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    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
    Abstract213)      PDF(pc) (2951KB)(62)      
    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。
    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
    Abstract145)      PDF(pc) (7771KB)(71)      
    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.
    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
    Abstract138)      PDF(pc) (8351KB)(72)      
    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
    Abstract128)      PDF(pc) (7964KB)(109)      
    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.
    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
    Abstract104)      PDF(pc) (3906KB)(150)      
    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.
    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
    Abstract102)      PDF(pc) (4595KB)(96)      
    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.
    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
    Abstract98)      PDF(pc) (4652KB)(107)      
    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.
    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
    Abstract94)      PDF(pc) (8747KB)(61)      
    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.
    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
    Abstract86)      PDF(pc) (7658KB)(70)      
    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.
    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
    Abstract80)      PDF(pc) (4079KB)(94)      
    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.
    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
    Abstract80)      PDF(pc) (3714KB)(93)      
    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.
    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
    Abstract78)      PDF(pc) (5037KB)(77)      
    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.
    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
    Abstract77)      PDF(pc) (16915KB)(75)      
    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.
    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
    Abstract77)      PDF(pc) (4535KB)(83)      
    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.
    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
    Abstract70)      PDF(pc) (17097KB)(90)      
    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.
    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
    Abstract63)      PDF(pc) (1104KB)(58)      
    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.
    Study on the Mode-kissing of Surface Waves Based on the Theory of the Mode and Generalized Ray
    WANG Shao-tong, LU Lai-yu
    EARTHQUAKE    2023, 43 (4): 76-100.   DOI: 10.12196/j.issn.1000-3274.2023.04.006
    Abstract61)      PDF(pc) (8790KB)(58)      
    In near-surface surface wave exploration, especially in typical sedimentary basins, mode-kissing of the fundamental and first-order modes is often observed for the dispersion image in the frequency-phase velocity domain. In the mode theory of waves, surface wave mode in the frequency domain is associated with a series of poles determined by the dispersion equation. In the generalized ray theory, the multipath in the spatial-temporal domain gives rise to the multimode in the frequency domain. Combined with the generalized theory and the mode theory, the influence of the $\bar{P}$ pole and the $\bar{S}$ pole on dispersion curves is studied to explain the mode-kissing phenomenon. For a two-layer model, the characteristics of the dispersion curves, eigen displacement, and polarization of the particle, which varies with the moving of $\bar{P}$ pole in the complex ray parameter plane, are studied by changing the S wave velocity β(2) of the bottom half space, both for the fundamental and the first overtone. It is found that mode-kissing appears when the $\bar{P}$ pole passes through the branch point 1/β(2) in the complex ray parameter plane and just enter the area belongs to the normal mode. The particle motion of the first leaky mode corresponding to the $\bar{P}$ pole is a prograde ellipse, but the eigen displacement shows the characteristic of the classical surface wave, i.e., the displacement mainly concentrates near the surface and decays rapidly with depth.
    Spectral Characteristics before 2021 Maduo MS7.4 Earthquake and 2010 Yushu MS7.1 Earthquake
    YU Na, SUN Xi-hao, ZHANG Xiao-qing
    EARTHQUAKE    2023, 43 (3): 150-158.   DOI: 10.12196/j.issn.1000-3274.2023.03.011
    Abstract60)      PDF(pc) (3621KB)(63)      
    In order to further test and improve the judgment basis for identifying foreshocks through the characteristics of “narrow frequency band and low-frequency migration”, this paper compares and analyzes the FFT spectra of the Maduo MS4.2 earthquake in Qinghai on December 24, 2020, and the Yushu MS4.7 earthquake in Yushu on April 14, 2010. based on the waveform data recorded by digital seismic networks in Qinghai, Gansu, and other regions. The results show that the frequency band of Maduo MS4.2 earthquake spectrum is wide, the dominant frequency band is 0~5.0 Hz. The frequency band of the Yushu MS4.7 earthquake narrowed and shifted to the low-frequency end, the dominant frequency band of 0~1.5 Hz. The comparative analysis shows that the “frequency band narrows and shifts to low frequency” phenomenon is effective for direct foreshock identification. In the future, it is necessary to focus on the possibility of strong earthquakes occurring near the source area in the short term (1~3 months) after the frequency spectrum shift of small and medium earthquakes occurring.
