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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。

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.

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.

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.

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.

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.

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.

Review on the Research of Asperity Identification and Cascading Rupture in Forecasting of Earthquake Magnitude WEI Bin, LIU Qi, WANG Zhen-yu, XU Yue-yi, SHAO Zhi-gang EARTHQUAKE    2023, 43 (3): 1-17.   DOI: 10.12196/j.issn.1000-3274.2023.03.001 Abstract （139）      PDF（pc） （7964KB）（116）       Knowledge map    The magnitude forecasting of strong earthquakes is of great scientific significance, and also plays an important role in the actual work of earthquake prevention and disaster reduction. Based on relevant research progress at home and abroad, this paper focuses on the identification of asperities and cascading ruptures in magnitude forecasting of strong earthquakes. The occurrence of earthquakes usually relates to the destruction of asperities. For the identification of asperities, comprehensive analysis can be carried out mainly from the aspects of the media nature in the seismogenic zone, small-medium seismicity, fault motion state, stress state, friction attribute, etc. The occurrence of cascading ruptures will increase the magnitude of earthquakes and the risk of earthquake disasters. The factors controlling its probability mainly include the geometric properties of faults, such as fault surface curvature, geometry change, step distance, as well as, the physical properties of fault and surrounding media, such as the friction properties of fault surfaces, changes in the width of seismogenic layer in adjacent fault segments, stress distribution of fault surfaces and shallow low-velocity fault zones. The research of relevant models and parameters depends on the development of intensive observation, fault exploration and other basic work, the application of numerical simulation, inversion and other technologies, and the integration of multiple disciplines. It is hoped that this paper can provide a reference for the forecasting of strong earthquake magnitude in key fault sections of the Chinese Mainland.

The Variation Characteristics of Gravity Field Before Lusan MS6.1 Earthquake and Maerkang MS6.0 Earthquake in 2022 ZHENG Bing, MA Ling-li, WANG Wei-li, YI Tian-yang, WEN Jun-jun, LIU Hong-wei, CUI Jing-feng, ZHU Ren-guo, BAI Yun-bo EARTHQUAKE    2023, 43 (1): 42-53.   DOI: 10.12196/j.issn.1000-3274.2023.01.004 Abstract （133）      PDF（pc） （6158KB）（54）       Knowledge map    The gravity value of the Earth's surface will change accordingly in the process of earthquake preparation. We draw the contour maps of gravity field by using the mobile gravity observation data in Sichuan area from March 2018 to April 2022 and we study the variation characteristics of the gravity field before Lusan MS6.1 earthquake and Maerkang MS6.0 earthquake in 2022 by the contour maps. The results show: ① It was a period of intensive changes in gravity that about one and a half years before the Lusan MS6.1 earthquake and Maerkang MS6.0 earthquake. ② The Lusan MS6.1 earthquake advanceed the occurrence of the Maerkang MS6.0 earthquake; ③ The four quadrant area of the gravity variation contour before Lusan MS6.1 earthquake and Maerkang MS6.0 earthquake indicate a high concentration of stress in the area; ④ The epicenters of the Lusan MS6.1 earthquake and Maerkang MS6.0 earthquake were near the zero value line and has a large turning arc and are possible or high risk area for a large earthquake in the tectonic belt.

Characteristics of Deep and Shallow Tectonics Deformation in Southwest Yunnan YANG Ye-xin, MENG Guo-jie, WU Wei-wei, LUO Yan, Thant Myo EARTHQUAKE    2023, 43 (1): 74-92.   DOI: 10.12196/j.issn.1000-3274.2023.01.007 Abstract （125）      PDF（pc） （8445KB）（62）       Knowledge map    Southwest Yunnan is an earthquake active area. The deep and shallow deformation characteristics of the lithosphere in this area is of great significance to understand its seismogenic environment and mechanism. This study is based on independent observation and collected regional GNSS data, the GNSS velocity field in Southwest Yunnan is studied. Then the multi-scale spherical wavelet method is used to calculate the strain rate tensor, and the spatial distribution characteristics of principal strain rate, surface strain rate and maximum shear strain rate are analyzed. The results show that the southwest of Yunnan is compressed by nearly NNE—SSW, and the surface compressibility is ~10 nstrain/a. The near east-west fault is characterized by left-hand strike slip, and the near north-south fault is characterized by right-hand strike slip. There is an obvious transformation between surface compression and surface expansion in the area between Heihe fault and Wuliangshan fault. Wanding fault, east of Longling-Ruili fault, east of Nantinghefault, Heihe fault, Lancang fault and Xiaojiang fault extend across Honghe fault to Menglian-Mengxing fault area has high shear strain rate, up to 50 nstrain/a. The focal mechanism solutions of the study area from 1976 to 2020 are collected, the regional damping stress inversion method is used to invert the stress tensor, and the R-value distribution reflecting the relative size of the principal stress is attained. The inversion results show that the southwest of Yunnan is affected by the principal compressive stress in the NNE—SSW direction, and the area is in the state of strike slip stress as a whole, The North-south fault near Tengchong volcano in the east of Dayingjiang fault has the characteristics of normal fault and oblique slip. The magnitude of principal stress in Southwest Yunnan is obviously different in space. The south of Nantinghe fault is the area with the largest principal stress, and its strike slip characteristics are more obvious. In addition, this study also collects seismic wave anisotropy data in the study area, compares the angle between the direction of the principal stress axis and the principal strain rate axis, the angle between the direction of the principal stress axis and the polarization direction of Pms fast wave, the angle between the direction of the principal stress axis and the polarization direction of XKS fast wave, the angle between Pms fast wave direction and XKS fast wave polarization direction, we obtains the structural deformation differences between the surface and middle upper crust, middle upper crust and lower crust, lower crust and upper mantle respectively, It is found that the lower crust and upper mantle are decoupled in Southwest Yunnan. At the same time, it is found that the difference in deformation between the lower crust and the middle upper crust near Longling-Ruili fault, Nantinghe fault and Menglian fault, indicating that the lower crust and the middle upper crust are decoupled in this area, and there may be a hot material flow channel in the lower crust, with localized lower crustal flow in partial zones of southwestern Yunnan.

