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Characteristics of Spatial and Temporal Distribution of Strong Earthquakes in Chinese Mainland and Trend after Maduo MS7.4 Earthquake WANG Peng, SHAO Zhi-gang, SHI Fu-qiang, YIN Xiao-fei EARTHQUAKE    2021, 41 (4): 1-14.   DOI: 10.12196/j.issn.1000-3274.2021.04.001 Abstract （544）      PDF（pc） （4092KB）（318）       Knowledge map    Analyzing characteristics of spatial and temporal distribution of strong earthquakes in Chinese mainland is benefit for determining trend of strong earthquakes in this region. Limited by completeness of catalogue, most analysis of strong earthquakes time intervals in Chinese mainland is on the basis of catalogue since 1900. Due to relative short duration of catalogue, it is difficult to exclude the possibility that current temporal characteristics of strong earthquakes are accidental, and it may cause over fitting which affects forecasting performance. To solve those problems, this paper analyzed synthetic catalogue based on the data from 2021—2030 key area for earthquake surveillance and protection in Chinese mainland. The results show that alternates clusters and quiescence is a common phenomenon for regional strong earthquakes. When supposed the active faults with quasi periodic recurrence behavior, temporal characteristics of synthetic catalogue are closest to the current catalogue. Based on understanding above, strong earthquake interval in Chinese mainland is fitted by the single parameter exponential distribution with wider application. Combined with structural correlation of adjacent strong earthquakes, trend of strong activity in Chinese mainland after the May 22, 2021 Maduo MS7.4 earthquake is analyzed. Results show that the next MS≥7.0 magnitude in Chinese mainland is likely to happen in next two years, the probability being 61.81% before the end of 2022. The probability with the next strong earthquake will occur in 2021 is 30.58%, and the most likely area is Bayankala block; The probability of the next strong earthquake within 2022 is 44.97%, and the middle-south section of the North-South seismic belt should be noticed.

Textual Research and Causative Structure of the Northern Xunwu Earthquake in Jiangxi Province on September 21, 1941 DENG Hui, DONG Fei-fei, XIE Bin EARTHQUAKE    2021, 41 (3): 104-113.   DOI: 10.12196/j.issn.1000-3274.2021.03.008 Abstract （470）      PDF（pc） （2684KB）（168）       Knowledge map    The epicentre location and isoseismic line of the 1941 M5¾ northern Xunwu earthquake in jiangxi province are not consistent in the seismic catalogue and investigation report of each version. On the basis of absorbing previous research results and supplementing new data, through detailed textual research of seismic survey data, we check the seismic intensity of each recorded point, review macro epicentre parameters of the earthquake, and redetermine its isoseismal range. Combined with the seismogeological investigation, the possible seismogenic structures of the 1941 AD northern Xunwu earthquake are studied comprehensively. According to the comprehensive analysis, the macroscopic epicentric parameters of the 1941 M5¾ northern Xunwu earthquake are 25.1°N and 115.7°E, and its isoseismal lines are distributed in the NW direction. Its seismogenic structure may be the huanggang-bijiashan fault, and its controlling structure may be the heyuan-shaowu fault.

Geometric Distribution of Huaihe—Nvshan Lake Section of Anqiu—Juxian Fault in the Middle Part of Tanlu Fault Zone YANG Yuan-yuan, LI Peng-fei, FANG Liang-hao, LU Shuo, YAO Da-quan, ZHAO Peng, ZHENG Hai-gang, SHU Peng, ZHENG Ying-ping, PAN Hao-bo EARTHQUAKE    2022, 42 (1): 54-69.   DOI: 10.12196/j.issn.1000-3274.2022.01.004 Abstract （450）      PDF（pc） （9815KB）（71）       Knowledge map    The latest active Anqiu—Juxian fault named F5 fault in the middle section of the Tanlu fault zone is an important seismically active fault in the eastern China. The present studies have shown that the F5 fault has extended southward into the Huaihe—Nvshan Lake in Anhui province, however, the specific geometrical distribution of this segment still has two major unresolved problems. Firstly, does the eastern fault of the Ziyang mountain belongs to the branch of F5 fault? secondly, does the F5 fault extend south to the northern shore of Nvshan Lake? In order to solve these problems, based on the methods of remote sensing interpretation, geomorphological survey, trench excavation and dating of faulted strata, we conducted research on the faults on the eastern side of Ziyang mountain and the faults along the northern shore of Nvshan Lake. The results show that the eastern fault of the Ziyang mountain developed at an older age, and experienced a strong thrust compression movement in the early and middle Pleistocene. It did not active since the late Quaternary and does not belong to the F5 fault branch. The Tan-Lu fault zone faulted the Late Pleistocene stratum in the ShangZhan area on the northern shore of Nvshan Lake. The F5 fault has completely penetrated between the Huaihe River and Nvshan Lake, its trace is single and continuous, with a total length of about 20 km. It has been discussed that the F5 fault could terminated southward from Nvshan Lake to Mingguang City. The termination of the fault is controlled by the regional ancient structural pattern, which indicating that the fault is both new and inherited.

Application of Three Strain Calculation Methods Based on GNSS Data in the Southeastern Margin of Tibet Plateau JIN Yang, JIN Hong-lin, GAO Yuan, HUANG Xing EARTHQUAKE    2021, 41 (4): 57-67.   DOI: 10.12196/j.issn.1000-3274.2021.04.004 Abstract （294）      PDF（pc） （7350KB）（75）       Knowledge map    The methods of using the GNSS velocity field to solve the strain rate have multiple characteristics, which can be divided into mathematical methods and physical methods. This paper selects three mathematical methods to solve the strain rate: Least Squares Collocation Method, Multi-scale Spherical Wavelet Method, Gussian Weighted Interpolation Method, to resolve the GNSS velocity field and uniform GNSS velocity field on the southeastern margin of Tibet Plateau from 1999 to 2019 (97°E~106°E, 21°N~30°N), and the applicability characteristics of the above three methods in this area is discussed. By analyzing the results of principal strain rate (maximum/minimum), maximum shear strain rate, and surface strain rate obtained from two sets of different data distributions, we found that the strain parameters obtained by multi-scale spherical wavelet method have higher resolution in the southeastern margin of Tibet Plateau. In the high-density data distribution, the spatial deformation characteristics in a small area can be reflected in detail, which is helpful to determine the fault deformation characteristics. The result only represents the studied area on the southeastern margin of Tibet Plateau, and the selection of calculation methods for other areas still needs to consider the conditions of the structural deformation background and the distribution density of measurement points.

Basic Characteristics of Tectonics and Seismic Anisotropy in the Southeastern Margin of the Qinghai-Tibet Plateau LI Ying, GAO Yuan EARTHQUAKE    2021, 41 (4): 15-45.   DOI: 10.12196/j.issn.1000-3274.2021.04.002 Abstract （286）      PDF（pc） （6306KB）（242）       Knowledge map    The southeastern (SE) margin of the Qinghai-Tibet Plateau is jointly affected by the northeastward pushing of the Indian plate, the southeastward extrusion of the plateau material, and the blocking of the Sichuan Basin and South China Block, which has become a key channel of the southeastward escaping material of the Qinghai-Tibet Plateau. In this paper, we summarizes the results of seismic anisotropy of different depths obtained by different seismic phases and different methods in the SE margin of the Qinghai-Tibet Plateau. Combining the distribution of faults, surface movement, tectonic stress and deep structure in the region, we comprehensively analyzed the medium anisotropy and deformation coupling characteristics from the upper crust to the middle-to-lower crust and upper mantle. The difference in seismic anisotropy of the crust and the upper mantle in the SE margin of the Qinghai-Tibet Plateau reflects the complex deep structure as well as crust and upper mantle deformation in this region. As scientific issues such as the formation mechanism of the Qinghai-Tibet Plateau, the coupling state of crust and mantle and the distribution of weak layers are still under academic discussion, it is beneficial to obtain more accurate and detailed seismic anisotropy images of crust and upper mantle by effectively combining different data and synthesizing various methods, thereby providing more effective constraints on the research of deep material movement and dynamic model.

