In this study, 8071 focal parameters of small and moderate earthquakes from January 2019 to December 2023 in the Sichuan-Yunnan region were calculated. The temporal and spatial variation trends of stress drop in the focal areas of the May 21, 2021 Yangbi M_S6.4 earthquake, the September 5, 2022 Luding M_S6.8 earthquake, and key observation areas (Longmenshan fault zone and the intersection area of the Honghe fault and Xiaojiang fault) were analyzed. According to the variation trends of stress drop, significant precursor changes were observed in the 2021 Yangbi M_S6.4 focal area one year before the earthquake. The stress drop time series of the 2022 Luding M_S6.8 earthquake shows a rapid rise and decline in the short term after the main earthquake; meanwhile, the stress drop has no obvious upward trends at present. The stress drops in the intersection area of the Honghe fault and Xiaojiang fault at the southern end of the Sichuan-Yunnan rhombohedral block and the northeast section of the Longmenshan fault zone are relatively high. Consequently, the future risk of strong earthquakes deserves attention, and the stress drop changes in these two areas should be continuously observed.

Generation of the double M_S7.8 earthquakes of 6 February 2023 in southern Türkiye was comprehensively studied based on the crust structure and seismogeologic, geophysical and geothermal fluid geochemistry data as well as the spatial-temporal characteristics of the seismic sequence occurrences, in order to improve earthquake prediction and earthquake generation research. The double M7.8 earthquakes took place on 6 February 2023 in southern Türkiye, companying dozens of M≥5.0 earthquakes and several thousands of M<5.0 aftershocks in the duration of 6—17 February. Depths of the earthquakes focus range from 5 km to 22 km. The earthquake epicenters predominantly distributed in two belts in an area of about 500 km×300 km. One belt of NE trending has a length of 300 km and width of 40 km, another belt of EW trending has a length of 240 km and width of 50 km. Existences of low velocity and resistivity zone in the crust, high heat flow anomaly, negative Bouguer gravity anomaly, aeromagnetic anomaly and the deep-cut fault zones in the study area indicate that there are the necessary requirements for mantle-derived fluid accumulation and formation of super-pressure fluid bodies in the lithosphere of the area. The process of locally mantle-derived fluid accumulation to build super-pressure fluid bodies can be considered as the process of seismogenesis. The periodical accumulation of earthquake hypocenters in space and variations of the hypocenter depths during 6—17 February indicated that increasing supplement of high-energy-density fluids derived from the mantle to the earthquake source bodies, resulted in repeated increases of fluid pressure. Cryptoexplosion occurred when the fluid pressure in the source bodies exceeded the strength of the surrounding rocks (compressive strength + hydrostatic pressure), producing earthquakes. The high-energy-density fluids migrated in the way of the inflate-explosion-deflate-inflate-explosion-deflate cycle, which produced the M7.8 double earthquakes and aftershocks. Therefore, the M7.8 double earthquakes and M≥4.0 aftershocks occurring in the discontinuous inelastic source bodies in the small region can be reasonably explained from the view of energy source and seismogenesis of geothermal fluid explosion.

The M_S6.2 earthquake occurred in Jishishan County, Gansu Province, on December 18, 2023. Within a 300 km radius of the epicenter, there were 9 fixed geo-electrical resistivity observation stations. This study preprocessed the geo-electric resistivity observation data from 2 to 4 years before the earthquake, then analyzed the anomalous changes before the earthquake after eliminating annual and trend changes. It showed a declining trend in ground resistivity and a reduction in the annual variation amplitude before the earthquake at Linxia Station, Dingxi Station, and Tongwei Station, with decreasing magnitudes of 4.9% (44 km), 1.2% (164 km), and 0.6% (232 km) respectively. Earthquakes occurred during the declining reversal period. These anomaly patterns are consistent with statistical results from a large number of earthquake cases. Moreover, the closer the distance to the epicenter, the greater the magnitude of the anomaly change. This indicates that the changes in geo-electrical resistivity at these three stations are related to the M_S6.2 earthquake in Jishishan. It was also found that there was no obvious pre-seismic anomaly at the Jinyintan seismic station, which is 219 km away from the epicenter of the earthquake. Further analysis will be conducted in conjunction with the station’s actual electricity structure and fault distribution.

