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。

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.

In this paper, the 2022 Qingzhou M_L4.1 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 M_L4.1 earthquake, and the change is related to the underground material migration caused by the earthquake preparation and occurrence.

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.

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 M_L≥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.

This article utilizes the Total Electron Content (TEC) data measured by the GPS stations of the Chinese Mainland Crustal Movement Observation Network (referred to as the “Crustal Network” hereafter) to establish an empirical ionospheric model for the Beijing-Tianjin-Hebei region. By incorporating solar flux and geomagnetic activity data, the performance of the model is enhanced. The study develops a functional model for the diurnal, seasonal variation, and geomagnetic effect components of the ionospheric TEC, using a nonlinear least squares method to fit the coefficients. A multi-parameter empirical fusion model is proposed-the Ionospheric TEC Beijing-Tianjin-Hebei Region Model (MEFM-ITBTHR) - to predict the ionospheric TEC in the Beijing-Tianjin-Hebei region. Results indicate that the MEFM-ITBTHR model fits the modeling dataset well. The performance of the MEFM-ITBTHR model is further analyzed through geographical variation, seasonal variation, and geomagnetic disturbance analysis. Results demonstrate that in the Beijing-Tianjin-Hebei region, the MEFM-ITBTHR model exhibits better forecasting accuracy, linear correlation, and model precision for measured TEC across different latitudes, seasons, and geomagnetic disturbances compared to the IRI2020 and NeQuick2 models. The regional TEC empirical model constructed in this study provides a new method for ionospheric delay correction for GNSS single-frequency users and holds significant reference value for establishing other new and improving existing empirical ionospheric models.

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.

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.

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.

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.

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.

In this paper, we studied seismicity and relocated earthquakes with M_L≥0.5 occurring in the Jinping reservoir and its surrounding area before and after the impoundment. Then we inversed the mechanism solutions of 71 M_L≥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.

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.

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 M_S6.9 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.

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 M_S6.0 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 M_S≥6 in the next five years.

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 M_S6.0 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 M_S6.0 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.

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.

On December 18, an M_S6.2 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 M_S6.2 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.

On January 1, 2024, a large earthquake with magnitude 7.6 struck the Noto Peninsula in Japan, causing significant casualties and property damage. This paper provides a quick analysis of the focal characteristics, damage and emergency response, using information in three days after the earthquake. The results show that: ① The rupture of the earthquake was thrust type, and the distribution of aftershocks showed a NE zonal character with ~150 km range. ② GNSS observed a significant west-northwest coseismic displacements in the epicenter annex, with maximum horizontal displacements of 1.2 m, and the two-segment fault inversion model was able to fit the observed data well. ③ The large PGV and PGA, with maximums of 145 cm/s and 2,681 cm/s², were observed in the vicinity of the epicenter. This earthquake produced the highest value (7 degree) of the Japanese Intensity Scale near the epicenter, and all the areas in the Noto Peninsula were above 5+ (the Japanese Intensity Scale). ④ The recent earthquake has so far resulted in 73 fatalities and 323 injuries in Ishikawa Prefecture. Additionally, 183 buildings have been either completely or partially destroyed. The seismic event also triggered a series of cascading disasters, including tsunamis, fires, slope failures, and road damages. Finally, we briefly summarize the emergency measures in disaster response, including emergency relief and information dissemination. This work provides a reference case for understanding the mechanisms of earthquakes, studying the mechnism of disasters, and developing effective responses, further, provides lessons for handling similar events in the future.

At 23:59 Beijing Time on December 18, 2023, an M_S6.2 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 M_S6.2 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.

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.

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.

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 M_S4.2 earthquake in Qinghai on December 24, 2020, and the Yushu M_S4.7 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 M_S4.2 earthquake spectrum is wide, the dominant frequency band is 0~5.0 Hz. The frequency band of the Yushu M_S4.7 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.

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.

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 M_W5.0 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 M_W7.3 earthquake. If the two segments rupture simultaneously, the released seismic moment energy is equivalent to an M_W7.5 earthquake. The seismic risk of the Maqin-Maqu segment is worth poajing attention to.

On December 18, 2023, an M_S6.2 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.

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.

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.

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.

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 3^rd, 2014 Ludian M_S6.5 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 LudianM_S6.5 earthquake are consistent with the characteristics of the database of coseismic landslides in mountains and valleys triggered by other strong earthquakes in western China.

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.