Geochemical Characteristics of Soil Hydrogen Gas of the Main Seismogenic Structures of Songliao Basin LI Ji-ye, HU Lan-bin, KANG Jian, LI Ying, WANG Qiang, SUN Qiang, ZHANG Yan-xiang EARTHQUAKE    2023, 43 (1): 152-170.   DOI: 10.12196/j.issn.1000-3274.2023.01.012 Abstract （122）      PDF（pc） （5918KB）（52）       Knowledge map    The geological structure in the central part of the Songliao Basin is well-developed, with a complex system of intersecting faults. In the past, the area has experienced several strong earthquakes, with the main seismogenic structures being the Fuyu-Zhaodong Fault and the Hulanhe Fault within the Songliao Basin. Soil hydrogen gas measurements were conducted on the Fuyu-Zhaodong Fault and the secondary faults of Hulanhe Fault, namely the Suihua-Menggushan Fault, revealing significant changes in soil hydrogen gas levels near the active fault zones. The results show that ① the hydrogen gas anomaly threshold concentration ratio for each measuring line in the Fuyu-Zhaodong Fault was 1.8~2.3, with an anomaly peak concentration ratio of 3.0~6.4; ② the hydrogen gas anomaly threshold concentration ratio for each measuring line in the Suihua-Menggushan Fault was 1.8~2.5, with an anomaly peak concentration ratio of 3.5~5.7; ③ comparison of the abnormal background, threshold, and peak concentrations between the two faults indicated that the values for the Fuyu-Zhaodong Fault were significantly higher than those for the Suihua-Menggushan Fault. This may be related to the recent significant seismic activity of the Fuyu-Zhaodong Fault, possibly containing information about the enhancement of pre-earthquake tectonic activity. ④ Significant changes in soil hydrogen gas were observed near active fault zones, which may be related to the nature of the two faults, geological structure units, local stress environments, and the strength of fault activity.

Application of CEEMDAN in GNSS Time Series Analysis LIU Xi-kang, DING Zhi-feng, LI Yuan, LI Jin-wu EARTHQUAKE    2022, 42 (3): 99-110.   DOI: 10.12196/j.issn.1000-3274.2022.03.007 Abstract （116）      PDF（pc） （5096KB）（64）       Knowledge map    The validity and reliability of the Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) method in the data analysis and processing are verified by processing the simulated signals. Using this method to decompose the N, E and U direction time series of 10 GNSS (Global Navigation Satellite System) continuous stations, it is found that not only annual and semi-annual period signals exist, but also shorter or longer period signals exist in some stations, and the vertical periodicity is more obvious than the horizontal direction, and the corresponding amplitudes are larger. The average WRMS (Weighted Root Mean Square error) of the time series in the N, E, and U directions was reduced by 19.8%, 19.0%, and 29.9%, respectively, compared to the original N, E, and U directions after the periodic term correction, indicating the effectiveness of the method for periodic term correction.

Rayleigh Wave Phase Velocity and Azimuthal Anisotropy across Haiyuan Fault Zone and Its Adjacent Area Derived from Ambient Noise Tomography CHE Zi-qiang, WU Zhong-liang, GAO Yuan EARTHQUAKE    2023, 43 (1): 105-123.   DOI: 10.12196/j.issn.1000-3274.2023.01.009 Abstract （113）      PDF（pc） （10587KB）（35）       Knowledge map    Haiyuan fault zone is a large NWW-trending boundary fault zone located on the northeastern margin of the Qinghai-Tibet Plateau. In order to study the crustal velocity structure and deformation characteristics of this region, the Cross-Haiyuan Fault Zone temporary Seismic Array set up by the Institute of Earthquake Forecasting, China Earthquake Administration (SACHY-Array) and vertical continuous waveform data of a total of 61 stations (including 40 temporary stations and 21 permanent stations) of permanent seismic stations in the study area were used. Based on the background noise cross-correlation method, the surface wave phase velocity dispersion curve were extracted, and the Rayleigh wave phase velocity and azimuth anisotropy images with a period range of 5~30 s and a resolution of 1°×1° were obtained by inversion. The results show that, within a short period of 5~10 s, the eastern Hexi Corridor transition zone, the northwestern Ordos Block, and the southern Yinchuan graben all present low-velocity anomalies, while the eastern Qilian orogenic fold belt presents relatively high-velocity; the southwest side of the Haiyuan fault zone presents fast waves the polarization directions are NWW and NW. The polarization direction of fast waves in the western margin of Ordos Block and its adjacent areas is mainly near NS, and the anisotropy direction is basically consistent with the regional fault strike. In the period of 15~30 s, the low-velocity anomalies in the east of the Hexi Corridor transition zone and the southern part of the Yinchuan Graben gradually weakened, and the range continued to decrease. Around the 15 s period, the low-velocity bodies in the east of the Hexi Corridor transition zone were staggered under the Yantongshan fault zone. There are high-speed anomalies in the center of the Longzhong Basin and the southwestern margin of Ordos; the direction of azimuthal anisotropy is basically consistent with the short period, but the anisotropy intensity is weak. The authors believe the Haiyuan fault zone is a transition zone between high and low velocities. The Hexi Corridor transition zone on the north side of the fault zone exhibits low velocity anomalies, while the Qilian fold orogenic belt on the south side exhibits high velocity anomalies, indicating that the Haiyuan fault zone and its adjacent areas have complex crustal structures and may have local crustal deformation and destruction; the azimuthal anisotropy of the crust is an important constraint index of crustal deformation, indicating that the anisotropy of the Haiyuan fault zone and its adjacent areas may be mainly caused by the shear deformation of the crust in the northeastern margin of the Qinghai-Tibet Plateau, the north-east pushing of the Qinghai-Tibet Plateau is the main source of dynamic in this area.