Hot spring water has the characteristics of deep circulation, fast-rising speed, and little human influence, and its chemical and isotopic composition carries the information of deep environment changes, it is becoming an important content of earthquake precursor monitoring. Based on domestic and foreign relevant literature, this article emphasizes the superiority of hot spring water monitoring in earthquake prediction in areas with harsh natural conditions and sparse populations, such as the Qianghai-Tibet Plateau and Xinjiang, where strong earthquakes are active. It summarizes the precursory response of the chemistry and isotope of hot spring water to earthquakes and the mechanism of abnormal response and proposes that identifying the sources of hot spring water and solute, the hydrogeochemical processes, and the seismic precursory signals during the process of earthquake breeding and occurrence are the key questions to answer how hot spring water responds to earthquakes. It is recognized that seismic prediction based on big data analysis and machine learning can play an important role in the analysis of the monitoring data of hot spring water. In addition, it is expected that the eastern margin of the Qinghai-Tibet Plateau could be the best research area to further study the mechanism of hydrochemical response to earthquakes. The purpose of this paper is to promote the development of chemical and isotopic monitoring of hot spring water for earthquake prediction and to improve the ability of earthquake prevention and disaster reduction.

Using ambient noise correlation and the moving window cross spectrum method, we detected the variations in relative seismic velocity over approximately one year before and after the eruption of the Mt. Ontake volcano in Japan on September 27, 2014, and Kilauea volcano in Hawaii, USA, on May 4, 2018, respectively, using continuous seismic data collected from the Hi-net network and IRIS. The measurement results in the 0.4~0.8 Hz frequency band for the Mt. Ontake volcanic area show that the average relative seismic velocity decreased by about 0.1% during the 10 days before the eruption and then gradually recovered after the eruption. In the Kilauea volcanic area, the measurement results in the 0.5~1.0 Hz frequency band show that the average relative seismic velocity decreased by about 0.5% during the 10 days before the large-scale eruption and then gradually recovered after the eruption ended on 4 August 2018. Combined with the results of ground tilt, GPS, and focal mechanism solutions of the two volcanic areas, it is shown that the changes in relative seismic velocity before and after the volcanic eruptions are a response to shallow magmatic inflation and deflation processes in the volcanic areas.

Ionospheric precursors are crucial indicators for short-term earthquake preparation, and abundant observations of them have been accumulated. Meanwhile, developments concerning the formation mechanisms of seismology ionospheric anomalies have led to increasing interest in the LAI coupling process, in which the AGW-agent hypothesis has been intensively discussed. Based on the BDS TEC data collected by CMONOC GNSS stations, this paper explores the spectral characteristics and spatial-temporal variations of the TEC perturbations from 14 hours before to 2 hours after the Jishishan M_W6.0 earthquake on December 18, 2023, in Gansu Province, China. According to the results, the pre-earthquake AGW-induced perturbation originated from points close to the epicenter and then dispersed outward as an arc-like structure. In addition, the background signal MSTIDs played the role of a carrier in the propagation of the perturbation, while the other two external signals exerted an interference effect on it. Finally, two promising candidates for the excitation and origination of the surface AGW signal are reviewed. Nevertheless, the connection between earthquake preparation and AGW signals needs further validation and investigation.