    LSTM Neural Network for Automatic P Phase Picking
    WU Wei-zhi, WANG Xiao-li, HE Ze-ping
    EARTHQUAKE    2023, 43 (4): 67-75.   DOI: 10.12196/j.issn.1000-3274.2023.04.005
    Abstract60)      PDF(pc) (1329KB)(71)      
    Picking up the arrival time of seismic phases is one of the fundamental problems of seismology. This study introduces a method based on LSTM neural network for automatic P phase picking. We transformed the arrival time problem into the probability problem of time redefined labeling, and a 4-layer neural network was built and trained on the North Korean nuclear earthquake vertical waveforms. The P phase arrival time of subsequent events were picked up accurately and effectively. The method shows a certain adaptability with ambient noise. Random input samples test shows that the input waveform data should be better with longer than 10 s after the P phase to get stable results. As an artificial intelligence method, LSTM neural network provides a new solution for seismic phase picking-up.
    The Seismogenic Background of the 2020 Tangshan M5.1 Earthquake
    TANG Jie, ZHANG Su-xin, FENG Xiang-dong, SUN Li-na, WANG Xiao-shan, BIAN Qing-kai
    EARTHQUAKE    2023, 43 (4): 37-49.   DOI: 10.12196/j.issn.1000-3274.2023.04.003
    Abstract58)      PDF(pc) (4455KB)(67)      
    More than 40 years after the 1976 Tangshan earthquake of M7.8, an M5.1 earthquake still occurred on July 12, 2020 in Guye located at the northeast end of Tangshan fault. In this paper, the multiple seismogenic background of this earthquake is analyzed by combining the tectonic background, the space-time image of many small earthquakes, the result of focal mechanism solution of many earthquakes, on-site investigation and other data as well as previous research results. The results show that the seismic fault is the Mozhouyu fault which is conjugated with Tangshan fault zone, and there still exists a certain risk for future earthquake occurrence in this area. Through this study, a new understanding of seismogenic tectonic background in the old Tangshan seismic area has been obtained.
    Study on Coseismic Landslides Triggered by Ludian MS6.5 Earthquake, Yunnan Province, on August 3rd, 2014, Using Remote Sensing Images
    XIAO Jin-yu, XU Yue-ren, LIU Lei, ZHANG Wei-heng, LI Wen-qiao, DU Peng
    EARTHQUAKE    2023, 43 (4): 101-118.   DOI: 10.12196/j.issn.1000-3274.2023.04.007
    Abstract55)      PDF(pc) (10219KB)(53)      
    The types of coseismic landslides in different geomorphological environments have great differences. Confirming their types is of great significance for understanding the characteristics of disasters. Using multitemporal highspatial resolution satellite and aerial images, combined with comprehensive remote sensing interpretation and field investigation methods, retrospectively study the temporal and spatial distribution characteristics of landslides triggered by the typical moderate to strong earthquake in western China, and have a good understanding of the occurrence and evolution characteristics of coseismic secondary disasters. This paper focused on the case of “moderate size earthquake with severe catastrophe” of the August 3rd, 2014 Ludian MS6.5 earthquake in Yunnan Province which triggering coseismic landslides. The research shows that ① The number of triggeredlandslides database is 6 209, with a total area of 9.72 km2, of which 10 landslides have areas of great than 70 000 m2 caused major disasters, such as Niulanjiang River dammed lakes and blocking lifelines; ② Most of the extracted triggered landslides are belong to bedrock collapses, with small provenance areas, narrow and long circulation areas, and accumulation areas in the form of piles of rocks at the foot of the slope, which have the characteristics of relative bigger affected area but smaller volumes; ③ The coseismic landslides triggered by the LudianMS6.5 earthquake are consistent with the characteristics of the database of coseismic landslides in mountains and valleys triggered by other strong earthquakes in western China.