Carding Seismic Belts and Summarizing Prediction Indexes in Ningxia LUO Heng-zhi, LUO Guo-fu, MA He-qing, XU Ying-cai, LI Wen-jun EARTHQUAKE    2023, 43 (3): 178-189.   DOI: 10.12196/j.issn.1000-3274.2023.03.013 Abstract （113）      PDF（pc） （3906KB）（164）       Knowledge map    By retrospectively collating seismic belt anomalies in Ningxia since 1970, we analyzed the temporal and spatial characteristics of seismic belt anomalies, as well as, the anomaly threshold of internal and external seismic frequency ratio, obtained the parametric fitting equations of major earthquake and seismic belt, summarized and the prediction indexes of seismic belt in Ningxia, which provides some support and basis for the short-term earthquake tracking, discussion and evaluation technical schemes in Ningxia. The results showed that ① There were 12 significant seismic belts with ML≥2.5 in Ningxia and its adjacent areas since 1970, among which, 8 earthquakes with M≥5 occurred at the end of the strip within one year after the end of the belts, and the dominant seismic reflection period was half a year, which could pass the R-value scoring test of prediction efficiency, and had certain medium-term prediction significance. ② There was a good linear positive correlation between the onset time, magnitude of the main earthquake, and the length, duration, total energy of the belt. The reference mean value could be given by the regression equation. The end of the belt was a favorable place for the occurrence of moderate strong earthquakes in the future. ③ In Ningxia, the average frequency ratio of the inner and outer belt was generally low. During the formation of the seismic reflection belts, there was a significant high value more than 0.75 but less than 2 times the mean square error, and the abnormal high value of the falsely reported belts was not significant.

Phase Picking and Earthquake Location based on Deep Learning in the Baihetan Reservior Area ZHANG Yu-cheng, HUA Wei EARTHQUAKE    2023, 43 (1): 137-151.   DOI: 10.12196/j.issn.1000-3274.2023.01.011 Abstract （112）      PDF（pc） （9755KB）（32）       Knowledge map    In recent years, deep learning technology has become increasingly prevalent in seismic phase picking and earthquake location research. This paper employs the EQTransformer, a deep neural network, to pick P and S arrivals from continuous data recorded by 34 digital seismic stations in the Baihetan reservoir area from 2016 to 2018. Phase association and preliminary localization by REAL, followed by optimization of earthquake location using VELEST and hypoDD. The research reveals that seismic phase picking based on deep learning is significantly more efficient than traditional manual methods in the Baihetan Reservoir area. The accuracy of the EQTransformer-picked P and S first-arrivals is comparable to that of manually picked phases, with average time differences of 0.03 s and 0.07 s, conforming to a normal distribution. The number of events after preliminary location by REAL (13815) is nearly twice of the routine catalog (7862), and we ulfimately obtain high-precision locations of 7108 earthquakes by the hypoDD. The estimated magnitude is on average 0.27 lower than that in the routine catalog, and the magnitude difference is primavily within 0.7. The minimum magnitude of completeness is changed from ML1.4 in the routine catalog to ML0.6+0.27, effectively filling the magnitude gap of the routine catalog and enriching the data on moderate and small earthquakes in the Baihetan reservoir area.

Rayleigh Wave Phase Velocity Maps of Southwest Yunnan Based on Ambient Noise Tomography ZHANG Yi, GUO Zhen, ZHU Pei-yu, ZHU Jia-miao, DAI Le-xiang EARTHQUAKE    2023, 43 (1): 124-136.   DOI: 10.12196/j.issn.1000-3274.2023.01.010 Abstract （111）      PDF（pc） （13055KB）（32）       Knowledge map    In this paper, the phase velocity distribution images of Southwest Yunnan (21.0°N~29.5°N, 97.0°E~103.5°E) are obtained with continuous seismic records at 190 mobile stations in the first periods of ChinArray (2011-01—2014-06) and 35 broadband permanent stations of Yunnan regional network. The ChinArray was setup in the southeast of the Qinghai-Xizang Plateau. Inversion results reveal significant lateral heterogeneity in the velocity structure of the crust and upper mantle in the study area. Short period images (6~12 s) indicate a strong correlation between upper crust velocity and surface geological structures. The low velocity anomaly in Tengchong volcanic area and its southern side is related to the magmatic sac or partial melt in the upper crust, and the shape is different in depth. A high-velocity anomaly is observed between Chenghai fault and Puduhe fault, consistent with the body wave travel time inversion results. The inversion indicates a large high-velocity anomaly in Panxi area, potentially related to basalt uplift in this area. Phase velocity images with periods of 14~25 s reveal low-velocity anomalies in the Sichuan-Yunnan rhombic block and Tengchong volcanic area, suggesting the presence of lower crustal flow. Comparing 14~40 s images, due to variations in crustal thickness, the high-velocity anomaly gradually increases in the southern region. Furthermore, the low-velocity anomaly in the Tengchong volcanic area extends from the surface to the upper mantle, but it does not appear to be continuous with the low velocity anomaly in the Sichuan-Yunnan rhombic block. This low velocity anomaly may be a channel of mantle heat flow. The intersection of the Tengchong fault and Longling fault appears to be the boundary between high and low-velocity anomalies. Two M≥7 earthquakes in 1976 may occurred beneath this area.