Medium-term earthquake prediction plays a vital role in China’s progressive forecasting system, which integrates the mid-long term earthquake prediction. It enables dynamic monitoring of long-term trend predictions and key seismic hazard zone forecasts, applies these results to annual forecasting, and provides a reliable scientific basis for short-term forecasts. The task of dynamically monitoring long-term trends and location predictions is undertaken by the Expert Group on Tracking Earthquake Situations within the General Seismic Trend. The main tasks of tracking earthquake situations within the general seismic trend include: ① Determining seismic activity trends and main active zones for the next 1—3 years or longer. This involves forecasting changes in seismic trends (e.g., increases or decreases) in Chinese mainland, predicting the highest activity levels (maximum magnitude and frequency of M7 earthquakes), and identifying major active zones of strong earthquake based on a synthesis of national seismic trends and key tectonic zone analyses. ② Assessing the urgency of earthquake occurrences in key seismic risk zones identified on a 10-year scale for the next three years. The foundation of earthquake trend and key area prediction primarily includes phase activity, anomalies in seismic activity, regional crustal deformation, and the state of regional crustal stress. While the data processing, analysis, and calculation methods employed are quantitative, the underlying approach generally relies on empirical prediction methods derived from historical earthquake cases. The identification of long-term hazardous areas relies on probabilistic predictions derived from physical models of seismic sources. Similarly, the medium-term assessment of earthquake urgency builds upon the principles of long-term prediction, incorporating dynamic tracking of fault movement, fault stress states, and seismic source anomalies. Overall, this approach combines probabilistic predictions based on seismic source models with empirical predictions derived from earthquake indicators. This study systematically presents the conceptual framework and technical system for tracking seismic trends over the next 1—3 years and assessing the urgency of long-term hazardous zones in the continental region of China. It provides a brief overview of various prediction methods, covering basic principles, technical approaches, and medium-term anomalous characteristics. Finally, based on the practice of medium-term prediction and recent research progress, the study highlights the research needs for understanding the gestation and occurrence processes of strong continental earthquakes, their precursor mechanisms, and outlines future prospects for earthquake research in China. From a business perspective, it is hoped that the development direction of medium-term forecasting can be further clarified through the phased summarization of the technical system, tracking concepts, and forecasting methods. From a scientific perspective, the development of medium-term prediction identifies basic scientific and technological needs, including the integration of field and source concepts, foundational theoretical frameworks, and key issues in earthquake dynamics. These efforts are expected to contribute to basic research in earthquake prediction and the advancement of forecasting practices.

To improve the accuracy of discriminating the seismic response of monitoring well water levels and enhance prediction efficiency, this paper conducts a comparative study using different methods on the seismic response of water level in 6 monitoring wells near two faults in the Ya’an area. First, the difference method is used to process and analyze the water level data. Then, the water level data is combined with two parameters of regional seismic activity (energy level and maximum magnitude) to analyze the relationship between regional seismic activity and water level fluctuations. Subsequently, the combined sequence was analyzed and processed in both the time domain and frequency domain. Finally, the prediction efficiency of five methods were tested using the Molchan chart method, and the optimal processing method and the monitoring well with the best prediction efficiency near the faults was identified. The results show that the combination of water level and seismic activity parameters has advantages over using the water level difference method alone, as the former can accurately eliminate the abnormal interference of seismic activity to water level. The optimal prediction methods of the six monitoring wells vary, with the optimal prediction days being within 60 days. Additionally, the study identifies the monitoring wells with the optimal prediction efficiency in the fault areas. While the combination of water level and seismic activity parameters is not universally applicable to all monitoring wells, this method can effectively reflect the extent to which water level are influenced by seismic activity.

To clarify the temporal changes in ground deformation and their causes in the Yucheng District of Ya’an City, this study used 36 scenes of Sentinel-1A satellite data from January 2019 to December 2021 and applied PS-InSAR technology to monitor ground deformation in the Yucheng District of Ya’an City. The accuracy was evaluated using concurrent GNSS observation data. By combining geological structures, precipitation, underground resource extraction, seismic activities, and other factors, the characteristics and mechanisms of deformation in the study area were analyzed. The results showed that the root mean square error (RMSE) between the PS-InSAR monitoring results and the GNSS monitoring results was 3.97 mm. The average deformation rate in the study area ranged from -28.00 to 30.12 mm/a. Under the influence of geological structures, there were significant differences in subsidence rates on both sides of the fault zones, with the maximum difference reaching 25.68 mm/a. Under the same structural control, subsidence rates had a certain relationship with human activities, mineral resource extraction, construction projects, transportation, and dense high-rise buildings all accelerated ground subsidence. Seasonal changes in groundwater levels due to rainfall had seasonal effects on ground subsidence; taking the 2019 precipitation and ground subsidence study as an example, the minimum subsidence in summer, which reached -0.14 mm.

