different cyclic dynamic stress and different loading frequencies on the cumulative plastic strain and stiffness degradation characteristics of the loess were studied, and the degradation model proposed by Idriss was also used in the tests. The test results show that under the same vibration times, both the cyclic dynamic stress and loading frequency have effects on the cumulative plastic strain and stiffness degradation index of the loess. Under large cyclic dynamic stress and low loading frequency, the cumulative plastic strain and the attenuation degree of degradation index of the sample are large. The degradation index decreases with the increase of cumulative plastic strain, and the attenuation degree is relatively slow under large cyclic dynamic stress and low loading frequency. The stiffness degradation index δ in double logarithmic coordinates is approximately linear with the loading vibration N, and the stiffness degradation model δ=N^-d can fit the test curve well. The correlation coefficient R² is greater than 0.9, indicating the fitting effect is good. The degradation parameter d increases with the increase of cyclic dynamic stress, and decreases with the increase of loading frequency.

Abstract:To study the local seismic performance of deep foundation pit supporting pressure structure of high-rise buildings under the action of ground motion acceleration during earthquake, a series of shaking table tests were carried out on the deep foundation pit project of a high-rise building by using the finite element software. A finite element calculation model of the deep foundation pit supporting pressure structure was first constructed. Then the ground motion accelerations of 0.4g, 0.5g, and 0.6g were input to test the seismic performance of the deep foundation pit supporting pressure structure with different insertion ratios at different construction stages, and the influence of different earthquake intensities on the displacement of the structure was also studied. Finally, through the mode decomposition response spectrum method, the displacement and acceleration response of the supporting pressure structure were obtained, and the test on the local seismic performance of the structure was realized. The test results showed that the seismic stability of deep foundation pit supporting pressure structure of high-rise buildings is related to the excavation depth, insertion ratio, and seismic intensity. The seismic stability of the supporting structure is inversely proportional to the excavation depth of deep foundation pit and seismic intensity, while it is directly proportional to the insertion ratio. The insertion ratio can effectively improve the seismic performance of deep foundation pit supporting pressure structure of high-rise buildings.

Abstract:Ground motions containing big velocity pulse, which are significantly different from ordinary ground motions, have a special destructive effect on building structures. Scientific prediction of the occurrence of big velocity pulse and analysis of factors affecting the occurrence of big velocity pulse play an important role in probabilistic seismic risk analysis and reduction of earthquake disasters. In this paper, 315 strong motion records were selected from the NGA database of the United States, and 289 records were obtained after preprocessing. Based on the processed strong motion records, the effects of different factors on big velocity pulse were studied with the relative frequency analysis method. Then the L1 regularized logistic regression method was used to establish a prediction model of big velocity pulse, and the AUC (area under curve) value of the model is 0.76. It was found that the model was the most sensitive to the distance of fracture zone through a sensitivity analysis of the influencing factors. Finally, the prediction model was verified by 35 items of Wenchuan earthquake data, and the results indicated that 30 earthquake records were predicted correctly. The results showed that compared with the existing models, the big velocity pulse prediction model proposed in this paper has better accuracy and reliability.

Abstract:The influence of structural parameters of seat abutment of small and medium span bridges on their seismic performance was studied by the pushover analysis method. The orthogonal numerical simulation test of four factors and three levels was carried out by selecting the stirrup spacing of abutment backwall, the horizontal bar spacing of abutment cap, the thickness of backwall, and the action height of main beam as the test factors. The peak displacement, peak load, average stiffness, and displacement ductility coefficient of the abutment were selected as the objective function to reflect the seismic performance. Through range analysis, the sensitivity of each parameter to seismic performance indexes of the abutment was obtained. The results showed that the thickness of backwall has the greatest influence on the peak load and average stiffness of abutment. With the increase of backwall thickness, the peak load and average stiffness increase by 29.8% and 33.4%, respectively. The action height of main beam and the stirrup spacing of backwall have a great impact on the peak displacement and displacement ductility of abutment. With the increase of action height of main beam and stirrup spacing of backwall, the variation of abutment peak displacement is not more than 9.2% and 11%, and the variation of abutment displacement ductility coefficient is not more than 10% and 6.7%.