    Rayleigh Wave Dispersion Characteristics Based on the Observations from Seismometer and Collocated Four-Gauge Borehole Strainmeter
    WANG Xiao-lei, XUE Bing, CUI Ren-sheng, ZHU Xiao-yi, GAO Shang-hua, ZHAO Shuai-bo, ZHANG Bing
    EARTHQUAKE    2023, 43 (4): 21-36.   DOI: 10.12196/j.issn.1000-3274.2023.04.002
    Abstract53)      PDF(pc) (6761KB)(54)      
    As one of the important parts of the construction of the China Seismic Experimental Site, the borehole seismic observation system construction project has built an observation array of borehole near the Anninghe-Zemuhe fault, consisted of 10 borehole with a depth of 300 meters and 3 borehole with a depth of 1000 meters. By integrating the broadband seismometer and the Four-Gauge Borehole Strainmeter (FGBS), the co-point observation of seismic and strain is formed. The sampling rate of both FGBS and seismometers is 100 Hz, which is conducive to obtain high-quality seismic and strain seismic wave data of teleseism, regional earthquakes, and near-field microseisms. In this paper, based on the data of 300-meter borehole Tuowu, one of the earliest comprehensive seismic observation boreholes, we try to use the amplitude information of seismic waves and strain seismic waves, combining the theory of single-site estimation of phase velocity, to obtain the local Rayleigh wave phase velocity dispersion curve in the period of 20~125 s.
    Research on the Three-Dimensional Deformation along the Maqin-Maqu Section of the East Kunlun Fault zone from InSAR
    ZHANG Xia, DONG Yan-fang, HONG Shun-ying
    EARTHQUAKE    2023, 43 (4): 169-184.   DOI: 10.12196/j.issn.1000-3274.2023.04.011
    Abstract50)      PDF(pc) (7905KB)(45)      
    The East Kunlun Fault (EKF) is one of the most active left-lateral strike-slip faults located in the Qinghai-Tibet Plateau, and it is the northern boundary of the Bayan Har Block. The Maqin-Maqu segment of the East Kunlun Fault is a MW5.0 earthquake gap in the past 400 years. Based on PS-InSAR technology, we use Sentinel-1A/B Ascending and Descending SAR data from European Space Agency to obtain the LOS deformation velocity of the Maqin-Maqu segment. Combined with GNSS data, the three-dimensional velocity and fault-parallel velocity under the Eurasian reference frame are derived. Then, the Markov chain Monte Carlo method is used to invert the slipping rate and locking depth of the Maqin-Maqu segment and its surrounding faults. The results indicate that no obvious creep has been observed in the Maqin Maqu section. From west (Animaqing Mountain, 300 km away from the end of the East Kunlun fault) to east, the slipping rate gradually decreases from 4.7 mm/a to 2.3 mm/a. The Maqin-Maqu segment has a locking depth more than 10 km, resulting in sustained strain accumulation and closing to the recurrence. The cumulative seismic moments of both Maqin and Maqu segments reach ~1.00×1020 N·m, equalling to an MW7.3 earthquake. If the two segments rupture simultaneously, the released seismic moment energy is equivalent to an MW7.5 earthquake. The seismic risk of the Maqin-Maqu segment is worth poajing attention to.
    Population Thermal Analysis of Luding M6.8 Earthquake Based on Mobile Phone Location
    YIN Jing-fei, LI Dong-ping, XIAO Ben-fu, MIAO Xin-hui, SHEN Wei-yong, YAO Di
    EARTHQUAKE    2023, 43 (4): 185-199.   DOI: 10.12196/j.issn.1000-3274.2023.04.012
    Abstract48)      PDF(pc) (7648KB)(69)      
    After Luding M6.8 earthquake on September 5, 2022, to understand the population distribution in the disaster area and determine the scope of the megaseismic region, we collect mobile phone location data for different periods in the disaster area using the third-party mobile push service, and analyse the population distribution before the earthquake and the population thermal changes after the earthquake by using kernel density space processing methods. The results show that after the earthquake the population heat is weakened in the Meizoseismal area, but enhanced in the towns far from the epicenter. We can fit the seismic influence field by interpolating the change rate of quantity of the mobile phones. The population thermal data can provide an effective way to quickly obtain population dynamics in disaster areas and provide data support for fast assessment of seismic disaster.