The Sichuan-Yunnan region is located at the southeastern margin of the Qinghai-Xizang Plateau, where strong earthquakes have occurred frequently in recent years, drawing much attention to the study of strong earthquake activity trends in this area. This paper calculates the spatial distribution of M≥5.0 seismic activity rates caused by Coulomb stress perturbations resulting from 8 strong M_W≥6.5 earthquakes that occurred in the Sichuan-Yunnan region from 1976 to 2019, using the rate-state friction law and regional earthquake catalogs. The results indicate that the calculated seismic activity rates based on the rate-state friction criterion is generally consistent with the spatial distribution of M≥5.0 earthquakes that occurred between 2020 and 2023. Earthquake activity in the Sichuan-Yunnan region is jointly influenced by stress perturbations caused by strong earthquakes and seismogenic environments in different regions. The impact of strong earthquake stress perturbation fields on subsequent seismic activity is mainly concentrated in areas near strong earthquakes; while the higher seismic activity rates in some regions are related to the higher background seismic activity in the region. The areas with higher M≥5.0 seismic activity rates in the Sichuan-Yunnan region are located at the northern and southern ends of the Longmenshan fault, the Lijiang-Xiaojinhe fault, the Ruili-Longling fault, the Lancang River fault, and the Changning area. The results of this study provide new insights into the spatial and temporal distribution characteristics of moderate to strong earthquakes in the Sichuan-Yunnan region and serve as a reference for regional seismic hazard assessment.

Hot springs are closely related to tectonics and earthquakes. There is a consensus that hot spring geochemistry can be used for tectonic research and earthquake prediction. However, there is little disclosure on how to select continuous observation points for hot springs. Based on the correlation analysis between the hot springs in Fujian and the earthquakes in Taiwan, China from September 2020 to September 2023, this paper summarizes the methods for selecting hot spring observation sites and determining the sensitive components of seismic reflection. Based on this, a fluid geochemical observation network was constructed and applied to prediction practice, successfully predicting the M_L6.8 earthquake in Taiwan, China on September 18, 2022. The core of the method is to use helium, neon, and carbon isotopes from hot springs to explore hot springs with deep circulation and rich deep information. The outstanding characteristics of these hot springs are the large contribution of mantle source fluid in hot spring gas, reflected in the high ratio of mantle source helium and the mean value of the δ13C_CO2 double high region, the significant deviation of δ13C_CO2 measured value from the fitting line with CO₂ volume percentage, the intersection of structural fault zones, and the fact that most faults reach deep into the Moho plane. Water samples were collected from these hot springs for continuous observation of water chemical major ions, and the gas flow rate of Nancheng spontaneous spring with abundant escaping gas was continuously observed. The correlation analysis between the observation results and the earthquakes above M6 in the Taiwan, China was carried out by using the threshold analysis method. The seismic mapping capability of each observation point and each measurement item was calculated, and the R-value evaluation method was applied to evaluate prediction efficiency. Those with high evaluation results and high seismic mapping efficiency could be finally selected as potential effective fluid geochemical seismic monitoring points. The results can be used as a reference for selecting sites for hot spring geochemical monitoring stations and effective earthquake precursor observation projects in the earthquake industry.

The focal mechanism of the 2017 Jiuzhaigou M_S7.0 earthquake, inverted through seismic wave and InSAR observations, was mainly strike-slip, but the coseismic displacement observed by near-field GPS showed significant dip-slip characteristics in the northern section of the seismic fault. In view of this, we combines GPS and InSAR observation data to obtain rich coseismic deformation. Based on the Bayesian inversion of the geometric model of the fault, it compares and analyzes the differences in the coseismic slip distribution inverted from three data sources: GPS only, InSAR only, and fused GPS/InSAR. Thereby, it gives the optimal slip distribution model of this earthquake. The results show that the optimal model has a strike of 150° for the seismic fault, an inclination of 56°, a maximum slip of about 1.3 m, located at a depth of 5.3 km underground, and a moment magnitude of M_W6.5. Especially after adding the coseismic displacement of near-field GPS, the results show that in addition to the left-lateral strike-slip, there is also a dip-slip component in the northern section of the seismic fault. Based on the spatial distribution of the main active faults in the epicenter area, such as the Huya Fault and the Tazang Fault, this article speculates that the dip-slip property in the northern section of the seismic fault may be caused by maintaining the motion balance in the intersection area of the Tazang Fault and the Huya Fault.