Abstract:The reinforced concrete frame structure is easy to collapse under the action of earthquake due to the stress concentration and small lateral stiffness at the joints of structure,and the plastic hinges at the beam and column ends are seriously damaged and difficult to repair.A new structural form and a new type of artificial hinge were proposed in this paper.The self-adaptive structure can change the stiffness of the building structure and increase the natural period under earthquake,thus weakening the seismic action on the structure.The new artificial hinge with good resilience performance can solve the problem that the traditional plastic hinges are difficult to repair after failure.By setting the proposed artificial hinge,the beam end hinge was transferred from the beam root,thus the problem of stress concentration at the joints can be solved.The position of artificial hinge was changed by the ABAQUS software,and three finite element models for the adaptive structure were established and compared with the cast-in-situ frame model.The results showed that the adaptive structure-based control system reduces the seismic action of the structure by 70%,and the seismic performance and resilience performance of artificial hinges and joints are good.The adaptive structure can be widely used in various prefabricated buildings.It can greatly reduce labor costs and completely realize the intelligent construction of prefabricated buildings.In addition,a more convenient calculation method of bearing capacity and design suggestions for setting artificial hinges were put forward.

Abstract:A 3D numerical model for simulating the dynamic response of high-piled wharf in liquefaction ground was established and then used in the centrifuge shaking table test. On this basis, the influence of some parameters on the reinforcement effect of high-piled wharf in liquefaction ground were systematically studied, i.e., the distance between the reinforcement area and the wharf, the diameter and length of the stone column. Then, the deformation and stress law of high-piled wharf in liquefaction ground under different reinforcement parameters were revealed. The results showed that the seismic performance of high-piled wharf in liquefaction ground is positively correlated with these parameters; the stone column with large diameter and long size can effectively control the horizontal displacement and bending moment of high-piled wharf during earthquake. The research results of this paper are of great significance for the reinforcement of high-pile wharf foundation in liquefaction ground.

Abstract:Power tower, a kind of structure with energy supply capacity, is an important part of lifeline project, so its post-disaster evaluation is of great significance. However, because of the interference of surrounding buildings, exposed rock mass, and riverbed, the recognition accuracy of the power tower is low. Therefore, this paper proposed a new spatial reasoning method based on spatial features, which can identify electric towers with high accuracy. The proposed method was verified by taking the wind power base in the desert of northwest Gansu Province as an example, in which the power tower accounts for the majority. Through experimental calculation, the recognition accuracy of this method reaches 98.96%, 14.66% higher than that of the traditional method. Furthermore, to evaluate the effect of this method, the evaluation index of mis-distance risk was proposed to determine the offset between the recognition result and the actual structure. Calculation result indicated that the probability of low risk by using this method is 94.21%. The proposed method can provide basic data and technical support for the disaster assessment of power tower after the disaster.

Abstract:The Menyuan M6.9 earthquake occurred on January 8, 2022, induced many kinds of co-seismic geo-hazards, i.e., collapses, landslides, sand liquefaction, and ground fissures. Based on the field investigation results, the distribution and characteristics of various types of geological disasters induced by the M6.9 earthquake were obtained in this paper. Besides, the reasons for the undeveloped seismic geo-hazards were analyzed, and the long-term effects of seismic geo-hazards were predicted. The results showed that the geo-hazards induced by the M6.9 earthquake are mainly distributed near the epicenter. The collapses and rockfalls are not big. Most of the landslides are rock landslides, which are dominated by the sliding of moraine and surface rock and soil. Due to the freezing of surface soil and the dissipation of pore water pressure, the liquefaction of saturated sand is beaded along narrow ground fissures, and the ejecta is mostly silty and fine sand. Four sinistral oblique surface rapture zones and a large number of ground fissures are formed in the meizoseismal area. The barrier effect of fault fracture zone on strong motion, thin overburden layer, and freezing of surface soil may cause the undevelopment of seismic geo-hazards. A large number of ground fissures generated by the earthquake weaken the stability of slopes and accumulation bodies, which may induce landslides under the coupling action of concentrated rainfall and freezing-thawing cycles. In addition, loose deposits in gully beds generated by collapses and landslides may increase the risk of debris flow in earthquake-affected areas.