    Seismic Magnetic Effects in the Northeastern Margin of the Qinghai-Tibet Plateau Based on Hurst Exponent
    SU Shu-juan, YANG Yan-ming, ZOU Chun-hong, SUN Hao, ZHANG Yao-wen, ZHANG Zhen-han, JIA Zhen, WU Yang
    EARTHQUAKE    2023, 43 (4): 119-134.   DOI: 10.12196/j.issn.1000-3274.2023.04.008
    Abstract45)      PDF(pc) (3836KB)(44)      
    Geomagnetic Z-component observations between 2012 and 2022 from 7 geomagnetic stations in the northeast of the Qinghai-Tibet Plateau, together with four seismic events, were selected to analyze the relationships between Hurst Exponent (H) values and seismic activities. Rescaled range analysis (R/S) and least square method (LSM) were used to calculate the Hurst Exponent (H) values. The results show that: ① H values of the geomagnetic Z-component from 7 geomagnetic stations located in the northeast of the Qinghai-Tibet Plateau, are ranged from 0.5 to 1.0 during the past 10 years, manifesting the characteristics of long-range correlation and persistence, which can be used to forecast the variation trends in the future. ② H values at 7 geomagnetic stations all decreased rapidly 1~3 months before the 4 earthquakes, till to below 0.5, and the deviation from the normal geomagnetic observations (0.5<H<1.0) indicates the occurrence of the geomagnetic anomalies. Epicenter distance and earthquake magnitude affect the occurrence probabilities of seismic-magnetic effects. The larger the magnitude and the smaller the epicentral distance are, the more obvious the seismomagnetic effects of the Hurst Exponent (H) values are. ③ The anti-persistence of the H may indicate the migration of deep crust-mantle heat flow. The upwelling of deep heat flow within the secondary plate of the Qinghai-Tibet Plateau, the lateral migration from the hinterland of the plateau to the periphery, as well as the existence of mantle heat uplift in Tianshui area, provide reference for exploring the seismogenic mechanism inside and around the northeastern margin of the Qinghai-Tibet Plateau block. The data analysis based on H can give more chance to capture and interpret seismomagnetic anomalies, supplement the research practice of earthquake cases, and explore the relationships between geomagnetic variations and seismic activities.
    Research Progress and Prospects of Coastal Earthquake Anomalies Based on Remote Sensing Technology
    ZHANG Lu, JIANG Meng, JING Feng
    EARTHQUAKE    2023, 43 (4): 200-214.   DOI: 10.12196/j.issn.1000-3274.2023.04.013
    Abstract44)      PDF(pc) (1567KB)(39)      
    During the seismogenic stage of a strong earthquake, the geophysical and geochemical changes in the tectonic plate and fault zone can propagate to the earth's surface and atmosphere through the medium, which can be observed by sensors aboard on satellite in the form of electromagnetic waves. During the past three decades, many geophysical and geochemical anomalies before continental earthquakes have been extracted and analyzed using satellite data. But less studies have been conducted on coastal earthquakes. Combined with the visualization analysis provided by the software named CiteSpace, the present paper comprehensively reviews the anomalies associated with coastal earthquakes based on remote sensing observation. By summarizing the variation characteristics of oceanic and atmospheric parameters related to coastal earthquakes, we discussed the key issues restricting the application of remote sensing technology in the research related to coastal earthquakes anomalies at present. Finally, combined with the analysis of problems and challenges in this field, the trend of coastal anomalies observation using remote sensing data is prospected, which provides an important support for the construction of comprehensive seismic multi-geosphere coupling model that includes both continental and oceanic earthquakes.