This paper briefly reviews the scientific issues, analytical methods, main features, and results of years of real-time earthquake tracking practice on impending strong earthquake microfluctuations. The main characteristics of impending earthquake microfluctuations are summarized as follows: ① The dominant frequency is 11~16 Hz, and the spectrum shape is relatively neat; ② It may appear 2~24 days before the earthquake, and can be recorded by stations within a radius of 70 km of the epicenter; ③ It is reproducible and appears before multiple strong earthquakes; ④ It may be related to the magnitude of the earthquake. The greater the magnitude, the greater the possibility of impending earthquake microfluctuations before the earthquake. This paper introduces the new results of microfluctuations observed during the aftershock activity of the 2021 Yangbi M6.4 earthquake and the 2021 Maduo M7.4 earthquakes. It is inferred that the microfluctuations of imminent strong earthquakes may originate from the hypocentral area or the earthquake rupture zones.

Hydrogeochemical methods of hot springs are widely used in the research of seismic short-impending precursors. Hongmo hot spring is located in the southern section of the Anninghe fault. According to the analysis of the major elements in the water samples from Hongmo hot spring, its main hydrochemical type is Na-HCO₃. The test of hydrogen and oxygen isotopes in Hongmo hot spring shows that meteoric water is the modern recharge of groundwater, with a replenishment elevation of about 407~619 m. The analysis of trace elements indicates that there is a low degree of water-rock interaction between the hot spring water and surrounding rock during the water cycle. According to the SiO₂ temperature scale, the heat storage temperature is 63.7℃, and the cycling depth is 2.52 km. Research on the relationship between the hydrogeochemical characteristics of Hongmo hot spring and earthquakes shows that before and after the 2020 Qiaojia M5.0 earthquake, 2022 Ninglang M5.5 earthquake, 2022 Lushan M6.1 earthquake, and 2024 Ludian M4.9 earthquake, the Cl^-, Na⁺, SO^2-₄, and δD showed different degrees of anomalies. Therefore, Hongmo hot spring is an ideal site for short-impending seismic monitoring through hydrogeochemistry.

In this study, we utilized the adjoint-state traveltime tomography based on eikonal equation to invert the surrounding area of M_S7.3 Landers earthquake by time-evolving method. The inversion obtained high-resolution three-dimensional P-wave and S-wave velocity structures for different time windows. The correlation among the geological structures and velocity structures of the study area and seismic activity were analyzed. The results indicated that the velocity structure in the Landers earthquake source area and its surrounding area exhibited significant lateral heterogeneities, which was well consistent with the geological structure near surface, basins and faults showing relatively low velocity anomalies, and major mountain ranges showing relatively high velocity anomalies. The occurrence and distribution of earthquakes in the region were closely related to the lateral heterogeneity of the velocity structure, with most earthquakes occurring within high-velocity anomalies or transition zones between high- and low-velocity anomalies. There are significant differences for the velocity structure near large earthquakes in different time windows. For example, in the second time window, the velocities near the Landers and Anza earthquakes became slow down, possibly due to the changes in the geological structure nearby after the large earthquakes, which in turn caused changes in velocity.

Aiming at the problem that the traditional seismic evaluation of buildings time-consuming and the difficulty in a large-scale implementation, this paper proposes a seismic capacity evaluation model for buildings based on U-Net++. The model takes U-Net++ as the backbone network, integrates multiple information sources, such as high-resolution remote sensing images, building construction age, height, use and structural types. Taking the Yucheng District of Ya’an City, Sichuan Province, as the study area, 17 comparative experiments were designed to explore the degree of influence that different features have on the seismic resilience of buildings. This work provides robust technical support for refined assessments of earthquake disaster risks on a broad scale.