Abstract:On January 8, 2022, an M_S6.9 earthquake occurred in Menyuan County, Qinghai Province. In this paper, the seismic data of 14 869 events in Menyuan and its surrounding areas (36°-39°N, 101°-104°E) observed by regional digital stations in Qinghai and Gansu from January 1, 2009 to February 8, 2022 were relocated by using the double difference tomography (Tomodd) method. The results showed that the focal depth of earthquakes in Menyuan and its surrounding areas are mainly concentrated in a depth range of 5-15 km, especially at near 10-km depth. It is inferred that this depth area is the main seismogenic area in the study area. Based on the seismic relocation results and the three-dimensional velocity structure of the mainshock area, the seismogenic mechanisms of the 2016 Menyuan M_S6.4 earthquake and the 2022 Menyuan M_S6.9 earthquake were analyzed and compared. It is found that two earthquakes are both located at the edge of high-velocity anomaly block, and the velocity structure corresponds well to local fault and two earthquake sequences. The 2022 Menyuan M_S6.9 earthquake, located at the western tip of the high-velocity body, is a strike-slip earthquake caused by the sliding of the high-velocity body due to the clockwise stress on the northeast edge of the Qinghai-Tibet Plateau.

Abstract:At 1: 45 on January 8, 2022, an earthquake of magnitude 6.9 occurred in Menyuan County, Qinghai Province. The coseismic displacement field obtained from GNSS continuous observation data near the epicenter showed that the coseismic displacement of QHME station, which is closest to the epicenter, was the largest, reaching 20.31 mm in the east-west direction and -35.45 mm in the north-south direction. The coseismic displacements of five stations near the epicenter reflected the characteristics of left-lateral coseismic rupture of the earthquake. The results of regional strain time series and baseline time series between GNSS stations showed that the crustal movement in the north section of Lenglongling fault is stronger than that in the south section, which corresponds to the area where the earthquake occurred. The results of dynamic GNSS strain field before the earthquake showed that the shear strain value in the study area was small, with a slight decreasing trend, but it was always at the edge of the high strain zone. The slip velocity of the seismogenic fault changed little, and the value first increased and then weakened. The degree of fault blocking increased before the earthquake, which may lead to the occurrence of the earthquake.

Abstract:An M6.9 earthquake occurred in Menyuan County, Qinghai Province on January 8, 2022. There were anomalies of radon in the escape gas in Xining and Ledu of Qinghai Province before the earthquake. This paper focused on the abnormal characteristics by using the fluid geochemical method. The results showed that the total dissolved solids (TDS) of sampling point in Xining ranged from 9 084.3 to 11 316 mg/L, and that in Ledu ranged from 897.01 to 989.26 mg/L. The hydrochemical types are Na-SO₄ and Na-Cl, showing that the degree of water-rock reaction is weak. The concentration of SO^2-₄ and HCO^-₃ changed significantly, indicating that low mineralized water with short groundwater runoff was mixed before and during the anomalies. The calculation results of heat storage temperature and circulation depth showed that the exchange of deep water body was not obvious. During the preparation of an earthquake, the regional stress loading leads to the formation of cracks and pores in surrounding rocks, resulting in the change of radon value in the geophysical field. The water-rock reaction increases in the same period, resulting in the corresponding change of hydrochemical ion concentration. Combined with the abnormal mechanism of radon value and the study of historical earthquake events, the anomalies are suggested to be credible earthquake precursor anomalies, which have a good indicating significance for M≥6 earthquakes in the Qilian seismic belt.

Abstract:Based on a comprehensive analysis of the characteristics of radon anomalies in Jiayuguan before seven M_S≥6.0 earthquakes in Qilian earthquake area and its surrounding areas since 1991, the relationship between the trend anomaly of gas radon in Jiayuguan and the Menyuan M_S6.9 earthquake was further analyzed. The results showed: (1) The concentration of gas radon appeared obvious response to some earthquakes and had no response to other earthquakes in the study area. There is no obvious relationship between the gas radon response and the epicenter distance. (2) Whether the gas radon is abnormal is closely related to the seismogenic fault of earthquake. The anomalies of gas radon have similar characteristics before earthquakes with the same seismogenic fault. The gas radon concentration appeared distortion anomalies in annual variation and sudden jump in short term before eathequakes distributed along the Dachaidan-Zongwushan fault and had no anomalies before eathequakes distributed along the Tuolaishan-Lenglongling fault. (3) The trend anomaly of gas radon in Jiayuguan may be related to the enhancement of tectonic activity in the study area, which may be the response of Maduo M_S7.4 and a series of M_S5.5 earthquakes occurred in the Qilian Mountains and its surrounding areas, including the Menyuan M_S6.9 earthquake. This study is of great significance to the judgment of earthquake precursory anomalies and the improvement of earthquake tracking monitoring and prediction efficiency.