Application and Prospect of Artificial Intelligence Real-time Seismic Monitoring and Analysis System at the China Seismic Experimental Site ZHOU Lian-qing, ZHAO Cui-ping, ZHANG Jie, CHE Shi EARTHQUAKE    2021, 41 (3): 1-21.   DOI: 10.12196/j.issn.1000-3274.2021.03.001 Abstract （279）      PDF（pc） （10027KB）（104）       Knowledge map    The “Artificial Intelligence Earthquake Monitoring” (EarthX) system is currently the only real-time artificial intelligence seismic monitoring system in the world. Since December 2018, the EarthX system has been trial-operated at the China Seismic Experimental Site to process earthquakes recorded by 123 seismic stations in Sichuan and Yunnan in real time. The focal location and magnitude of the earthquakes are quickly shown within a few seconds after the first P waveform of the stations are received, and the EarthX system only takes about 28.9 seconds to locate an earthquake. The focal mechanism solution and moment magnitude of the earthquakes are quickly produced in about 1 to 3 minutes without any manual intervention. During the period from January 1, 2020 to August 4, 2020, the EarthX system recorded a total of 897 earthquakes and produced 81 focal mechanism solutions for earthquakes above M3.0. The automatic locating of earthquakes of magnitude 3 and above and the automatic output of focal mechanism solutions are basically realized in the system and the focal mechanism solutions are produced in average 103.8 seconds after the earthquake occurrence. The EarthX system solves the problem of producing earthquake focal mechanism solutions accurately in a short time. Through the popularization and application of the EarthX system, it can gradually replace the traditional seismic monitoring system, and liberate the seismic analysts from heavy seismic data processing work.

Earthquake Focal Mechanism Solutions and Spatio-temporal Variations of Tectonic Stress Field in Xinfengjiang Reservoir since 2012 JIANG Xi-jiao, LIN Qing-xi, GONG Xuan, YANG Xuan EARTHQUAKE    2022, 42 (3): 64-80.   DOI: 10.12196/j.issn.1000-3274.2022.03.005 Abstract （276）      PDF（pc） （5194KB）（69）       Knowledge map    The seismic activity and the distribution of focal mechanism and tectonic stress filed are of great significance for understanding the characteristics and genetic mechanism of induced earthquakes in the Xinfengjiang reservoir. Based on 142 seismic events (ML≥2.0, 2012—2018), we calculated the focal mechanism solutions with FOCMEC method and invert the regional stress field with SATSI method. Then, we discussed the spatio-temporal variation of the tectonic stress field in Xinfengjiang reservoir. The results show that the earthquake rupture type in Xinfengjiang reservoir is mainly normal-faulting type with partial dip-slip components, and the second is strike-slip type. The advantageous directions of P-axis are NWW—SEE, and the plunge is close to vertical; the advantageous directions of T-axis are NNE—SSW, and the plunge is close to horizontal. The entire reservoir is mainly under action of the vertical extrusion of NWW—SEE and the horizontal stretching of NNE—SSW, and the stress is of normal-faulting type. From the NW—SE direction in the southeast to the NWW—SEE direction in the northwest, the maximum principal stress axis shows a counterclockwise rotation, with the rotation angle of about 18°, and the type of stress filed is changed from normal-faulting to strike-slip. Since 2012, the stress field of various regions in Xinfengjiang reservoir has been in a relatively stable state, but relatively large changes may occur in 2015 and 2018. Whether there is any variations of maximum principal stress axis in the studied region is unknown according to present calculation results, which need to be further verified.

Study on Creep Evidence and Deep Deformation Mechanism of the Chafangkou Segment of the Northern Piedmont Fault of Xizhoushan YAN Xiao-bing, LI Wen-qiao, YOU Wen-zhi, SUN Hai-yan, HAO Xue-jing, LI Hong-wei EARTHQUAKE    2023, 43 (3): 91-101.   DOI: 10.12196/j.issn.1000-3274.2023.03.007 Abstract （218）      PDF（pc） （2951KB）（84）       Knowledge map    According to historical records, in 1038, an M71/2 earthquake occurred in Xinzhou and Dingxiang County. Previous studies have shown that the seismogenic structure of this earthquake is the northern piedmont of Xizhoushan Fault, the epicenter of which is located near Chafangkou, Dongcun town, Dingxiang County. The leveling of the Chafangkou segment of the northern piedmont fault of Xizhoushan fault began in 1985, and the two plates of the fault moved at a total of 9.09 mm to 2021, with an average annual creep slip of 0.25 mm. The trend of creep deformation shows that there is creep movement in the segment of Chafangkou every year, but the overall creep rate is low. The content of clay in the seismic fault sumple of Chafangkou is 23% by using the method of X-ray diffraction, the clay content of fault breccia near the fault is 8%, and the total clay mineral content decreases gradually from old fault mud to fault breccia. The study shows that the clay content is the key factor to determine whether the fault is creeping or not. The natural fault of the northern piedmont of Xizhoushan fault is simulated in the confining pressure environment of 5 km underground (about 130 MPa), and high temperature and high pressure experiments were carried out at a constant disturbing pressure of 100 MPa. The results show that the natural faults in the northern piedmont of Xizhoushan fault exhibit steady creep slip at the temperature of 25℃, 50℃, 100℃ and 150℃ and the disturbing velocity of 0.122 μm/s and 1.22 μm/s。

Hydrogeochemical Characteristics of Hot Springs in Nantinghe Fault Zone, Yunnan Province WANG Wan-li, ZHOU Xiao-cheng, SHI Hong-yu, YAN Yu-cong, OUYANG Shu-pei, LIU Feng-li, FANG Wen-ya, LI Peng-fei EARTHQUAKE    2022, 42 (2): 14-32.   DOI: 10.12196/j.issn.1000-3274.2022.02.002 Abstract （217）      PDF（pc） （5701KB）（107）       Knowledge map    The activities of fault zones may be monitored well by hydrogeochemical methods. From July 2015 to November 2019, concentrations of dissolved species including the major, trace elements and stable isotopes in 194 water samples collected from 12 thermal springs of Nantinghe fault zone were used to characterise their hydrogeochemical feature and to reveal the relationships between water chemistry and regional tectonic activity. And Xingfu hot spring was continuously monitored from February 2019 and water samples were collected every three days. The results show that ① The stable isotope data (δD, δ18O) suggesting that the water of hot springs are rechanged by circulation of meteoric waters, where the east and west branch fault recharge elevation ranges are 1.6~2.1 km and 1.0~1.9 km; ② There are four main types of water chemistry in the study area: HCO3-Na、 HCO3·SO4-Na、 SO4-Ca、 HCO3-Ca. The east branch fault zone is HCO3-Na type water. There are HCO3·CO4-Na and HCO3-Na in the northeastern segment of the west branch, HCO3-Na water in the middle section, and HCO3-Ca water in the southwestern segment; ③ SiO2 in the region is 11.1~101.0 mg/L, and aqueous geothermometry suggests that thermal storage temperature is 42.7℃~137.8℃. This data, along with estimated temperature, gave an estimated circulation depth for the spring waters of 0.6~2.5 km. Maolan and Xiaodingxi in the northeastern segment of the west branch are partially balanced water, while the eastern branch and other hot springs are immature water with low salinity. The comprehensive enrichment factors and contents of trace elements reflect that the water-rock reaction degree is weak in the internal circulation of the fault; ④ There is a certain correlation between chemical changes of hot spring water and seismic activity. Five days before the Yongde MS4.4 earthquake, the Cl- content increased by about 40.6% compared with the background value and the epicentral distance is 77 km. one day before Lincang ML3.3 earthquake, the SO2-4 content increased by about 27.2% compared with the background value and the epicentral distance is 13 km. The dissolved Cl- and SO2- 4in Xingfu hot spring were obviously abnormal to the seismic precursor of near-field earthquake. In a word, it is a great significance to judge and recognize the short-term and impending precursory anomalies of earthquakes with the study of the hydrogeochemical characteristics of the hot spring in NTHF (Nantinghe Fault).