The hydrogeochemical characteristics are studied by sampling geothermal hot springs/geothermal wells in eastern Shandong of the Zhangbo fault zone,measuring the main elements and hydrogen and oxygen isotopes of water samples. The results show that: ① The main chemical types of hot spring water are Ca-HCO₃, Na-Cl, Na-HCO₃, Na-SO₄. ② The measured values of δD and δ¹⁸O are -39.90%~-68. 00% and -5.00%~-8.50%,which fell near the meteoric water line in China and the meteoric water line in eastern China, indicating that the hot springs was meteoric water. According to the calculation, the minimum circulation depth in the study area of hot springs is 1183 m, the maximum circulation depth is 4271 m, and the general variation range of recharge elevation is 430.0~1366.6 m. ③ The variation range of γ_Na/γ_Cl in Shandong region is 0.509~38.37,among which, the metamorphism coefficient of Linqulan Cuihu and Cishan hot spring are relatively high, that indicate that it is affected by mineral leaching. ④ The Na-K-Mg triangle diagram shows that most of the hot springs water samples are partially mature water, only the Yuquan hot spring in Gaoqing County being equilibrium water.

The seismic observation wells in Baodi area, Tianjin, have been the precursor sensitive wells in the Beijing-Tianjin-Hebei region, but their hydrogeochemical characteristics is less studied. In this paper, three seismic observation wells on the north and south sides of the Baodi Fracture were selected to analyze the ionic component concentrations, hydrogen and oxygen isotope compositions, silica and carbon isotope contents, and to carry out hydrogeochemical characteristics, and the results show that: ① The hydrochemical types of Baodi Xin well and the surrounding cold-water wells in the northern part of the Baodi Fracture were dominated by Na-SO₄-HCO₃ types, and the hydrochemical types of Wang 3 well, Wang 4 well and the surrounding geothermal wells in the southern part of the Baodi Fracture were dominated by Na-HCO₃ types. Wang 3 and Wang 4 wells in the southern part of Baodi Fracture and the surrounding geothermal wells are dominated by Na-HCO₃ type of water chemistry. The source of groundwater is atmospheric precipitation, and the recharge area is the northern Yanshan Mountains. The cold water and geothermal water on both sides of the Baodi Fracture are located in the immature water zone, indicating that both of them are mixed by shallow cold water in the upward transportation process. The depth of geothermal water circulation on the south side of the fracture is significantly higher than that of the cold water on the north side, and the Cl^- of geothermal water has a deep origin. The inorganic carbon isotopes of the cold water and the geothermal water show zoning characteristics. The carbonate minerals in the cold water on the north side of the fracture are not saturated, and the carbon source of the geothermal water on the south side of the fracture is the leaching of carbonate minerals from the recharge zone and the dissolution of the carbonate aquifer. ④ Although the recharge zones of cold water and geothermal water on both sides of the Baodi Fracture are the same in the northern Yanshan Mountains, different types of groundwater on both sides of the fracture are formed due to the differences in hydrogeological conditions, circulation paths, and circulation depths at the locations of the observation wells, as well as the controlling effect of the Baodi Fracture on the hydrological and geochemical evolution of the groundwater on both sides of the fracture. The results of this paper enrich the geochemical background field data in the Beijing-Tianjin-Hebei region, and provide a scientific basis for exploring the geochemical characteristics of regional subsurface fluids.

Taking the observation spring (Xiangcheng Ranwu hot spring ) in Xiangcheng, Sichuan as the research object, we collect water samples from observation spring and other nearby hot springs and analyze the main chemical ions compositions, trace elements and hydrogen and oxygen isotope compositions to study water cycle characteristics and formation mechanism of the hot spring. The results show that, the hot spring hydrochemical type is Na-HCO₃, and belongs to medium temperature, alkaline, low salinity hot spring and contains B, Li, Ba and other trace elements. Ions in hot springs are mainly dissolved from silicate minerals in surrounding rock during water-rock interaction. The stable hydrogen and oxygen isotopes (δ18O and δD) composition indicates that the main source of the recharge for the hot spring is precipitation. According to the result of Si-enthalpy model, the geothermal reservoir temperature of the hot spring is 275℃ and circulation depth of hot spring is 5.3 km. The ratio of mixing cold water with hot water is about 84%~86% which calculated by Si-enthalpy equation method. The genetic model of Xiangcheng Ranwu hot spring is that groundwater receives recharge from infiltration of precipitation in the mountain area, undergoes deep circulation and obtains heat from heat flow and flows up to the surface along the Xiangcheng fault, at the same time mixed with shallow cold water. Finally, exposing in the river valley as a medium hot spring. We relocated earthquakes in the study area by the “multi-stage” method. The results suggest that the focal depth that located near the hot spring is deeper than geothermal water circulation depth, which indicate that the geothermal cycle can weaken the fault strength and control the seismic activity around the Xiangcheng hot spring. Based on above results, we can conclude that Xiangcheng Ranwu hot spring plays an important role in earthquakes formation in this area and is suitable for further geochemical observation of earthquake precursor.