Abstract:Based on the brightness temperature data obtained from Chinese geostationary meteorological satellite, this paper studied the thermal radiation anomalies before the Menyuan M6.9 earthquake on January 8, 2022 by using the wavelet transform and the relative change of power spectrum, and made a retrospective study on the thermal radiation anomalies of previous earthquakes in the middle-eastern Qilian seismic belt. The development process of thermal radiation anomaly of the Menyuan M6.9 earthquake can be divided into three stages: initial evolution stage, strengthening and persisting stage, weakening and disappearing stage. The largest area of intense radiation was about 80 000 km², and the earthquake occurred in the northwest of the region. The peak value of the relative power spectrum was 17 times the average value, and the M6.9 earthquake occurred 82 days after the peak value. The significant feature of the anomaly is the large area and long duration of high intensity thermal radiation. The characteristics of thermal radiation anomalies before several earthquakes in the middle-eastern Qilian seismic belt can accumulate experience for the judgment of earthquake situation in this area.

Abstract:The continuous waveform data three days before and seven days after the M_S6.9 earthquake in Menyuan, Qinghai Province on January 8, 2022 were recorded by the permanent stations of Gansu seismic network and the shared stations of neighboring provinces. In this paper, the aftershock sequence was detected by the automatic cataloging program based on the data, and the results were compared with the manual cataloging results. It was found that the results of automatic catalogue and manual catalogue are basically the same; the average epicenter position difference is within 5 km, and the magnitude difference is between M_L-0.2~M_L0.2. The earthquake occurrence time from automatic catalogue results is slightly earlier than that from manual catalogue,but the difference of the occurrence time of most aftershocks in the two catalogs is within 2 s. The output speed of automatic cataloging is fast, so it could detect small aftershocks that cannot be recognized manually, thus improving the completeness of the catalogue. On the whole, the output results of the automatic cataloging system can meet the expected objectives, and can provide data support for relevant scientific research, such as earthquake swarm trend judgment and rapid inversion of rupture process.

Abstract:An M_S6.9 earthquake occurred in Menyuan County, Qinghai Province on January 8, 2022. Based on the observation data of the electric field within 300 km of the epicenter in recent 5 years, 9 observation stations were analyzed and selected. According to the seepage (movement) model of rock fissure water (charge), the dominant azimuth of the geoelectric field was calculated. The loading and unloading response ratio (LURR) value of the geoelectric field was calculated through the LURR calculation method of Coulomb stress-triggered model. The results showed that: (1) The stations with geoelectric field anomalies calculated by the two different methods are consistent in spatial distribution. Among them, the dominant azimuth and LURR of the geoelectric field at Gufeng, Huangyangchuan, Sitan, and Lanzhou stations showed abnormal changes before the earthquake, while those at Shandan and other stations did not show obvious anomalies. (2) The time series changes of Lanzhou and Sitan stations using the two calculation methods are consistent, showing quasi synchronization. Combined with the focal mechanism solution, the correlation between the dominant azimuth of abnormal stations and the principal compressive stress P-axis direction was analyzed, and the results basically conform to the petrophysics theory. The two calculation methods of geoelectric field dominant azimuth and LURR value are related in mechanism, and a comprehensive analysis of their abnormal evolution characteristics may help to further understand the physical process of earthquake preparation.