Design and Implementation of the Interactive Inversion Software for Focal Mechanism Solution CUI Ren-sheng, CHEN Yang, ZHAO Cui-ping, LUO Jun EARTHQUAKE    2023, 43 (3): 190-202.   DOI: 10.12196/j.issn.1000-3274.2023.03.014 Abstract （107）      PDF（pc） （4652KB）（114）       Knowledge map    In order to obtain reliable the source parameters quickly, such as focal mechanism solutions for mid-strong earthquakes, an interactive inversion software based on CAP method is designed and implemented. The software has a graphical interface to read the earthquake waveform from regional seismic network. Stations used for inversion are selected by user. Then the software can be used to automatically process the observed waveforms, calculate the theoretical Green's function and invert the focal mechanisms of the earthquakes. It is proved that the software is convenient, reliable and robust by testing multiple earthquakes with different tectonic environments, different magnitudes and different types. The software is easy to quickly obtain focal mechanism solutions of the intermediate or strong earthquake. It is significance to provide the solutions data for emergency response, and it is beneficial to the study on seismic source properties.

Analysis of Variation Characteristics of DF Microseisms Signals before the 2020 Changqing M4.1 Earthquake LI Hui-ling, ZHANG Ming, LIN Xiu-na, CHEN Hong-kai, WEI jin, YAN Ming-hao EARTHQUAKE    2023, 43 (3): 138-149.   DOI: 10.12196/j.issn.1000-3274.2023.03.010 Abstract （106）      PDF（pc） （4595KB）（102）       Knowledge map    Before an earthquake, the gravimeter may record high-frequency disturbance signals related to the source. On February 18, 2020, an M4.1 earthquake occurred in Changqing, Shandong Province. The observation data of PET gravimeter at Tai'an station, about 52 km away from the epicenter, showed energy enhancement and the vertical displacement of DF ground pulsation increased (0.13×10-6 m) since 5 days before the earthquake. In order to clarify the relationship between this phenomenon and the Changqing earthquake, time-frequency analysis in the 0.1~0.5 Hz frequency band is carried out to the gravity data in February 2020 and the vertical displacement of the DF pulsation signal is calculated. The results are synchronized with the global model of seismic background noise energy radiation (ASSM); After excluding the influence of typhoon, comparatively analyzing of the gravity data of Jiaxiang station and the vertical component acceleration data of JCZ-1 seismometer at Tai'an station, obtaining weather information and wave height data, the pulsation signal excited by the signal source from the wave is determined. The mean square deviation of the DF vertical displacement of the gravimeter in Tai'an station is used as the prediction index to test the R-value. The result shows that this phenomenon is not related to the 2020 Changqing M4.1 earthquake. The analysis methods and processes of gravity data change, as well as the methods and ideas for determining the signal source that causes data change in this paper, provide a reference for the anomaly identification and determination of gravimeter observation data, which can be applied to seismic analysis and prediction in related situations.

Visual Analysis Platform of Borehole Strain Data Based on B/S LI Fu-zhen, REN Tian-xiang, ZHANG Huai, SHI Yao-lin EARTHQUAKE    2023, 43 (1): 185-197.   DOI: 10.12196/j.issn.1000-3274.2023.01.014 Abstract （106）      PDF（pc） （4299KB）（62）       Knowledge map    With the accumulation of four-component borehole strain observation data and the increase of seismic stations, it is important to improve the efficiency of processing and analysis of these data. Due to the high resolution of borehole strain observation data in an ultra-wide frequency band, borehole strain observation data are significant for earthquake and earthquake prediction research. Using the normal stress petal diagram to display the change of in-situ stress, we can not only qualitatively analyze the relative in-situ stress change at the station, but also quantitatively read the normal stress observed in any direction at a certain time. In this paper, this method is combined with data visualization technology and chart data combined with map display as the main body of the platform builds a visualization analysis platform of four-component strain data based on B/S architecture. This platform can intuitively display the spatiotemporal variation law of in-situ stress recorded by the borehole strain gauge and realize the visual analysis and interaction of borehole strain data and shared access by multiple users.

The 10-WTGTP (10th Workshop on Tectonics and Geophysics in the east part of Tibetan Plateau) was held online in 2022 LIU Tong-zhen, XIA Xin-yu, ZHANG Huai, AI Yin-shuang, YANG Shu-xin, GAO Yuan EARTHQUAKE    2023, 43 (1): 198-200.   DOI: 10.12196/j.issn.1000-3274.2023.01.015 Abstract （105）      PDF（pc） （302KB）（50）       Knowledge map