    The 11-WTGTP (11st-Workshop on Tectonics and Geophysics in the east part of Tibetan Plateau) was held in 2023 in Anqing, Anhui Province
    Yang Yi-wen, Naren Gerile, Xu Yi-xian, Ai Yin-shuang, Gao Yuan
    EARTHQUAKE    2023, 43 (4): 228-230.   DOI: 10.12196/j.issn.1000-3274.2023.04.015
    Abstract43)      PDF(pc) (382KB)(56)      
    EARTHQUAKE   
    Accepted: 03 January 2024

    Analysis on Variation of Geoelectric Field before MS5.5 Earthquake in Aksai County, Jiuquan in 2021
    XIN Jian-cun, FANG Wei, YANG Yi-hai, LI Na, YAN Wen-hua, FENG Hong-wu
    EARTHQUAKE    2023, 43 (4): 153-168.   DOI: 10.12196/j.issn.1000-3274.2023.04.010
    Abstract39)      PDF(pc) (5448KB)(37)      
    An MS5.5 earthquake occurred in Aksai County, Jiuquan on August 26, 2021. Based on the 2020—2021 observation data of 6 geoelectric field observation stations within a range of 500 km from the epicenter, a geoelectric field rock fissure water (charge) seepage (movement) model was used to calculate the dominant azimuth angle of the geoelectric field observation station. Combined with the focal mechanism and fixedpoint deformation observation data at Anxi station, we concluded that: ① The dominant azimuth angles showed abnormal changes at Shandan, Gaotai, Baishui River, which started in May 2021 and showed a certain degree of synchronicity. There was no significant abnormal change in the dominant azimuth angles at Guazhou, Dulan, and Jiayuguan. ② The daily average values of the Anxi Station's extensometer, vertical pendulum, comparing with Guazhou Station's geoelectric field that were approximately 12 km apart, showed nearly synchronous trend changes, acceleration, jumps, and other abnormal changes from April to July 2021, which indicated the correlation between different physical parameters. The application of geoelectric field and fixed point deformation observation data, through comprehensive analysis and mutual confirmation, we determined the changes in regional stress state, which provide ideas for exploring the application of different physical parameter anomaly evolution in data reliability analysis and earthquake prediction.
    EARTHQUAKE   
    Accepted: 03 January 2024
    Online available: 03 January 2024

    Study on Statistical Characterization of the Frequency Correlation of Seismic Anomalies in Geoelectric Fields
    FU A-long, AN Zhang-hui, FAN Ying-ying, YUAN Li-hua, HOU Ze-yu
    EARTHQUAKE    2023, 43 (4): 135-152.   DOI: 10.12196/j.issn.1000-3274.2023.04.009
    Abstract33)      PDF(pc) (4464KB)(49)      
    During earthquake preparation and occurrence, there have been relevant reports of abnormal phenomena in the geoelectric field at different frequencies. However, the statistical characteristics of the correlation between the different frequency components of the geoelectric field and the magnitude of earthquakes are still unclear. In this paper, we proposed to use the wavelet transform method to decompose the 12-year data of the geoelectric field in Pingliang station in Gansu Province, Hetian station and Wushi station in Xinjiang, China into different periodic components, such as 24 h, 12 h, 8 h, and 6 h, and then use the shifting correlation method to calculate and analyze the statistical characteristics of the correlation between each component and the magnitude of seismic events within a certain epicentral distance around the station. The results show that the high-frequency components (4 h and 6 h, etc.) of the geoelectric field show correlation anomalies with seismic events of two equivalent magnitude sequences, but the low-frequency components (24 h and 12 h) show correlation anomalies only with seismic events of larger magnitude sequences. Temporally, the correlation anomalies generally appear about 55, 20, or 10 days before the earthquake. This correlation between the frequency of the geoelectric field and the magnitude of earthquakes may be caused by the coupling between the seismogenic fault and tidal action. When the measurement channel of the geoelectric field is consistent with the fault orientation, it is easier to observe seismic anomalies, which may be a specific expression of the selective characteristics of the geoelectric field due to the tectonic rupture in the survey area. In addition, the occurrence time of correlation anomalies is not the same for each station, which may be related to the geological structure and geodynamic environment of the survey area.