Preliminary Analysis of GPS Strain Field Cloud Method for Idenetifying Seismic Deformation Field Anomalies CHANG Jin-long, GAN Wei-jun, MENG Ling-sheng, ZHU Cheng-lin, LIU Jun-qing EARTHQUAKE    2021, 41 (3): 22-31.   DOI: 10.12196/j.issn.1000-3274.2021.03.002 Abstract （213）      PDF（pc） （4357KB）（166）       Knowledge map    This paper introduces a method to obtain the anomaly of seismic deformation field by strain field cloud map. The basic idea is as follows. Firstly, we fit the GPS displacement time series in the specified time window, interpolate the velocity field and calculate the strain field. Then we obtain the cloud map of the strain field which varies continuously in space-time sliding with a certain step length and extract the anomaly information of seismic deformation field. We analyzed the relationship between strain field cloud map and Menyuan MS6.4 earthquake. The results show that this method has certain indicative effect on earthquake. At the 2019 year-end provincial Seismologic Consideration, the practicability of this method is tested by predicting Nenjiang ML4.5 earthquake. The research shows that this method is an effective and intuitive method to identify abnormal deformation field before earthquake.

Effect of the Earth Model on the Calculation of Seasonal Load Deformation: A Case Study of the Sichuan—Yunnan Area SHE Ya-wen, WU Wei-wei, LIU Tai, FU Guang-yu EARTHQUAKE    2021, 41 (4): 46-56.   DOI: 10.12196/j.issn.1000-3274.2021.04.003 Abstract （209）      PDF（pc） （5866KB）（178）       Knowledge map    This study uses GNSS and GRACE data of the Sichuan-Yunnan area, combined with different Earth models and surface Load theory, to study the effect of the Earth model on the calculation of seasonal surface load deformation. This study has reference value for selecting a suitable Earth model to carry out research in surface load deformation. The research shows: ① The amplitude of the crustal vertical seasonal deformation observed by GNSS at the Sichuan-Yunnan area is about 20 mm. The vertical deformation deduced by GRACE data is consistent in phase with the results of GNSS, but different in amplitudes. ② The load Love numbers of the regional Earth model are quite different from other Earth models, and the load Love number hn is more sensitive to the change of the Earth’s structure. ③ The regional Earth model can improve the surface load deformation results of GRACE inversion, thereby reducing the difference with GNSS observation results. ④ The reductions of weighted root mean square corresponding to the most GNSS stations at the Sichuan-Yunnan area show a trend of increasing gradually from northeast to southwest.

Typical Underground Fluid Anomalies of the Wuwei, Anhui ML4.1 Earthquake Occurred in 2018 MIAO A-li, LI Feng, WANG Jun, ZHU Tao, YE Bi-wen EARTHQUAKE    2021, 41 (4): 192-202.   DOI: 10.12196/j.issn.1000-3274.2021.04.015 Abstract （196）      PDF（pc） （2058KB）（150）       Knowledge map    This paper analyzed the typical underground fluid anomalies and the focal mechanism of Wuwei ML4.1 earthquake occurred on April 6th, 2018. The results show that the anomalies appeared before the 2018 Wuwei earthquake scattered in the range of 64~233 km. According to the duration, it includes medium-term trend anomalies and short-term anomalies, and most of them are medium-term trend anomalies. These medium-term trend anomalies are abnormal the annual variation of water level. They also have certain regularity on spatial evolution. The medium-term anomalies are distributed along the fracture zone of the Yangtze River. The results of focal mechanism solution show that the direction of the nodal plane Ⅰ is NE and the nodal plane Ⅱ is NW. The P axis (principal axis) is NE70°, and the dip is 7°. The direction of the main compressive stress obtained by the focal mechanism solution of the Wuwei earthquake is as the same as the distribution of the underground fluid anomalies of the earthquake. It probably indicates that the underground fluid response is closely related to the regional stress loading in the seismogenic process.

Collaboratory for the Study of Earthquake Predictability —Working Philosophy and Achievements of CSEP1.0 ZHANG Sheng-feng, ZHANG Yong-xian EARTHQUAKE    2021, 41 (4): 203-217.   DOI: 10.12196/j.issn.1000-3274.2021.04.016 Abstract （193）      PDF（pc） （5020KB）（138）       Knowledge map    The working routine and research procedure for the earthquake prediction and forecasting began to be discussed after the international debates for the predictability of earthquake started in 1990s. This change gave a new sight for the earthquake researchers for the question that how to conduct an assessment and evaluation for the model performance once a model outputted a forecast result for potential of large earthquakes. To promote the earthquake forecast experiments using likelihood models, the group of Regional Earthquake Likelihood Models (RELM) started by the South California Earthquake Center (SCEC) and it produced hundreds of forecast models in a few years. These models were defined and developed by the seismologists in different research departments. As a following work of the RELM, the Collaboratory for the Study of Earthquake Predictability (CSEP) suggested by SCEC and proposed that different countries and regions should join the test process for different forecast models using rigorous evaluation methods and uniform earthquake data source. In China, the North-South Seismic Belt was suggested as the first testing center (CN-CSEP) in this phase of CSEP work (CSEP1.0). Now the CSEP1.0 has been developed into CSEP2.0 from 2018, and the test region of China has also changed to be the China Seismic Experimental Site (CSES), which has been launched on May 12th, 2018 at the International Conference for the Decades Memory of the Wenchuan Earthquake. In order to make readers understand the working routine and principle for the research related to this international cooperation among different countries and regions, this text gives an outline and a systematically description for the principle and achievements of CSEP1.0 work in recent ten years, as well as the existing problems.

Piezomagnetic Effect Calculation of Earthquakes and Case Analysis SONG Cheng-ke EARTHQUAKE    2022, 42 (3): 52-63.   DOI: 10.12196/j.issn.1000-3274.2022.03.004 Abstract （191）      PDF（pc） （3060KB）（59）       Knowledge map    In this paper, a seismomagnetic phenomenon due to piezomagnetic effect is numerical calculated to help understanding the magnetic anomaly associated with earthquakes. The theory of piezomagnetic effect is introduced and the piezomagnetic field resulting from strike slip fault and dip slip fault are calculated. The pattern of the piezomagnetic field is geometrical symmetry for simple slip model and depends on the strike direction of the fault. The total intensity of the geomagnetic field changes is influenced by the burial depth of slip. According to the piezomagnetic field resulting from two slip models of the 2008 Wenchuan MW7.9 earthquake, larger magnetic field changes occur on slip plane and decays quickly with the distance to epicenter in the bilateral of slip plane. The piezomagnetic field is reduced to about 1 nT or less in area which locates tens kilometres away from epicenter. Based on the observed data of Chengdu geomagnetic observatory before and after the earthquake, a geomagnetic field change of 0.45 nT which is above the background noise level is obtained. The piezomagnetic effect calculated from slip model according to the inversion of geodetic surveying data is consistent with observed data which infers that suitable piezomagnetic model can explain static coseismic geomagnetic changes.