3D Mesh for the Fault System in China Seismic Experimental Site ZHANG Rong-xin, XING Hui-lin, SHU Tao, LIU Jun-biao, GUO Zhi-wei, WANG Jian-chao, TAN Yu-yang EARTHQUAKE    2023, 43 (3): 18-33.   DOI: 10.12196/j.issn.1000-3274.2023.03.002 Abstract （100）      PDF（pc） （8747KB）（63）       Knowledge map    The Sichuan-Yunnan region is subjected to frequent earthquakes due to the collision of the Indian and Eurasian plates, rendering it a ideal experimental site for seismic research. This paper presents a rapid method for constructing a finite element mesh model with complex faults based on a geometric mesh model of the region, using the example of the geometry model of major faults in fault system of Sichuan-Yunnan region. The following research has been conducted: ① The Advancing Front Technique (AFT) has been improved to generate a three-dimensional triangle mesh based on the geometric model, and automatically identify areas that require local refinement and conduct mesh refinement. ② An algorithm for identifying the intersection lines of intersecting faults has been proposed, and it can recognize the intersection lines between different surfaces (including fault surfaces and study area's boundaries) based on the spatial geometric relationship between non-parametric surfaces. ③ The rapid method for constructing a finite element mesh model with complex faults based on a geometric mesh model of the region has been improved. First, the original fault model is manipulated using expansion and connection operations to enable it to represent the true shape of the fault geometrically. Subsequently, the boundary of the study area and the fault mesh are combine. The intersection lines between different fault planes or between fault planes and the study area's boundary are then identified. Then, using the improved advancing front technique, the fault surface is remesh with the intersection lines as constraints to repair the mesh topology and improve the mesh quality. Finally, a tetrahedral calculation mesh model containing faults is automatically generated using the newly generated triangular mesh of the fault surface as constraints. ④ The above method has been applied to the China seismic experimental site to construct a three-dimensional calculation mesh model containing the main fault system which lays the foundation for using finite element numerical simulations to study the seismic dynamics in the study area.

Characterstics of Tectonic Deformation before the 2021 Yangbi MS6.4 Earthquake in Yunnan ZOU Fang, MENG Guo-jie, SU Xiao-ning, WU Wei-wei, ZHAO Qian, SHE Ya-wen, Thant Myo EARTHQUAKE    2022, 42 (3): 21-36.   DOI: 10.12196/j.issn.1000-3274.2022.03.002 Abstract （99）      PDF（pc） （7867KB）（62）       Knowledge map    In May 2021, a series of moderate earthquakes occurred in Yangbi, Yunnan Province, which seriously threatened the safety of people’s lives and property. The epicenter of Yangbi MS6.4 earthquake is located near the Weixi—Qiaohou—Weishan fault in the South Yunnan block. The seismogenic fault is a newly discovered fault with a strike of 135°. Based on GPS observation data from 1998 to 2020, the long-term crustal movement velocity field in the study area is obtained, and the horizontal deformation background characteristics of the regional crust before these strong earthquakes in Yangbi are studied, as well as its relationship with the occurrence of earthquakes. Combined with the structural analysis, it is considered that the Yangbi earthquake occurred in the area where GPS horizontal velocity steeply change. Here the horizontal crustal movement was blocked and the strain accumulation is obvious with the high value area of surface strain rate and maximum shear strain rate. The seismogenic faults in this area are mainly affected by dextral shear and E-W extension.

Establishment of Three-Dimensional Model of Yishu Fault Zone Based on Magnetotelluric Profiles FU Jun-dong, XU Hong-tai, XIA Nuan, CHEN Ping, WANG Lei, XIONG Ren-wei EARTHQUAKE    2023, 43 (3): 34-49.   DOI: 10.12196/j.issn.1000-3274.2023.03.003 Abstract （95）      PDF（pc） （7658KB）（80）       Knowledge map    Based on the magnetotelluric profile data, combining with geological profiles, medium-depth seismic reflection exploration profiles, modern seismic catalogue, ALOS-dem data, satellite images and other data, the Shandong section of the Yishu fault zone is selected as the research area. The 3D model of the Yishu fault zone in the depth of 20 km in Shandong is established by using the three-dimensional modeling software Blender, and the modeling process of “satellite image—surface elevation model—shallow fault line—underground structure of the fault revealed by magnetotelluric exploration—underground fault plane—underground seismic ball—3D model”. The following conclusions are obtained: ① The Yishu fault zone shows a 3D structure of two grabens plus one horst from the surface to the underground as a whole; ② The main faults show the characteristics of segmental activity, with obvious differences in occurrence at different segments and complex fault contact relations; ③ Modern earthquakes are mainly distributed along the two faults of the eastern graben in the Yishu fault, with the characteristics of zonal and cluster distributions. The frequency of seismic activity in the strong activity section is obviously higher than that in the weak activity section. The establishment of the three-dimensional model of the Yishu fault zone provides a basis for discussing the influence relationship between earthquakes and active faults, studying the seismogenic mechanism of the Yishu fault zone and reproducing earthquake scenarios.

Application of Standard Annual Dynamic Curve Method in Radon Data Processing of Seismic Fluid Monitoring Station WANG Yang-hong, SU He-jun, ZHANG Hui, LI Chen-hua, ZHOU Hui-ling EARTHQUAKE    2023, 43 (1): 171-184.   DOI: 10.12196/j.issn.1000-3274.2023.01.013 Abstract （94）      PDF（pc） （5556KB）（52）       Knowledge map    Background information and precursor information are the main observation data of a station. It is a key link to improve the effectiveness of seismic activity monitoring and prediction through accurate identification and correct extraction of precursor information. In this paper, the standard-year dynamic curve morphological analysis method was used to detrend the daily water (gas) radon value of 8 underground fluid stations in Gansu Province. The smoothing of the “forward slip” of the years of daily value was carried out and the mean square error as the upper and lower limits of the smooth curve was calculated. The abnormal values exceeding the upper and lower limits were used as anomalous information for earthquake case statistics, so as to gain earthquake reflecting ability and spatial response characteristics of the precursory anomalies of water (gas) radon at 8 underground fluid stations. It is concluded from the study that the standard annual dynamic curve analysis method could be an effective method to identify the precursory short-impending anomaly information of groundwater (gas) radon, and expected to play an important technical support role in the precursory data analysis and abnormal processing of underground fluids.