Abstract:Combined with the seismicity anomalies in 2021, this study systematically summarized the temporal-spatial characteristics of the seismic quiescence broken of M5 earthquakes in the Qilian Mountain seismic zone and M_L3.6 earthquakes in the middle-eastern section of Qilian Mountain seismic zone before the Menyuan M_S6.9 earthquake in 2022. The results showed that the seismic quiescence of M5 earthquakes in the Qilian Mountain seismic zone has indicative significance for the occurrence of M≥6 earthquakes in local and surrounding areas; the seismic quiescence of M_L3.6 earthquakes in the middle-eastern section of Qilian Mountain seismic zone has indicative significance for the occurrence of M≥5 earthquakes. The break of quiescence zone indicates that the occurrence urgency of moderate and strong earthquakes increases, and the earthquake usually occurs one year after seismic quiescence break. This paper summarizes the prediction significance of two indexes in detail, and makes a systematic prediction efficiency evaluation, which can provide reference experience for the judgment of the risk of subsequent strong earthquakes.

Abstract:The rapid assessment product of earthquake intensity is an important basis for judging the disaster situation during the " black box period" of emergency response after a destructive earthquake. Based on the aftershock sequence within 2 h after the M6.9 earthquake in Menyuan, Qinghai Province, we used a ground motion attenuation model with the shortest fault distance to rapidly evaluate the earthquake intensity in this paper. The results showed that the intensity distribution obtained by using the aftershock sequence within 30 minutes after the M6.9 mainshock can preliminarily determine the hardest stricken area and the disaster areas, but the scope of disaster areas is smaller than the actual survey result. The intensity distribution obtained by using the aftershock sequence within 1.5 h is consistent with the field investigation results, and the calculation results using the aftershock sequence within 2 h have no obvious change. The seismic intensities obtained using the relocated aftershock sequence are more accurate than those obtained from the conventional aftershock sequence, but a suitable relocated method needs to be selected. In this earthquake, the intensity range evaluated by using the aftershock sequences shows a characteristic that the accuracy is higher with growing intensity, and the hardest-hit areas determined using the result are accurate. The proposed method enriches the existing system of rapid intensity assessment, but its applicability and conditions need to be further studied.

Abstract:On 8 January, 2022, an earthquake (M_S6.9) occurred in Menyuan County, Qinghai Province. The epicenter was located at the junction of the western end of the Lenglongling fault and the Tuolaishan fault. After the earthquake, we used the high-resolution GF-7 satellite images to interpret the seismic surface ruptures produced by the earthquake in detail. The results were then compared with the field investigation results, and the distribution and combination characteristics of the surface ruptures were obtained. The results showed that two surface ruptures with a length of about 21 km and 5 km are formed during the earthquake. They are distributed along the western segment of Lenglongling fault and the eastern segment of Tuolaishan fault, respectively. The surface ruptures are composed of a series of en-echelon seismic fractures, compression mole tracks, and tension depressions, showing obvious left-lateral strike-slip characteristics. Unfortunately, quantitative data such as coseismic offsets were not recognized by satellite images. Furthermore, the historical surface ruptures in the eastern segment of the Lenglongling fault were compared and the seismic risk of the Lenglongling fault in future was also discussed.

Abstract:This paper studied the deformation field and seismogenic structure of the Menyuan M_S6.9 earthquake in Qinghai Province on January 8, 2022, by using the ascending and descending Sentinel-1A data and the differential interferometric synthetic radar (D-InSAR) technique. The source parameters were then inverted to determine the fault geometry parameters and the non-uniform fault slip distribution with a dislocation model in an elastic half-space. The results showed that the coseismic deformation field of Menyuan earthquake is distributed along the NWW-SEE direction. The maximum surface deformation of the ascending and descending images on the southern edge of the fault zone are 61 cm and 62 cm, respectively; the maximum surface deformation of the ascending and descending images on the northern edge of the fault zone are 43 cm and 56 cm, respectively. The fault scale model of InSAR coseismic deformation field is 30 km long and 18 km wide, with the maximum slip of 3.5 m. Combined with the movement characteristics and geometric characteristics of Lenglongling fault, it is determined to be the seismogenic fault of Menyuan M_S6.9 earthquake.