Co-Seismic Fault Slip Distribution of the 2011 Tohoku-Oki MW9.0 Earthquake Retrieved from Co- and Post-seismic Displacements CHEN Wei, LIU Tai, SHE Ya-wen, FU Guang-yu EARTHQUAKE    2021, 41 (4): 121-135.   DOI: 10.12196/j.issn.1000-3274.2021.04.009 Abstract （190）      PDF（pc） （4515KB）（182）       Knowledge map    Based on the viscoelastic sphere dislocation theory, combined with co-seismic data on land and seafloor and 5-10 years post-seismic data from 330 land GPS stations on the main island of Japan, we inverted the fault slip distribution of the 2011 Tohoku-Oki MW9.0 earthquake and improved its rationality in details. Firstly, based on the continuous observation data of 330 land GPS stations on the main island of Japan 2 years before and 10 years after the earthquake, we obtained the annual average displacement of 5~10 years after the 2011 Tohoku-Oki MW9.0 earthquake. The displacement generated during this period can be almost completely regarded as the viscoelastic relaxation of the mantle. Secondly, we used the viscoelastic sphere dislocation theory to simulate the displacements of 5~10 years after the earthquake. Comparing the observed displacement with the simulated ones, we found the optimal viscosity of the mantle is 9.0×1018 Pa·s. Then, we used the viscoelastic Green function and combined co-seismic and post-seismic data to continuously invert the fault slip distribution of the 2011 Tohoku-Oki MW9.0 earthquake. The results showed that the maximum co-seismic dislocation of the 2011 Tohoku-Oki MW9.0 earthquake reached 62.72 meters, and the seismic moment of co-seismic slip was 4.48×1022 Nm, and the corresponding moment magnitude was MW9.03. Since post-seismic displacement caused by the viscoelastic relaxation includes information of the co-seismic slip, the inversion based on the co-seismic and post-seismic data based on the viscoelastic sphere dislocation theory can effectively improve the reliability of the fault slip distribution of the 2011 Tohoku-Oki MW9.0 earthquake. Finally, the inversion method proposed in this paper provides theoretical support for the post-seismic scientific investigation of major earthquakes where the co-seismic data is not enough: the fault slip distribution can be optimized by densifying the observational network and collecting post-seismic data, even if the co-seismic data is not sufficient.

Road Damage Information Extraction from High-Resolution Remote Sensing Images Based on Deeplab V3+ Network Model CHEN Dan-dan, DOU Ai-xia, WANG Xin EARTHQUAKE    2022, 42 (2): 171-189.   DOI: 10.12196/j.issn.1000-3274.2022.02.014 Abstract （189）      PDF（pc） （9607KB）（50）       Knowledge map    After the earthquake, the road is the “lifeline” of earthquake relief. The first time to obtain the road damage information after the earthquake is to minimize the loss of life and property. Aiming at the problems of current seismic damage extraction methods with low accuracy, multiple manual participation and long time consumption, a method for extracting road seismic damage information from single-phase high-resolution remote sensing images based on Deeplab V3+ deep learning network model is proposed. This method fully excavates multi-scale contextual content information, and gradually reconstructs spatial information to better capture road boundaries, thereby improving the accuracy of road earthquake damage information extraction. In this paper, taking the 2013 Lushan M7.0 earthquake in Ya' an of Sichuan Province as an example, by selecting different grades of road high-scoring image samples in mountains, plains, and cities, creating a sample set of model training. In order to further verify the effect of the Deeplab V3+ model, the current more mainstream FCN model is selected for comparison with the Deeplab V3+ model. After multiple training and accuracy analysis, considering the relationship between model accuracy, training quantity and training times. Deeplab V3+ model with 7528 training samples, 100000 training times and 95% total accuracy was selected as the best model. Then, the best Deeplab V3+ model after training is applied to extract post-earthquake road damage information. The results of manual visual interpretation are used as the standard for evaluating the accuracy of model extraction. After comparative analysis, the accuracy of the road information extraction of post-earthquake high-resolution remote sensing images of Deeplab V3+ model can reach 88%. The results show that the method based on Deeplab V3+ model has the highest accuracy and universality, and can be widely used in the rapid extraction of post-earthquake damaged road information.

Study on the Characteristics of the Two-dimensional Tectonic Stress Field in the Focal Area of the Changning MS6.0 Earthquake Sequence on June 17, 2019 TIAN Jian-Hui, LUO Yan EARTHQUAKE    2022, 42 (1): 1-17.   DOI: 10.12196/j.issn.1000-3274.2022.01.001 Abstract （188）      PDF（pc） （8122KB）（72）       Knowledge map    The focal mechanism solution and focal depth of the Changning MS6.0 earthquake sequence in Sichuan on June 17, 2019 were solved using the near-earthquake waveform inversion method, and a total of 30 reliable focal mechanism solutions and focal depths of the earthquakes with M>3.0 were obtained. Combining with the existing focal mechanism solutions in the area, we carry out the inversion of the tectonic stress field in the focal area, and explore the tectonic stress environment in the focal area on a small scale. The inversion results show that the area near the epicenter is dominated by thrust-type stress, and some areas include a small amount of strike-slip components and mixed types. The direction of the maximum principal compressive stress is mainly in the direction of NEE or NE. In the area to the east of Junlian, unlike the thrust type in the north, the stress properties are mainly strike-slip type with a small amount of mixed type, and the maximum principal compressive stress direction is close to the EW direction. There is a certain angle between the direction of the tectonic stress field and the tectonic stress forming the Changning anticline. The 2019 Changning MS6.0 earthquake may be caused by the reverse fault activity at the core of the anticline above the detachment surface of the area caused by the NE or NEE approaching horizontal stress compression.

Study on the Focal Mechanism of the 2020 Qiaojia M5.0 Earthquake and the Stress Field in the Epicentral Area YANG Fan, SHENG Shu-zhong, HU Xiao-hui, CUI hua-wei EARTHQUAKE    2021, 41 (4): 93-105.   DOI: 10.12196/j.issn.1000-3274.2021.04.007 Abstract （185）      PDF（pc） （5955KB）（228）       Knowledge map    Based on the digital waveform from Data Management Centre of National Seismic Network, the focal mechanism solutions of the May 18, 2020 Yunnan Qiaojia M5.0 earthquake and 51 historical earthquakes in the focal area were inverted by using gCAP method, and collect 50 focal mechanism solutions in the study area. Wan’s grid search method is used to invert the tectonic stress field in the seismic source area, and the study area is divided into different divisions for stress field inversion. The results show that: ① the mainshock parameters are as follow, nodal plane I: strike=175°, dip=67°, rake=-19°; nodal plane Ⅱ: strike=273°, dip=73°, rake=156°, the moment magnitude is 4.97, centroid depth is 8.8 km, focal mechanisms represent that the Qiaojia earthquake is a strike-slip event with thrust component. ② The orientation of maximum principal compressive stress axis is NWW in nearly horizontal direction; the orientation of minimum principal compressive stress axis is NNE in nearly horizontal direction; the stress field in source region shows a strike-slip stress regime. ③ The stress field results obtained from the division of different regions are not much different, indicating that the stress field in this region is relatively stable, and is less affected by the type of deep and large faults and focal mechanism solutions.

Evaluation of the ALOS AW3D30 DEM and EIGEN-6C4 Gravity Anomalies in the Northeastern Qinghai—Xizang Plateau ZHANG Guo-qing, LIANG Wei-feng EARTHQUAKE    2023, 43 (1): 93-104.   DOI: 10.12196/j.issn.1000-3274.2023.01.008 Abstract （178）      PDF（pc） （4636KB）（37）       Knowledge map    In this paper, we transferred the normal height of ALOS AW3D30 to GNSS ellipsoidal height based on the EGM96, and analyzed the precision of this digital elevation model in the northeastern Qinghai—Xizang Plateau (QXP) combining with the ground GNSS measurements. We also calculated the gravitational free air anomalies in the northeastern QXP based on the campaign gravity measurements, and evaluated the precision of the EIGEN-6C4 gravitational mode. The results showed that the standard deviation of the difference between ALOS AW3D30 and GNSS results is 3.4 m, which demonstrated that the precision of the ALOS AW3D30 in this region was better than 4 m. The measured gravity anomalies showed generally negative with local positive values, ranging from -177×10-5 to 166×10-5 m·s-2. The modeled gravity free air anomalies of the EIGEN-6C4 changed from -163×10-5 to 142×10-5 m·s-2. The difference between the EIGEN-6C4 gravity anomalies and measured results span from -119×10-5 to 63×10-5 m·s-2, which indicated that the EIGEN-6C4 gravity anomalies were poorly constrained in the northeastern QXP and the measured gravity anomalies should be combined when analyzing gravity anomalies in this region. At last, we fused the EIGEN-6C4 modeled gravity anomalies with the measured ones by the “remove-restore” method, and improved the precision of gravity free air anomalies in the northeastern QXP, especially around the eastern Qilian— Haiyuan Fault and its surrounding areas. The improved regional gravity anomalies can provide a reference for the study of gravity field in the northeastern QXP.