    Preliminary Investigation and Analysis of Seismic Geological Hazards in Qinghai Disaster Area Induced By the 2023 MS6.2 Jishishan Earthquake
    YANG Chuan-cheng, LI Zhi-min, XIONG Ren-wei, GAI Hai-long
    EARTHQUAKE    2024, 44 (1): 216-225.   DOI: 10.12196/j.issn.1000-3274.2024.01.020
    Abstract33)      PDF(pc) (9873KB)(21)      
    At 23:59 Beijing Time on December 18, 2023, an MS6.2 earthquake occurred in Jishishan County, Gansu Province (35.70°N, 102.79 °E). Dahejia Town of Jishishan County was the macro epicenter of the earthquake, and the earthquake intensity was Ⅷ (8 degrees). Based on the preliminary field investigation of Qinghai area of Jishishan MS6.2 earthquake on December 18, 2023, geological hazards are found in many places. The distribution of earthquake intensity, types and characteristics of seismic geological hazards are introduced. The characteristics and effects of the earthquake hazards are analyzed and discussed.
    Geomorphic Index and Activity Characteristics of the Mid-Segment of Jiali Fault
    HUANG Feng, XIONG Ren-wei, LIN Jing-dong, ZHAO Zheng, YANG Pan-xin
    EARTHQUAKE    2024, 44 (1): 1-18.   DOI: 10.12196/j.issn.1000-3274.2024.01.001
    Abstract27)      PDF(pc) (8413KB)(25)      
    435 tributary basin standardised steepness indices (ks), 43 tributary valley width-height ratio (VF), 55 basin Area-elevation integral index (HI), 10 tributary channel longitudinal profiles and knick points were extracted by using 30 m resolution SRTM DEM data for the middle section of the Jiali Fracture Zone (Niwuxiang-Guxiang). Based on the river steepness indices of different reaches and the distribution characteristics of a series of rift points along the river longitudinal profile, the study area was divided into three areas for comparative analysis: upstream, the south side and the north side of the lower part. The upstream ks and HI were lower than the downstream values, while the VF values were higher than the downstream values. The study results indicated that the tectonic uplift activity in the downstream area of the middle section of the fault was strong, while the uplift in the upstream area was relatively weak. Five tributaries from the north and south were selected respectively for analysis in the downstream part of the Niwuxiang-Guxiang section, and the remote sensing interpretation results showed that the fracture spreads roughly along the southern side of the river valley, and was mostly in the same position as the development of low elevation rift points of the first-order tributaries on the southern side. Combining with the results of the field fracture profile survey and dating result, the analysis suggested that the middle section of the fracture was of early Holocene or late Pleistocene age, and was accompanied by significant recoil extrusion in addition to right-slip activity. The reason was that the middle section of the fault was located directly north of the eastern tectonic junction of the Qinghai-Xizang Plateau, and it was assumed that in addition to the eastward transport of the Qiangtang block, the recoil is the result of the continuous northward pushing of the tectonic junction.
    Vibration Measurement Technique of Reference Prism in Free-falling Absolute Gravimeter
    HUANG Shi, ZHU Xiao-yi, XUE Bing, ZHANG Bing, WU Xu
    EARTHQUAKE    2024, 44 (1): 50-63.   DOI: 10.12196/j.issn.1000-3274.2024.01.004
    Abstract21)      PDF(pc) (4694KB)(19)      
    Accurately measuring the vibration signal of the absolute gravimeter reference prism and using it to compensate for the absolute gravity measurement is one solution to improve the measurement accuracy of the absolute gravimeter. In this regard, this article introduces the principle of reference prism vibration measurement, designs a reference prism vibration acceleration measurement device, and derives the transfer function of the reference prism vibration measurement device. The result shows that the measurement device can be equivalent to an accelerometer. Through mature accelerometer measurement methods, equivalent accelerometer transfer function parameters can be obtained, thereby obtaining the transfer function of the output voltage of the measurement device to the vibration acceleration of the reference prism. The vibration acceleration of the reference prism can be solved to compensate for absolute gravity measurement. On the basis that the data measured in the laboratory are consistent with the theoretical data, through the vibration experiment of the vertical vibrating pendulum at the National Earth Observatory in Beijing, it is found that the experimental curve coincides with the amplitude-frequency characteristic curve described by the theoretical model formula, verifying the reliability of the reference prism vibration measurement in actual use.