In order to study the stress implication of the 2023 M_S6.2 earthquake in Jishishan, Gansu on the surrounding areas, the central focal mechanism solution of the earthquake is estimated based on the focal mechanism data provided by various institutes and scholars, with nodal plane Ⅰ: strike 159.08°, dip 40.57°, and rake 112.46°, and nodal plane Ⅱ: strike 310.52°, dip 53.05°, and rake 71.88°. It can be judged as a reverse focal mechanism type of this earthquake. Projecting the local tectonic stress tensor on the two nodal planes of the central focal mechanism, the resulted relative shear stress on the nodal plane are 0.797 and 0.951, respectively, which mean that the earthquake is a normal energy release under the action of the local tectonic stress field. The NNW striking of the Lajishan Northern Margin fault is dipping SWW and dip angle of 45°~55° by geological field investigation, and nearly consistent with the nodal plane Ⅰ of the central focal mechanism, we consider that the Lajishan Northern Margin fault is the seismogenic fault of the earthquake. Based on the rupture model and homogeneous elastic half-space model, we calculate the co-seismic displacement field and strain field generated by the earthquake in the surrounding areas. The volumetric strain at the epicenter area shows tensile tension, and the northeast and southwest sides far from the epicenter show slight tensile tension, and the periphery of the epicenter shows compression with strong compression on the east side. The horizontal displacement presents the outflow of material from the northwest and a small portion of the southeast side of the epicenter, while the material from the northeast and southwest sides of the epicenter is inflowed into the epicenter. Corresponding to the horizontal displacement field, the vertical displacement field is uplifted at the epicenter, while the surrounding area shows little subsidence.

435 tributary basin standardised steepness indices (k_s), 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 k_s 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.

This study used the double-difference earthquake location method combined with waveform cross-correlation technique to relocate the M_S6.2 Jishishan earthquake sequence (As of 24:00 on December 22, 2023) in Gansu Province. The results show that the epicenter of the M_S6.2 Jishishan earthquake is located at Jishishan County, Linxia Prefecture (35.745°N, 102.827°E) and the focal depth is about 12.5 km. The aftershock sequence formed two branches in different directions, which were NW and NNW. The aftershocks near the M_S6.2 Jishishan earthquake are distributed in an NW direction, and tilted toward the NE. The relocation results reveal the complex tectonic environment of the region.

The Cut-And-Paste (CAP) method is used to invert the focal mechanism solution of the M_S6.2 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.

On December 18, 2023, an M_S6.2 earthquake occurred in Jishishan County, Gansu Province. The earthquake triggered a mudflow disaster in Jintian Village, Zhongchuan Township, Guanting Basin, causing serious damage and casualties. Comparative analysis of pre- and post-earthquake high-resolution satellite/aerial images shows that the Jishishan M_S6.2 earthquake did not trigger large-scale coseismic landslides and dense soil liquefaction, but dense large-size loess landslides and soil liquefaction pits developed before the earthquake maybe triggered by paleoearthquake event (s). The mudflow disaster in Jintian village was caused by the flow of clay soil with high water content in the source area under vibration conditions, which was possibly related to the human cultivation (winter irrigation from the Yellow River).

The focal mechanism solution of the Jishishan M_S6.2 Earthquake on 18 December 2023 in Gansu Province was made an inversion by the waveform fitting method in three-dimensional space using the observed waveform from the Regional Seismic Networks in China. The results show that the moment magnitude is M_W6.02, the strike/dip/slip of the first nodal plane are 305°/56°/61° and those of the second nodal plane are 169°/43°/125°. The best fine spatial position of the waveform fitting is 102.377°E, 35.968°N, with depth of 9 km. The results show that main rupture extends along NW direction. It is inferred preliminary that the nodal plane Ⅱ is Fault-Plane, and seismogenic fault is the northern margin fault of the Lajishan mountains (eastern margin fault of the Jishishan mountain). Additionally, the event is a shallow strong earthquake induced by thrust-dominated faulting mechanism with little strike-slip component.

Surface rupture is an important feature of earthquake occurrence, and a valuable tool for studying earthquake dynamics and tectonic deformation. It is generally believed that surface ruptures are only formed by earthquakes with magnitudes of M6$\frac{3}{4}$ or greater. However, in recent years, surface ruptures have also been observed in earthquakes with magnitudes of M6.0 or less. This study aims to explore the methods for identifying surface ruptures in moderate earthquakes. The identification of the seismic structures of moderate earthquakes is challenging, mainly due to the following factors: ① the relatively small scale of surface ruptures in moderate earthquakes (such as displacement, width, length, and depth), making them easily covered by thick loess and hidden; ② non-tectonic fractures interfere with the identification of tectonic fractures. In this study, we conducted a preliminary analysis of the identification markers of the seismic structures of moderate earthquakes based on the Jishishan M_S6.2 earthquake. We proposed the following identification markers. ① geometric distribution and profile morphology of surface ruptures, linear distribution of secondary disasters (landslides, collapses, sand liquefaction, etc.) associated with earthquakes provides references and clues for identifying the seismic structure; ② the rupture runs stably across different geomorphic units along the rupture direction and at least crosses one low terrain such as a gully; ③ the rupture on the geological profile shows a stable dip; ④ tectonic morphology associated with surface ruptures that develops alternating echelons folds (compressional mounds) and tension cracks along the rupture. The identification markers proposed in this study provide new ideas for the identification of the seismic structures of moderate earthquakes.

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.