Study on Gravity Potential Energy and Horizontal Deviatoric Stress of the Northeast Qinghai-Tibet Plateau WANG Zhen-yu, FU Guang-yu, LIU Tai, GUO Ling-dong, CHEN Wei, FANG Ting-ting EARTHQUAKE    2022, 42 (2): 1-13.   DOI: 10.12196/j.issn.1000-3274.2022.02.001 Abstract （173）      PDF（pc） （6241KB）（128）       Knowledge map    A quantitative study on the deviatoric stress field of the Northeast Qinghai-Tibet Plateau is of vital importance to reveal the tectonic motion of this region. Based on the in-situ gravity and GPS observations, the current study calculates the gravity potential energy of the study area and evaluates the induced horizontal deviatoric stress, which is then analyzed and compared to the Global Strain Rate Map (GSRM). The results indicate that the gravity potential energy of the study area is featured by a characteristic of high values at the Qinghai-Tibet Plateau and low values at the Ordos Block. The highest value of gravity potential energy locates at the northern Qinghai-Tibet Plateau, with a magnitude of 1.53×1014 N/m, whereas the lowest value of gravity potential energy locates at the southern Qinling Orogen, with a magnitude of 1.45×1014 N/m. The deviatoric stress induced by the difference of gravity potential energy is relatively large at the northern Qinghai-Tibet Plateau, southern Ordos Block, and eastern Qinling Orogen. The largest stress occurs at the conjunction region between the Qinghai-Tibet Plateau and the Alax Block, with a magnitude of about 14 MPa.

The Aftershock Evolution and Earthquake Triggering of the 2022 Menyuan MS6.9 Earthquake YAN Kun, WANG Wei-jun, KOU Hua-dong, YE Zhi-peng EARTHQUAKE    2023, 43 (1): 15-32.   DOI: 10.12196/j.issn.1000-3274.2023.01.002 Abstract （168）      PDF（pc） （11001KB）（56）       Knowledge map    The earthquake sequence’s spatial-temporal evolution can help to reveal the earthquake nucleation process and the interaction between earthquakes. In this paper, we relocated earthquakes in the catalog since 2009 around the 2022 Menyuan MS6.9 focal area with the HypoDD and used them as templates to match-filter re-scan continuous waveforms, building a more complete seismic activity map before and after the mainshock. The results show there was not obvious foreshock pefore the 2022 Menyuan mainshock and it was a typical mainshock-aftershock sequence. Most of aftershocks mainly occurred in a strike-slip fault on the south side of Tuoleshan-north fault, dipping to the south at a high angle. The early aftershocks expanded along strike to the east and west with a logarithm migration relationship between distance and the elapsed time, meeting the rule of the afterslip expansion. The Lenglongling fault oblique intersects with the mainshock’s fault, and its seismicity is different from the aftershocks. The events in the Lenglongling fault occurred before the aftershock expansion front and migrated southeastward along the strike, but soon blocked. The migration continued again only after the MS5.2 earthquake occurred 5 days later, and finally stopped near the end of the 2016 Menyuan aftershock zone. Therefore, the spatial-temporal evolution pattern of the earthquakes indicates the two faults interaction and the seismicity in the Lenglongling fault is probably triggered by the Coulomb stress change from the 2022 Menyuan mainshock.

Preliminary Analysis of Surface Rupture and Seismic Intensity of the 2021 MS5.8 Shuanghu Earthquake in Qinghai-Tibet Plateau ZHANG Jun-long, GONQIU Zhou-ma, CIREN Duo-ji, SUOLANG Nanjie, ZHANG Jian-long, SUN Gou-tao, SIJIN Lou-bu EARTHQUAKE    2023, 43 (1): 65-73.   DOI: 10.12196/j.issn.1000-3274.2023.01.006 Abstract （165）      PDF（pc） （6321KB）（53）       Knowledge map    Field survey showed and steitistics that the macroscopic epicenter of November 30, 2021 MS5.8 Shuanghu earthquake is located near Shenyazadi Village. The maximum intensity of the Shuanghu earthquake could reach Ⅶ degree. Its macroscopic epicenter location, maximum intensity range, major aftershock distribution, etc. are controlled by the fault activity. The surface rupture and seismic mechanism are consistent, which consistently indicates that Wuru cuo fault is the seismic structure.This earthquake produced some clear surface ruptures, which is of great significance for further study of the relationship between magnitude and rupture length.

Joint Application of Shallow Seismic Reflection Exploration and Refraction Tomography in the Haizhou-Hanshan Fault Detection XIA Nuan, WU Zi-quan, FU Jun-dong, ZHANG Jian-min, WANG Dong-lei, PENG Liu-ya EARTHQUAKE    2021, 41 (4): 136-147.   DOI: 10.12196/j.issn.1000-3274.2021.04.010 Abstract （163）      PDF（pc） （7092KB）（38）       Knowledge map    The Haizhou-Hanshan fault is an important fault in the Lianyungang area and belongs to the west boundary fault of the Haisi fault zone. It is buried under the shallow cover and controle the boundary of base rock. The shallow seismic reflection method is the preferred method for fault detection, however, by using this method, the detection of the Haizhou-Hanshan fault can only identify the reflected wave on the top surface of the bedrock, and it is difficult to accurately determine the fault. The refraction tomography method is suitable for areas with large lateral velocity differences, and can obtain the difference information of lithologic velocity between two fault plates, then determine fault locations, which can compensate for the lacks in refleetion method. In this paper, shallow seismic reflection and refraction tomography are jointly applied at the same location of the Haizhou-Hanshan fault, and the drill exploration composite geological section and synthetic seismograms are verified. The research shows that the joint application of the two methods can achieve more accurate fault location than the single method, and more abundant fault information, which provides ideas for fault detection under similar geological conditions.

Ambient Noise Shallow Structure Imaging with Distributed Acoustic Sensing: A Case Study in Fangshan, Beijing KOU Hua-dong, WANG Wei-jun, YAN Kun, YE Zhi-peng, LÜ Heng-ru EARTHQUAKE    2023, 43 (3): 50-65.   DOI: 10.12196/j.issn.1000-3274.2023.03.004 Abstract （158）      PDF（pc） （7771KB）（75）       Knowledge map    Obtaining shallow underground structures in densely populated areas at a low cost and with reliability, is of great importance for both earthquake safety assessments and underground space development. Distributed Acoustic Sensing (DAS) is an emerging observation technology that has developed rapidly in recent years and has different sensing mechanism from traditional seismometers. It can achieve high-density and long-distance vibration measurements using an ordinary communication optical cable and an interrogation unit. We used a 460 m buried optical fiber recorded for 12 hours of background noise in Fangshan, Beijing, to obtain the Rayleigh wave phase velocity dispersion curve and invert the underground shallow S-wave velocity profile. A low-velocity soil layer with a thickness of about 15 m and little undulation, which was similar to the results obtained using the traditional ambient noise H/V spectral ratio method, was observed, however, with more detailed structural information. DAS high-resolution near-surface velocity structure detection is feasible, if existed long-distance buried optical cable resources can be utilized, it will provide a new means for low-cost, high-resolution imaging of the near-surface.