    Focal Mechanism for the December 18, 2023, Jishishan MS6.2 Earthquake in Gansu Province
    WANG Qin-cai, LUO Jun, CHEN Han-lin, MENG Lin-xin
    EARTHQUAKE    2024, 44 (1): 185-188.   DOI: 10.12196/j.issn.1000-3274.2024.01.015
    Abstract21)      PDF(pc) (2197KB)(15)      
    The Cut-And-Paste (CAP) method is used to invert the focal mechanism solution of the MS6.2 earthquake that occurred on December 18, 2023, in Jishishan, Gansu Province, using regional network data. The result demonstrates that the earthquake is of the thrust type, which is consistent with the solutions provided by the USGS, GFZ, GCMT. The strike of fault plane II is in good agreement with the eastern margin fault of Jishishan.
    Design and Implementation of Borehole Comprehensive Observation Timing System
    WU Xu, XUE Bing, LI Jiang, ZHU Xiao-yi, ZHANG Bing, HUANG Shi
    EARTHQUAKE    2024, 44 (1): 37-49.   DOI: 10.12196/j.issn.1000-3274.2024.01.003
    Abstract20)      PDF(pc) (3828KB)(23)      
    It is very important to realize accurate and reliable transmission of Pulse Per Second (PPS) in borehole seismic comprehensive observation. Aiming at this requirement, a Orthogonal Frequency Division Multiplexing (OFDM) symbol is designed, and some frequency points are selected to mark the second pulse (PPS) for transmission, avoiding the transmission of second pulse (PPS) with a separate wire. It saves hardware resources and improves transmission reliability. In addition, due to the frequency band limitation of the transmission channel and the influence of the filter in the receiving process, the delay of the direct transmission second pulse (PPS) is difficult to judge, and the phase-frequency characteristics of the channel and filter are determined and measurable. When the transmission second pulse (PPS) is marked by sine wave, the delay deviation caused by the filter can be calculated based on the phase-frequency characteristics of the filter. Therefore, it is possible to correct the influence of the channel and filter. The calculation error of the time shift based on the sine wave marked transmission second pulse (PPS) can reach the microsecond level, which can fully meet the requirements of the current seismic observation.
    Correlation Analysis of Shear Wave Velocity and Burial Depth in Rock and Soil in the Yulin Area
    ZHENG Meng, HUANG Yue-min, LIANG Ji-wei, HE Si-yuan, LI Xu-dong, CHEN Hong-wei, SU Bo, SU Xiao-ming, XIE Chao
    EARTHQUAKE    2024, 44 (1): 78-93.   DOI: 10.12196/j.issn.1000-3274.2024.01.006
    Abstract20)      PDF(pc) (3755KB)(9)      
    Shear wave velocity of rock and soil is a crucial parameter in the fields of geological engineering, seismic engineering, and engineering exploration. In this study, we quantitatively investigate the relationship between shear wave velocity and burial depth for six common types of soil in Class Ⅱ sites in the Yulin area, using 218 borehole data as the research foundation. Parameters are optimized using the least squares method, and goodness of fit, root mean square error, and median error are employed as evaluation metrics. Based on these findings, we provide recommended functional models and their applicable ranges. To validate the reliability of our proposed model, we compare it with two commonly used models using borehole data from two engineering sites. The results demonstrate a significant positive correlation between shear wave velocity and burial depth for different soil types in the study area. The correlation patterns between burial depth and shear wave velocity vary for different rock types and should be analyzed on a case-by-case basis. After optimizing the model parameters and comparing three model evaluation metrics, we find that a third-degree polynomial expression is more suitable. This research contributes to a better understanding of the relationship between shear wave velocity and burial depth in rock and soil, offering valuable insights for engineering projects in the Yulin area.