Study on Quaternary Activities Characteristics of the Mengshan Piedmont Fault FENG Jian-guo, ZHAO Yao, WANG Ji-qiang, GAO Zong-jun, WANG Hua-lin, GE Fu-gang EARTHQUAKE    2023, 43 (3): 66-76.   DOI: 10.12196/j.issn.1000-3274.2023.03.005 Abstract （92）      PDF（pc） （4079KB）（102）       Knowledge map    The Mengshan piedmont fault is a relatively active NW trending fault in the western Shandong block. In order to study its Quaternary activity characteristics, the latest activity and deep structure of the Mengshan piedmont fault have been preliminarily studied by using field observation, trench profile analysis, geochronology measurement and other methods in combination with gravity anomaly characteristics, which is of great significance for evaluating the seismic risk of the Mengshan piedmont fault. The results show that: ① Since the Quaternary, the Mengshan piedmont fault is mainly characterized by sinistral strike-slip and normal fault movement. The fault, bounded by Yujiazhuang Village, is divided into east and west sections. The western section has not been active since the Quaternary, while the eastern section has been active mainly in the late Pleistocene. ② The Mengshan Piedmont fault cuts deep to the middle and lower crust, which is a deep major fault. ③ There may have been two paleoseismic events in the Mengshan Piedmont fault since the late Pleistocene, (44.1±3.4)~(24.3±1.2) ka and (22.7±1.8)~(6.2±0.5) ka, respectively. ④ There have been many M≈5 earthquakes the fault zone, which has the potential risk of triggering moderate and strong earthquakes. It is suggested to strengthen the in-depth study of the fault in the future.

Seismic Activity, Focal Mechanism Solution and Stress Field in the Jinping Ⅰ Reservoir and Its Surrounding Area before and after Impoundment CHEN Han-lin, LIU Rui-feng, WANG Qin-cai EARTHQUAKE    2023, 43 (3): 120-137.   DOI: 10.12196/j.issn.1000-3274.2023.03.009 Abstract （92）      PDF（pc） （5037KB）（86）       Knowledge map    In this paper, we studied seismicity and relocated earthquakes with ML≥0.5 occurring in the Jinping reservoir and its surrounding area before and after the impoundment. Then we inversed the mechanism solutions of 71 ML≥3.0 earthquakes occurred the stress field before and after impoundment. The initial response time of the earthquake Jinping Level Ⅰ Reservoir in the was relatively long, which should be related to the lack of coverage of the flooding area near the earthquake swarm. After expanding to Hulugou, seismicity increases sharply, the changes of seismicity in the following stages have good relationship with the impoundment process. After the impoundment, a large number of earthquakes concentrated near Hulugou in Tibetan Autonomous County of Muli, with focal depths ranging from 6 to 14 km, which became shallower compared to the focal depths before the impoundment. Except for the results of focal mechanism solutions in the Hulugou, P-axis and T-axis distribution, regional stress field except for Hulugou are consistent with previous research results. The focal mechanisms of the earthquake near Hulugou are mostly strike type, with the P-axis mainly in the NS and NNW-SSE directions, and the T-axis mainly in the EW and NEE-SWW directions. The maximum and minimum principal stress axes of the regional stress field are nearly horizontal, and the intermediate stress axis is nearly vertical, the R-value is 0.5, different from other regions. We infer that their mechanisms should be influenced by pore pressure diffusion and infiltration weakening.

Application of Logic Tree in Seismic Risk Analysis of Liaoning Province WANG Yan, SHAO Yuan-yuan, ZHANG Bo, GUO Xiao-yan, ZHAI Li-na, YANG Shi-chao EARTHQUAKE    2022, 42 (3): 111-123.   DOI: 10.12196/j.issn.1000-3274.2022.03.008 Abstract （87）      PDF（pc） （3218KB）（71）       Knowledge map    The main basis of earthquake prediction research is the abnormal changes of various seismic information observed before the earthquake. The more abnormal changes, the more complete the available information for seismic risk research. However, more and more different anomalies are inconsistent with the seismic risk judgment results, increasing the complexity of comprehensive analysis. In this paper, taking Liaoning region as the research area, the logic tree method is introduced, and the seismic risk logic tree model is established according to the long, medium, short and imminent time scales of the earthquake preparation process. Then we scan the whole region to obtain the relative probability distribution of seismic risk in Liaoning and the distribution of seismic risk index in Liaoning. The introduction of logic tree method quantifies the comprehensive influence of anomalies on regional seismic risk, and simplifies the analysis process. The Xiuyan M5.4 earthquake in 1999 and the Dengta M5.1 earthquake in 2013 were analyzed as typical examples, the results showed that if we could collect more earthquake anomalies, and the influence time of the anomalies were more accurate, then we would get more accurate earthquake prediction results.