Test Analysis of the Shockproof Reinforcement of Seismometers in Earthquake Observation Station Standardization XIAO Wu-jun, ZHAO Nan, LI Xiao-jun, ZHAO Gang, LIU Quan, QU Li, LUO Jia-ji EARTHQUAKE    2021, 41 (4): 158-167.   DOI: 10.12196/j.issn.1000-3274.2021.04.012 Abstract （157）      PDF（pc） （2588KB）（121）       Knowledge map    In this paper, according to the requirements of earthquake observation stations standardization for the shockproof reinforcement of seismometers and other professional equipment. After the seismic sensors are equipped with shockproof reinforcement devices, the shaking table test and the consistency analysis of the stations observation data are carried out. In the shaking table test, the results show that when the PGA of the seismometer is greater than 103.2 cm·s-2, the seismometer has obvious displacement. So it is recommended to install shockproof reinforcement device where the area with intensity is greater than Ⅶ. In the process of consistency analysis, we use the square coherence method to compare the near earthquake and far earthquake records in the frequency domain and time domain, the results show there is no significant difference in the consistency of seismometer system between the sensor with shockproof reinforcement device and without.

Study on the Regional Assessment Models for the Mortalies Caused by Earthquakes in the Chinese Mainland QI Feng-jiao, LI Wen, SU He-jun, CHEN Wen-kai, WANG Zi-jing, SU Hao-ran EARTHQUAKE    2022, 42 (1): 70-84.   DOI: 10.12196/j.issn.1000-3274.2022.01.005 Abstract （156）      PDF（pc） （3815KB）（110）       Knowledge map    Addressing the large errors in the results of current seismic mortality assessment models in specific regions, the region of Chinese mainland has been zoned as three regions based on seismic hazard characteristics and population distribution, which are northwest region, southwest region as well as eastern region, each region is graded according to population density. The parameters of intensity at the epicenter, seismic area, and seismic fortification intensity were selected, and the multiple non-linear regression method was used to establish a regional model for earthquake mortality assessment. The results show that the models have good validation results in northwest and southwest regions, and could be used for rapid post-earthquake blind assessment. To a certain extent, it can avoid the situation that the evaluation results are the same when calculating earthquakes with different magnitudes, the same epicenter intensity and population density. Although the model needs to be further improved in the eastern part of the country, where there are fewer earthquakes, and in urban direct-downfall earthquakes, it provides ideas for solving the problem of large errors in the assessment of earthquake mortality in specific regions, and can provide data reference for post-earthquake emergency command and rescue.

Earthquake Hazard Analysis of the Bayankala Block and Its Surroundings REN Qing-qing, LU Li-na, QIAN Xiao-shi, ZHAO Yi-bin EARTHQUAKE    2021, 41 (3): 144-156.   DOI: 10.12196/j.issn.1000-3274.2021.03.011 Abstract （156）      PDF（pc） （2842KB）（176）       Knowledge map    Bayankala block and its surroundings have become the important target area because of the frequent earthquake activities. The largest earthquake magnitude is one of the basic parameters in regional seismicity descriptions. It is widely used in seismic risk analysis research. In this paper, we carry out the extreme statistical analysis on Bayankala block and its surroundings using the generalized extreme value distribution. We get the estimation of GEV distribution parameters. Then the recurrence level, the average recurrence period of the earthquakes, the probability of earthquake occurrence and the magnitude of the danger are calculated. We compare the quantile of a level 0.99 for extreme value distribution, the theoretic maximum magnitude from G-R relation and historical maximum magnitude. Finally, the Monte Carlo simulation method is used to verify the stability of the extreme value statistical analysis using the GEV distribution. According to calculation, the average recurrence period of magnitude 6.0 is 1.8 years, and the recurrence period of magnitude 8.0 is only 76.8 years. The 100-year reproduction level is as high as 8.08. In addition, the probability of occurrence of an earthquake of magnitude 5.0 to 7.0 in this block is relatively high, which indicate that the block will still active in the future. Monte Carlo simulation results show that the use of GEV distribution to explore the seismic hazard of this block is stable to a certain extent.

Double-difference Seismic Tomography of the 3D P-wave Velocity Structure of Major Fault Zones and Adjacent Areas in Northwest Yunnan YANG Feng EARTHQUAKE    2021, 41 (3): 42-58.   DOI: 10.12196/j.issn.1000-3274.2021.03.004 Abstract （155）      PDF（pc） （11082KB）（148）       Knowledge map    We determined a 3D P-wave velocity model of the middle and upper crust under the northwest Yunnan (25°~28.2°N, 99.5°~101.5°E) by using double-difference seismic tomography and jointly inverting 60471 absolute arrival times and 196465 differential arrival times from 7349 local events recorded by permanent seismic network and ChinArray. Our results show that a low P wave velocity zone is existed above 15 km in the northern section of the Jinshajiang-Red River fault zone, and majority of hypocenters are located in low velocity anomalies and focal depths are similar on both sides of the fault zone. We speculate that the role of the Jinshajiang-Red River fault zone as the southwest boundary of the Sichuan-Yunnan diamond block is weakening, and low velocity anomalies below the fault zone may helpful to dynamic transmission across the fault zone. There are large range of low velocity anomalies on both sides of the southwest section of the Lijiang-Xiaojinhe fault zone, and we deem that these low velocity anomalies may be the Tibetan plateau material which have been extruded. On the east of Chenghai fault zone, there are obviously P wave high velocity anomalies from near surface to 25 km depth, and these high velocity anomalies may block the southeastern escape of the plateau material.

The 7th General Election and Academic Seminar of Seism-Electromagnetics Committee, Seismological Society of China were Successfully Held ZHANG Yu EARTHQUAKE    2022, 42 (2): 190-191.   DOI: 10.12196/j.issn.1000-3274.2022.02.015 Abstract （154）      PDF（pc） （225KB）（106）       Knowledge map

Q-value Characteristics of Seismic Coda about the Earthquake Swarm Occurred in Junction Area between Lingyun County and Fengshan County of Guangxi Zhuang Autonomous Region in 2010 SHI Shui-ping, ZHOU Bin, LI Xi-guang, WEN Xiang, HUANG Hui-ning, MAO Shi-rong EARTHQUAKE    2021, 41 (4): 106-120.   DOI: 10.12196/j.issn.1000-3274.2021.04.008 Abstract （152）      PDF（pc） （4867KB）（179）       Knowledge map    During June 28 to early August in 2010, a small earthquake swarm occurred in the junction area between Lingyun County and Fengshan County, Guangxi Zhuang autonomous region. Based on the digital seismic waveforms recorded at 8 near-field seismic stations, 179 three-component records in 74 ML>1.5 earthquakes selected according to the high signal-to-noise ratio and calculation requirements, after filtering the seismic waveform record to eliminate background noise by using the Sato single scattering model, we calculated the coda Q(f) and obtained the relationship between coda Q(f) and frequency (f) to be Q(f)=(44.32±23.56)f0.88±0.17 in the studied area. Then, the spatiotemporal characteristics of seismic wave attenuation in source region and its adjacent regions are discussed. Analysis on the relationship between attenuation parameters and sampling depth of the seismic region and its adjacent areas suggests that there may exist shallow high attenuation layers beneath the study region. The earthquake swarm occurred at low stress levels, with higher Q0 value and slower seismic wave attenuation in the source area than that of other stations, which suggests that the level of non-uniformity properties of the crustal medium is low in the source area with stable medium and slow attenation.