    Preliminary Analysis of the Seismogenic Tectonics for the 2023 Jishishan MS6.2 Earthquake in Gansu Province
    YANG Pan-xin, XIONG Ren-wei, HU Chao-zhong, GAO Yuan
    EARTHQUAKE    2024, 44 (1): 153-159.   DOI: 10.12196/j.issn.1000-3274.2024.01.011
    Abstract19)      PDF(pc) (3024KB)(10)      
    On December 18, an MS6.2 earthquake occurred in Jishishan County, Gansu Province, which causing casualties and property losses. The earthquake occurred on the northeastern margin of the Qinghai-Tibet Plateau where developed two groups of typical fault structures due to the extension of the Qinghai-Tibet Plateau to the northeast. The NWW trending large left-lateral strike-slip faults are seemed as the boundaries of the active blocks, and the other group of NNW-trending right-lateral strike-slip faults develop within the blocks as the secondary block boundaries. The Jiashishan MS6.2 earthquake occurred in the large compression stepover between the NWW-trending left-lateral strike-slip fault zone of the north margin West Qinling and the NNW-trending Riyueshan right-lateral strike-slip fault zone, and the seismogenic tectonic is determined to be the southeastern segment of Lajishan fault zone named eastern margin of Jishishan fault. The distribution of aftershocks are strictly limited to the south of Yellow River and within the Dahejia tertiary basin in the eastern piedmont of Jishishan. The ridgelines and piedmont lines on the eastern section of Lajishan and Jishishan are discontinuous, and there are fault triangle faces along east bank of Yellow River which flows between the two mountains. It is speculated that a transverse fault with the function of adjusting the regional differential compression deformation is developed in this area. This fault cuts the southeastern segment of Lajishan fault zone and may make the eastern margin of Jishishan fault to be an independent active segment with a length of less than 40 km. It is determined that the possibility of a larger earthquake occurring in this area is not high in near future.
    Deep and Shallow Deformation Tectonics of Jishishan MS6.2 Earthquake on 18 December 2023 in China
    GAO Yuan, LI Xin-yi, LI Shu-yu, XIA Xin-yu, YANG Yi-wen, WANG Qiong
    EARTHQUAKE    2024, 44 (1): 160-166.   DOI: 10.12196/j.issn.1000-3274.2024.01.012
    Abstract18)      PDF(pc) (5209KB)(10)      
    On December 18, 2023, an MS6.2 Jishishan earthquake occurred in Gansu Province, China. The direction of absolute plate motion and lithospheric azimuthal anisotropy were consistent in the source area and around. The deformation features by the regional shallow surface deformation and the upper crustal anisotropy display distinct spatial perturbations. The local inhomogeneous deformation of the upper crust and the difference in physical properties are the deep seismogenic tectonic setting of the Jishishan earthquake. The earthquake occurred at the Jishishan east margin fault, which is approximately 30~40 km long. There are no deep seismogenic tectonic conditions along this fault that could trigger earthquakes of comparable or larger magnitudes in the near future.
    Source Rupture Process of the 2023 M6.2 Jishishan, Gansu Earthquake Using the Regional Seismic Data
    LUO Yan, ZHU Yin-jie, GAO Yuan
    EARTHQUAKE    2024, 44 (1): 189-194.   DOI: 10.12196/j.issn.1000-3274.2024.01.016
    Abstract18)      PDF(pc) (2612KB)(10)      
    We carried out the inversion for finite-fault rupture process of the 2023 M6.2 Jishishan earthquake using the regional broadband seismic data. The result shows that the seismic fault of the Jishishan earthquake is thrust with slight strike-slip components. The rupture lasted about 9 s and the most seismic energy is mainly released within 6 s. The finite-fault slip model shows that the Jishishan earthquake rupture initiated from the hypocenter and expanded northwestward along the fault strike. The total seismic moment released by this fault is 1.39×1018 N·m equal to MW6.02. The rupture length is about 10 km with a maximum coseismic slip of 35 cm.