Study on Earthquake Forecast in the North-South Seismic Belt by Pattern Informatics Method TIAN Wei-xi, ZHANG Yong-xian EARTHQUAKE    2023, 43 (3): 159-177.   DOI: 10.12196/j.issn.1000-3274.2023.03.012 Abstract （86）      PDF（pc） （4535KB）（100）       Knowledge map    We study the prediction efficiency of Pattern Informatics method (PI) in different areas of the North-South Seismic Belt in this paper. The earthquake catalogue since 1970 is taken from the China Earthquake Networks Center. Both the change interval and forecast interval are fixed as 5 years and the grid size is taken as 1°×1°. We have the retrospective forecasting for 6 earthquakes above MS6.0 in the study region since 2017. The forecasting efficiency of PI is tested by ROC (Receiver Operating Characteristic) method. The results show that: ① The prediction efficiency of the south, middle and north sections of the North-South Seismic Belt shows a trend of decreasing gradually, but the change is small. This indicates that the prediction performance of PI method is affected by the intensity of regional seismicity to a certain extent. ② The prediction efficiency of piecewise calculation for the North-South Seismic Belt is better than that of the whole calculation for the North-South Seismic Belt. In terms of prediction efficiency, the north and middle sections of the North-South Seismic Belt are the best, the south, middle and north sections are the second, the middle and south sections are relatively low, and the North-South Seismic Belt as a whole is the lowest. The analysis shows that the calculation process of PI method involves the normalization of seismicity, so PI prediction performance is better for areas with similar seismicity. Hot spots generated by PI in regions with different seismicity are mainly generated in areas with high seismicity and the prediction efficiency is low. Therefore, regional division of the North-South Seismic Belt by seismicity can improve the prediction efficiency. ③ There are persistent high probability “hot spots” in Yongde-Lushui area in southwest Yunnan and near the southern section of Longmenshan Fault. These areas should be concerned for earthquakes with MS≥6 in the next five years.

Diffusion of Helium in Minerals and Its Application Prospects in Seismic Research WANG Ling-ling, LIU Hong, SUN Feng-xia, LI Yi-shan, LIU Lei, ZHOU Xiao-cheng EARTHQUAKE    2022, 42 (3): 165-179.   DOI: 10.12196/j.issn.1000-3274.2022.03.012 Abstract （84）      PDF（pc） （2612KB）（52）       Knowledge map    Studying the diffusion characteristics and closure temperature of He in the surface and deep earth minerals is of great significance for understanding the information of earthquake precursors and tectonic activity. It is also important for understanding the process and law of mineralization. The article summarizes research results of the diffusion characteristics of He in some typical minerals. They mainly include: ① The diffusion of He diffusion in zircon; ② The diffusion of He in apatite; ③ The diffusion of He in quartz and coesite; ④ The diffusion of He in carbonate; ⑤ The diffusion of He in hydrated minerals such as amphibole. In order to analyze the relationship between the diffusion and escaping behavior of He from minerals and the anomaly of He concentration in the process of seismicity, the future research direction is proposed.

Study on Stress Field and Seismogenic Fault in Menyuan Area YANG Cheng, WAN Yong-ge EARTHQUAKE    2023, 43 (3): 77-90.   DOI: 10.12196/j.issn.1000-3274.2023.03.006 Abstract （84）      PDF（pc） （3714KB）（111）       Knowledge map    The determination of stress field and fault geometry is an important basis for earthquake dynamics. In order to determine the stress field and fault geometry in Mengyuan region, where occurred an MS6.9 earthquake on Jan 8, 2022, by using focal mechanism, firstly, focal mechanisms were collected from 1927 to 2022 in Menyuan region of Qinghai Province. For multiple focal mechanisms of the same earthquake, the central focal mechanism solution was as the focal mechanism of the earthquake, and used as the basic data for solving the stress field and fault geometry. Then cluster analysis was carried out with the focal mechanism node data, to obtain the possible fault plane shape of the seismic sequence, and solve the tectonic stress field in the study area. Finally, the slip angle was estimated by projecting the tectonic stress field onto the fault plane, and the relationship between the stress field and the seismogenic fault was simulated. The results showed that the overall strike and dip angle of the Mengyuan earthquake sequence are 103.19° and 72.44°, respectively, which were consistent with the azimuth of the Lenglongling fault from field geological survey. The azimuth and plunge of the compressional, tensional axes of the tectonic stress field in the study region were 242.37°, 0.93°, 334.79°, and 68.98°, respectively. It could be explained that the NE spreading in northeastern margin of the Tibet block was blocked by the stable Alxa Block, resulting in a thrust and strike-slip fault system in the study region. By projecting the stress field onto the fault plane of the earthquake sequence, the slip angle of the fault was estimated as 50.68°, the relative shear stress and normal stress were 0.822 and -0.077, respectively, which indicated that the Menyuan area had a large shear stress and a weak compression state on the steeper NWW—SEE fault under the NE-trending compressive stress of the Tibet and Alxa Massifs.

Tomographic Study on the Velocity Structures and P-wave Azimuthal Anisotropy of the 2019 Changning MS6.0 Earthquake Surrounding Area YANG Wei-jia, ZHOU Yan-jie, JIANG En-yuan, SHI Yu-tao, MA Xiao, HE Xi-jun, HUANG Xue-yuan EARTHQUAKE    2023, 43 (4): 1-20.   DOI: 10.12196/j.issn.1000-3274.2023.04.001 Abstract （81）      PDF（pc） （16915KB）（79）       Knowledge map    In this paper, the eikonal equation-based seismic tomography method was used to invert the velocity structure of the source and surrounding area of the Changning MS6.0 earthquake in 2019. High-resolution 3-D P- and S-wave velocity as well as the P-wave azimuthal anisotropy models are obtained, and Poisson's ratio of several typical profiles is analyzed. The results show that the azimuthal anisotropy significantly affects the P-wave travel times, revealing strong crustal heterogeneities in the study area. Some low-velocity anomalies have good spatial correspondence with industrial activities fields, which may indicate the properties of upper crustal media have been affected by the shale gas hydraulic fracturing, fluid injection in salt minefields, and/or disposal of wastewater in natural gas fields. The Changning MS6.0 earthquake may be directly induced by salt mining by water injection, and the velocity anomaly structure caused by industrial activities may have a sustained effect on the occurrence of earthquakes in the region. The P-wave azimuthal anisotropy in this region may be dominated by the plate motion and principal compressive stress. The anisotropy in the shallow depth of the Changning earthquake source region shows near EW direction, which is consistent with the direction of regional principal compressive stress. These results provide new insight into the fine crustal structure, deep material movement, and dynamic mechanism in the southeastern margin of the Sichuan Basin.