Characteristics and Mechanism of Borehole Strainmeter in Response to a Squall Line in East China YANG Xiao-lin, YANG Jin-ling EARTHQUAKE    2021, 41 (4): 180-191.   DOI: 10.12196/j.issn.1000-3274.2021.04.014 Abstract （150）      PDF（pc） （3791KB）（173）       Knowledge map    On 4 March 2018, a southwest-northeast-oriented squall line was observed propagating across East China, which caused disaster during its evolution. The main object of this work is to systematically reveal the characteristics of the squall line in strainmeter measurements, and to improve our understanding of atmospheric loading signals in strainmeter records during the passage of the mesoscale convective system. Combined with the doppler radar, atmospheric pressure and outdoor temperature observations, we analyze the responses of volumetric strain with 1-minute resolution to the strong squall line recorded at Nanchang, Huangshan, Huzhou, and Daishan stations. The results show that: ① The short-period jump in the atmospheric pressure caused by the squall line is the main dominating driving force for the pressure-induced volumetric strain, the maximum magnitude is about 16.2×10-9 on strain records. ② It is also observed the relationship between the fluctuations of atmospheric pressure and the compressive strains as for the magnitudes for the above-mentioned stations show a good linear variations. And the observed fluctuations with a periodicities ranging from 26 to 74 minutes are almost consistent between the atmospheric pressure and volumetric strain. Moreover, the atmospheric pressure coefficient of volumetric strain can reach up to 5.0×10-9/hPa. ③ All the stations can respond well to the squall line. Furthermore, the evolution process and propagating pattern of the spatiotemporal and intensity variations for the squall line can be revealed clearly by multi-station records. The results could lead to reasonably uncover the physical origin of anomalous volumetric strain changes recorded at single-and/or multi-station. Meanwhile, the results can also contribute to providing the crucial observational evidences for atmospheric loading model in short period aiming to correct barometric effect precisely.

Inversion of the Rupture Process of the 2022 Luding MS6.8 Earthquake by Regional Seismic Data WANG An-jian, LI Guo-hui, GAO Yuan EARTHQUAKE    2023, 43 (1): 33-41.   DOI: 10.12196/j.issn.1000-3274.2023.01.003 Abstract （149）      PDF（pc） （6162KB）（66）       Knowledge map    On September 5, 2022, an MS6.8 earthquake occurred in Luding County, Ganzi Tibetan Autonomous Prefecture, Sichuan Province. In this study, we analyzed regional seismic data and inverted the focal rupture process of the main shock. The results show that the seismic fault of this earthquake is the Xianshuihe fault of generally left-lateral strike-slip. The rupture propagated primarily in the SSE direction along the fault strike, expanding from the initial rupture point to the shallow part. The duration of the entire process was approximately 13 s, releasing a scalar seismic moment of 1.2×1019 N·m, equivalent to MW6.6. The rupture had a length of about 18 km and a width of 14 km, with a maximum coseismic slip of 2.7 m and an estimated centroid depth of 6.2 km. Comparing our inversion results with those obtained from teleseismic waveform data, we conclude that the main rupture area of this earthquake is located on the SSE side of the epicenter, while no obvious rupture area is observed on the NNW side of the epicenter.

The Abnormal Characteristics and Mechanism of Cross-fault Deformation in the Seismogenic Zone before the 2022 Menyuan M6.9 Earthquake LI Yuan, CHEN Chang-yun, LI La-yue, ZHOU Wei EARTHQUAKE    2023, 43 (1): 1-14.   DOI: 10.12196/j.issn.1000-3274.2023.01.001 Abstract （149）      PDF（pc） （4410KB）（77）       Knowledge map    Cross-fault deformation measurements have made an important contribution to the search for earthquake precursor information and strong earthquake prediction and forecasting efforts. Before the 2022 Qinghai Menyuan M6.9 earthquake, the cross-fault data in the Qilianshan-Haiyuan fault zone occured significant precursory anomalies. Based on the cross-fault data before earthquake, this paper uses time-series analysis, deformation anomaly intensity analysis, vertical deformation accumulation rate analysis and other methods to extract the temporal and spatial evolution characteristics of pre-earthquake anomalies, and analyse the short-term and medium-term fault activity and deformation mechanism before the earthquake. The results show that under the dynamic background of the combined action of NE-trending extrusion and NW-trending horizontal shear, the accumulation of deformation trend in the near-seismic region and its vicinity is at a high value, with a certain degree of strain accumulation background. Five years before the earthquake, the movement of the faults in the near-seismic area deviates from linearity and slows down. During the two years before the earthquake, the abnormal spatial distribution has the characteristics of migration and concentration to the epicentral area, which indicates that the crustal stress is accumuleting rapidly and locally enhanced in the near-epicentre area. Within half a year before the earthquake, multiple sites in the region of 60~120 km from the epicenter exhibited consistent tensional anomalies that were opposite to the compressional background, implying that micro-dynamic adjustment occurred after the stress in the near-seismic area accumulated to a certain extent, and pre-slip behaviors occurred.

Research on Prediction Index System of Seismo-magnetic Vertical Intensity Polarization and Its Application GUAN Yi-liang, HE Chang, FAN Wen-jie, HE Man-qiu, LIAO Xiao-feng, LI Xia, LIU Su-zhen, YUAN Wen-xiu, AISA Yisimayili, FENG Li-li EARTHQUAKE    2022, 42 (4): 159-174.   DOI: 10.12196/j.issn.1000-3274.2022.04.013 Abstract （147）      PDF（pc） （5924KB）（38）       Knowledge map    This paper calculates the vertical intensity polarization by using the second data at 88 geomagnetic stations during 2015 to 2021, and systematically summarizes the calculation method of polarization value and the criterion of polarization anomaly discrimination by combing time-space relationship between high-value anomalies and earthquakes. And on this basis, we extract the quantifiable prediction index, which is defined as: ① more than 20% of stations have polarization values higher than two times of the mean square error and continue three days. ② The anomaly area is a space with normalized zero polarization value greater than 0.2. ③ The dominant time of earthquake occurrence is within six months. ④ The earthquake magnitude is positively related to the size of the anomaly area. According to the above criteria, 16 groups of anomalies (32 abnormal areas) are extracted. The prediction efficiency evaluation results show that R-value (R=0.53) is higher than R0-value (R0=0.234) with 97.5% confidence level, based on the analysis of seismic examples of accurate report, false report and missing report. Here, we analyze the magnetic disturbance characteristics before the 2021 Maduo, Qinghai M7.4 earthquake using polarization method. The result shows that the synchronous high-value anomaly occurred 16 days before the earthquake, more than 20% of stations has polarization anomalies that last three days and the anomaly area is 14.1×104 km2. This anomaly which is up to the standard of index system can be determined as a pre-earthquake polarization anomaly. The study suggests that the above prediction index system has obvious earthquake prediction significance, can be used to extract the polarization anomaly before strong earthquake, and can provide reference for earthquake situation determination.

Effect of Sensor Placement Depth on Dynamic Characteristics of Water Temperature and Its Mechanism Analysis CHEN Qi-feng, CHE Yong-tai, LIU Yun, FENG En-guo, WEN Li-yuan EARTHQUAKE    2022, 42 (1): 169-180.   DOI: 10.12196/j.issn.1000-3274.2022.01.013 Abstract （146）      PDF（pc） （3818KB）（157）       Knowledge map    According to observation specifications of geothermal wells, the water temperature sensors should be placed as deep as possible. Generally, the depth is more than 100 m and less than 200 m. However, it is observed that the placement depth of water temperature sensors has a significant effect on the dynamic characteristics of water temperature observation. In most observation wells, the dynamic characteristics between water temperature and water level in the same well, such as time dynamics, tidal effects, co-seismic responses and post-earthquake step-changes, show high correlations or consistencies, which is usually relevant to the placement depth of water temperature sensors. In this paper, the dynamic characteristics of water temperature affected by sensor placement depth is discussed, when the water temperature sensor is placed in the observation aquifer, it is affected by the flow movement between the well and the aquifer, which will cause the water temperature changes with the change of the well water level; when placed under the observation aquifer, the water temperature is not affected by the change of well water level, and most of the dynamic is relatively stable. This is mainly because the formation of water temperature dynamics is controlled by two different mechanisms, hydrothermal dynamics and geothermal dynamics, and the conditions of the well-aquifer system also play a role.