Abstract:An M_S6.9 earthquake occurred in Menyuan County, Qinghai Province, on January 8th, 2022. The epicenter is located at the tectonic transform region of the Lenglongling fault and Tuoleshan fault along the Qilian-Haiyuan fault zone (37.77°N, 101.26°E) of the northeastern Tibetan Plateau. This paper introduced the typical earthquake disasters and characteristics of co-seismic surface ruptures. The results of field investigation after the earthquake showed that the main shock ruptured two obvious surface zones with the length up to 26 km, and the overall strike was directed along NWW. The rupture property is mainly sinistral strike-slip with thrusting slip by dipping to NE. The typical rupture landforms caused by fault dislocation mainly exhibit as en echelon combined of separation fractures, tension shear fractures, seismic bulges, and fault scarps. The surface rupture at the segment from Daohe to Liuhuanggou is the strongest, with large scale and good continuity, causing the most significant earthquake damage, and the scale of the surface rupture gradually decreases to the east and west ends. The main shock ruptured the ice surface of the Daohe and the Liuhuanggou, with typical deformation of a series of fractures and bulges as well as small scale of geological disasters, such as slope collapse and rolling stones formed along the river bank. Based on the comprehensive analysis of post-earthquake damage and surface rupture distribution, the region between Liuhuanggou and Daohe can be determined as the macro epicenter of the Menyuan M_S6.9 earthquake.

Abstract:After the Menyuan M_S 6.9 earthquake occurred on January 8, 2022, the aftershock catalogue contains a large number of single-station events. To solve the inaccuracy of single-station event location, this paper used the source location method of coda wave interference (CWI) to relocate 101 single-station events recorded by Menyuan station within 8 hours after the mainshock. First, we calculated the interval uncertainty matrix of the coda wave part of the event pair, so as to estimate the interval between the seismic event pairs with similar focal mechanism in the cluster. Then, we solved the relative position of a group of events in the cluster by optimizing the interval. Finally, the relocation results were evaluated and found to be relatively reliable.

Abstract:Accurate detection and location of microseismic events in the moderate-strong earthquake sequence is of great significance to determine the seismogenic structure. On January 8, 2022, an M_S 6.9 earthquake occurred in Menyuan County of Qinghai Province, which is located at the northeastern margin of the Tibet Plateau. To investigate the seismogenic fault of this earthquake, we first used the double difference location method to relocate the catalogue events from China Earthquake Network Center (CENC), which includes 1 010 earthquakes from January 8 to January 16, 2022, and then obtained the precise location of 404 earthquakes. The original seismic catalogue (CENC) and double difference relocation catalogue (HypoDD) were then used to detect micro-earthquakes from the continuous waveform data of 9 stations within 150 km of the source region. The results showed that the number of aftershocks identified based on CENC catalogue is 3.0 times more than that of the original catalogue, and the number of aftershocks identified based on HypoDD catalogue is 2.1 times more than that of the original catalogue and 5.8 times more than that of the HypoDD catalogue. The micro-earthquake detection of the two earthquake catalogues reduced the completeness of M_L from 1.7 to 1.1. The spatial location of the new earthquake catalogue showed that, the aftershocks mainly spread westward along the Tuolaishan fault. And eight minutes after the mainshock, both the Tuolaishan fault and the Lenglongling fault ruptured. Based on the high resolution earthquake locations and the focal mechanism solution, we suggested that the initial rupture of the 2022 Menyuan M_S 6.9 earthquake is located in the nearly EW-trending Tuolaishan fault. The occurrence of the earthquake is mainly due to the long-term extrusion of the Indian plate in the northeastern direction.

Abstract:In this paper, the correlation coefficient of surface strain, the principal strain, and the principal azimuth were calculated and projected by using the borehole strain data from Gansu-Qinghai geophysical network from January 2021 to January 2022. The correlation coefficient of surface strain and the data precision were used for data quality control. On this basis, the spatial distribution and temporal variation characteristics of borehole strain in Gansu-Qinghai area were analyzed. The results showed that the changes of principal strain, principal azimuth, and map projection in 2021 can clearly reflect the tectonic movement in the study area. The coseismic changes of the principal azimuth and maximum principal strain projection are consistent with the changes of surface coseismic displacement field and strain field caused by the Menyuan M_S 6.9 earthquake on January 8, 2022. The above results can benefit the investigation of geological structure changes, and provide support for the seismic risk tracking and imminent earthquake prediction in the study area.