Research Progress of Hydraulic Fracturing Induced Earthquake CHEN Qiu-yu, ZHANG Xiao-dong, ZHAO Cui-ping EARTHQUAKE    2023, 43 (4): 215-227.   DOI: 10.12196/j.issn.1000-3274.2023.04.014 Abstract （80）      PDF（pc） （1104KB）（69）       Knowledge map    In recent years, the popularity of hydraulic fracturing technology inducing seismicity it has attracted wide attention all over the world. Since the comprehensive promotion of hydraulic fracturing technology in 2015, as one of the main areas of shale gas exploitation in China, Sichuan Basin has an increasing trend in the frequency and magnitude of seismic activity. We collect the data of global earthquakes induced hydraulic fracturing, especially in Sichuan Basin, to expound the seismicity characteristics, inducing mechanism, earthquake monitoring, risk mitigation, disaster prediction of induced earthquakes, which have certain value of reference to the comprehensive understanding of hydraulic fracturing induced earthquakes.

Distribution Characteristics and Genetic Analysis of Mingtiaogang Fractures in Yuncheng Basin GUO Chun-shan, LI Wen-qiao, XU Yue-ren, YAN Xiao-bing EARTHQUAKE    2023, 43 (4): 50-66.   DOI: 10.12196/j.issn.1000-3274.2023.04.004 Abstract （77）      PDF（pc） （17097KB）（98）       Knowledge map    The Mingtiaogang fracture is located on the southeast side of the Mingtiaogang land barrier in the northeastern part of the Yuncheng Basin, causing the cracking and deformation of infrastructure along the route, including the cracking of house walls, road cracking, farmland destruction, etc., which has caused a serious impact on agricultural production and people's life along the route. Through a large number of field geological surveys, surface mapping and data collection, this paper obtains the spatial distribution and dislocation data of cracks in the ground. The cracks in the ground extend more than 15 km, striking 58°, with a maximum depth of 2.5 m, a maximum width of 5 m, and a vertical sliding rate of 6.25～8 mm/a. It is determined that the cracks in Mingtiaogang belong to the comprehensive cause of tectonic and non-tectural movements. The ground subsidence caused by super-exploitation of groundwater is its fundamental cause. Due to the different sedimentary thicknesses on both sides of the fault and the settlement difference caused by groundwater collection, the fault of the southern edge of the Mingtiaogang controlles the fracture distribution , while rainfall and loess wet subsidence have a tendency to expand on the fracture formation.

Development and Realization of Earthquake Consultation Technology System LIU Qi, MA Ben, SUN Shao-bo, ZHANG Xiu-ping EARTHQUAKE    2022, 42 (3): 152-164.   DOI: 10.12196/j.issn.1000-3274.2022.03.011 Abstract （77）      PDF（pc） （5500KB）（54）       Knowledge map    To alleviate the increasingly serious contradiction between the urgency of consultation business needs and the backward working mode, based on the DatistEQ development platform and the earthquake consultation system cloud management center, the earthquake consultation technology system of the Institute of Earthquake Forecasting was constructed and deployed. The system is currently mainly composed of two subsystems, the “Earthquake Emergency Output System of M5 earthquakes in China” and the “Earthquake Emergency Output System of M7 earthquakes in the world”. Based on 4 main output and integration modes, the collection of earthquake emergency consultation products has been realized. Pushing products with different time is carried out through various forms such as WeChat enterprise account/enterprise WeChat, WeChat group, mailbox, B/S website, etc. Based on two modes of automatic triggering and manual triggering, both business automation and output flexibility are taken into consideration. Through the local backup system and regular monitoring of the server status, the continuous and stable consultation output is ensured. Relevant experience and understanding can play a certain reference role for the construction of consultation technology systems of other units, and jointly promote the transformation and upgrading of earthquake consultation business.

Explanation for the Anomalies of the Ground Resistivity in NS Direction at Hefei Deformation Station YU Lei, CHEN Jun, HE Kang, LIU Ze-min, LI Zhe-jun EARTHQUAKE    2022, 42 (3): 180-191.   DOI: 10.12196/j.issn.1000-3274.2022.03.013 Abstract （74）      PDF（pc） （1781KB）（54）       Knowledge map    The earth resistivity always shows reverse change in NS direction and EW direction at Hefei deformation station, however the data of the two directions showed positive change from October 2018 to February 2019. After checking, it is found that there is a reservoir between the NS power supply level and the measuring pole, and in October 2018 the water level of the reservoir was significantly reduced due to pumping. At this time, the resistivity at NS direction did not increase but decrease that formed a paradox. In this paper, the three-dimensional influence coefficient is calculated by using finite element numerical analysis method. The results show that there is a negative region between the supply electrode and the measuring electrode, and a semi-ellipsoid region along the measuring profile. The closer it is to the electrode, the longer the absolute value of influence coefficient becomes. It is concluded that the abnormal change in NS resistivity is caused by the pumping of water from the reservoir, and the calculated results are consistent to the observed data. This result provides reference for solving similar problems in the future.