Measurement of the Data Transfer Function of the Force Balance Feedback Quartz Horizontal-pendulum Tiltmeter JIANG Feng, GAO Shang-hua, XUE Bing, LI Ji-hong EARTHQUAKE    2022, 42 (2): 52-62.   DOI: 10.12196/j.issn.1000-3274.2022.02.004 Abstract （145）      PDF（pc） （1860KB）（94）       Knowledge map    This paper presents a method to dynamically test the data transfer function of the quartz horizontal-pendulum tiltmeter by using step voltage signal and sine wave voltage signal as calibration signals. We firstly introduced the addition way of the calibration signals to the tiltmeter and derived the expressions of the transfer function and the outputs of force balance feedback quartz horizontal-pendulum tiltmeter when calibration signals were input. Afterward, we performed test experiments and got the tiltmeter' s output responses of the sinusoidal calibration and the step calibration. Based on the above-mentioned test results and using the derived theoretical formula, we carried out nonlinear fitting of sinusoidal calibration output response and step calibration output response respectively, and obtained the period and damping of the force balance feedback quartz horizontal-pendulum tiltmeter according to the fitting results. The laboratory test results show that the period and damping obtained by sine wave calibration test are in good consistent with those obtained by step calibration test, which verifies the effectiveness and consistency of the test method presented in this paper.

Relocation of Seismic Activity in Gaizhou Area Based on TomoDd Method QIAN Rui, WANG Liang, ZHANG Bo, YANG Shi-chao, SHAO Yuan-yuan EARTHQUAKE    2022, 42 (2): 149-160.   DOI: 10.12196/j.issn.1000-3274.2022.02.012 Abstract （144）      PDF（pc） （5834KB）（135）       Knowledge map    The activity of the Gaizhou earthquake swarm since 2012 is one of the most significant seismicity events in Liaoning in recent years. According to the previous research results, the Gaizhou earthquake swarm is periodically active in time, and the space is divided into two areas: Qingshiling and Xihaiyu, all of which are distributed in the northwest to near east-west direction,but most of the research results only discuss and analyze the earthquake swarm since 2012.In this paper, the tomoDd method is used to relocate the activity of small earthquakes in Gaizhou area since 1980. Through comparative analysis of the spatial location relationship between these swarm activities since 2012 and the previous swarm activities, it is found that there have been similar scale earthquake activities in Gaizhou area from 1982 to 1989, and the spatial concentration of earthquakes is high, which proves that there is a tectonic background for cluster earthquakes in Gaizhou and nearby areas.The earthquake swarm activity since 2012 may belong to another earthquake swarm activity in this area, and its precursory indication significance is limited.

Analysis of Seismic Thermal Anomaly in Yutian Area of Xinjiang, China Based on Multi-Source Remote Sensing Data of Different Spatial and Temporal Scales DU Chen, SUN Ke EARTHQUAKE    2022, 42 (3): 37-51.   DOI: 10.12196/j.issn.1000-3274.2022.03.003 Abstract （142）      PDF（pc） （6813KB）（66）       Knowledge map    Based on the MODIS land surface temperature data and NOAA outgoing longwave radiation data of 5 earthquakes with MS5.0 or above in Yutian area since 2000, the characteristics of thermal infrared anomalies before earthquakes are extracted and analyzed from different time and space scales. The results show that obvious thermal anomalies are extracted from the two kinds of data of the five earthquakes, and the extraction results of the two data anomalies have a certain temporal and spatial correlation. Based on the above analysis results of thermal infrared characteristics of different spatial and temporal scales, an multi spatial and temporal scale anomaly discrimination method is summarized and put forward. Based on this method, the thermal infrared data of the field and its surrounding areas from 2018 to 2020 are scanned, and the retrospective test application of thermal infrared anomalies of earthquakes above MS5.0 is carried out. A total of 19 anomalies are detected, including 12 corresponding earthquakes, 7 false reports. In addition, there are 7 missed reports. The comprehensive extraction of thermal infrared anomaly features from multi-source remote sensing data of different spatial and temporal scales can reduce the interference of environmental factors and extract effective thermal anomaly features. The above research results provide support for the identification of seismic thermal infrared anomalies in multi temporal and spatial scales.

Analysis of the Change of Gravity Field before and after the 2022 Qingzhou ML4.1 Earthquake ZHENG Jia-jun, LI Bo, ZHU Cheng-lin, HUANG Jin-shui, YANG Li-tao, DONG Min, XIONG Wei, HAN Bo, LIU Hai-lin, CHI Guo-min, WU Jing EARTHQUAKE    2023, 43 (3): 102-119.   DOI: 10.12196/j.issn.1000-3274.2023.03.008 Abstract （142）      PDF（pc） （8351KB）（74）       Knowledge map    In this paper, the 2022 Qingzhou ML4.1 earthquake was taken as the research target. According to the abnormal characteristics of regional gravity field changes in the preparation and occurrence of large earthquakes summarized by previous scholars, the spatial scale and order of magnitude of changes near the epicenter were analyzed by means of calcalating gravity changes in two adjacent periods and cumulative gravity changes. The variation of the single point of the measuring points in the area with significant variation of regional gravity field, including Gaobingxi, Jinan Station, Wangfen and Miaozi, as well as the variation of gravity difference between the north and south of the Gaobingxi site, was also analyzed. According to the surrounding disturbance of the two measuring points in the Gaobingxi site, including the precipitation, land subsidence and terrain correction, the reasons for the change of gravity difference between the two measuring points were analyzed. It is suggested that the gravity field changes before and after the Qingzhou ML4.1 earthquake, and the change is related to the underground material migration caused by the earthquake preparation and occurrence.

Spatio-Temporal Evolution of Electric Field Pre-and Post-Earthquakes with Magnitude MS≥5.0 in Northeast Asia YANG Mu-ping, ZHANG Xue-min, ZEREN Zhi-ma, SHEN Xu-hui, HUANG Jian-ping, QIAN Geng, JIN Yan-ming, HUANG Ming-wei EARTHQUAKE    2021, 41 (4): 78-92.   DOI: 10.12196/j.issn.1000-3274.2021.04.006 Abstract （140）      PDF（pc） （5865KB）（184）       Knowledge map    Five frequency bands of the power spectrum density data of the electric field in the ELF/VLF frequency band (39~6000 Hz) recorded by the microsatellite DEMETER from January 2005 to February 2009 is utilized to carry out statistical analysis about the spatio-temporal evolutions of electric field during the 8 strong earthquakes with magnitude MS≥5.0 in Northeast Asia (38°N~58°N; 105°E~145°E). The analysis shows the perturbations in different frequency bands of the same earthquake are not all in the same regions. And the perturbation patterns in different frequency bands of the same earthquake are not consistent during the same earthquakes. Statistical analysis of perturbation amplitude during the 8 earthquakes shows that for the 25% of these statistics shows no obvious spatial and temporal patterns, although the perturbation amplitude reached basically more than 2 times the standard deviation during the earthquakes. The remaining 75% of the statistics can be classified into three types: the perturbation amplitude of the 52% of the statistics began to increase before the earthquake, and the earthquake occurred at the high perturbation stage. For the 7.5% of the statistics, the perturbation amplitude increased to the high perturbation stage before the earthquake, and the earthquake occurred during the descent stage of the perturbation amplitude. For the 15% of the statistics, the perturbation amplitude increased and reached basically less than 2 times the standard deviation before the earthquake, and the perturbation amplitude of the fifth frequency band in these earthquakes are all in this type. The perturbations mainly appear in the places outside ±4° in latitude and in longitude from theepicenter.