The source parameters characterize the main physical processes of an earthquake, while the velocity model is an approximate parameter representation of the real underground structure. Both are coupled in various ways, affecting the recording of seismic phases. In the past, when fitting the waveforms of a large number of regional earthquakes to invert for source parameters, low-computational-consumption one-dimensional velocity models were often used to model the seismic waveforms, and there was a lack of systematic and quantitative assessment of the absolute error in the source mechanism solution caused by the velocity model. This study takes the Longmenshan fault zone as an example, using a high-resolution three-dimensional velocity model obtained by wave imaging to accurately perform three-component broadband waveform synthesis for 212 representative regional earthquakes (M_S 3.5~5.7) after the Wenchuan earthquake, and based on this, multiple representative regional one-dimensional velocity models are used for source parameter CAP waveform inversion tests. By statistically analyzing the source parameters obtained from the waveform inversion of different one-dimensional models and comparing them with the representative seismic source parameters, the study systematically evaluates the impact of the accuracy of one-dimensional velocity models on the precision of the source parameter waveform inversion results. In this paper, under the filtered parameters for P-waves (0.01~0.18 Hz) and S-waves (0.03~0.10 Hz), the four sets of one-dimensional velocity model inversion mechanism solutions obtained are all quite reliable, with the number of events with an error Kagan angle less than 30° accounting for more than 97%. However, the CAP inversion depth error depends on the velocity model, and it is found that the inaccurate shallow structure will severely affect the inversion depth of the event. In the case of unknown accuracy of the velocity model, the normalized cross-correlation coefficient NCC of the seismic event can be used as a key indicator for the accurate inversion of the source depth. The velocity model accuracy assessment method and ideas proposed in this paper can be extended to the source inversion research of other complex tectonic areas and different one-dimensional velocity models.

Using regional hydrogeological data, water temperature gradient test results, regional groundwater exploitation data, and precipitation data, the factors affecting the multi-year and interannual changes in water level and temperature in the Tongliao earthquake observation well in Inner Mongolia were analyzed. On this basis, a hydrodynamic geological model was constructed to explore the mechanism of quasi synchronous changes in water level and temperature in the well. The results indicate that regional groundwater extraction and rainfall are the main influencing factors for the quasi synchronous changes of water level and temperature in the well, and the cold water infiltration theory can well explain these quasi synchronous changes.

Identifying the scale and spatial distribution characteristics of volcanic gas releases is of great significance for volcano monitoring and eruption prediction, assessing greenhouse gas releases from geological sources, and understanding climate changes. This paper investigates the scale and spatial characterization of greenhouse gas release in the volcanic area of Changbaishan Tianchi using the accumulation chamber method and hyperspectral gas method. The results of the study showed that: ① CO₂ fluxes in the volcanic area of Changbaishan Tianchi were in the range of 0.16~1051.39 g·m^-2·d^-1; CH₄ flux values were -0.05~4.68 g·m^-2·d^-1. The gas release from Changbaishan Tianchi volcano was spatially characterized by a ring-band distribution, with weaker gas release at the periphery of the caldera, and the strongest gas release occurring in the Julong Hot Spring Group, Jinjiang Hot Spring Group, and the cone within the range of 1800~2200 m above sea level. ② The surface and hyperspectral satellite observations of carbonaceous gases release from Changbaishan Tianchi Volcano are correlated on both temporal and spatial scales. ③ Spatial differences in carbonaceous gas emissions from Changbaishan Tianchi volcano may be controlled by the special conditions of the caldera, fault tectonics, hot spring geothermal reservoirs, and magmatism.

The underground fluid of Panjin No.1 well has been observed since 1973, which has not only enriched the means of observation, but also accumulated a large amount of observation data. The Panjin No.1 well has showed obvious abnormal changes before the several earthquakes, that provides an important reference for earthquake monitoring and prediction. In this paper, we studied the characteristics, prediction methods and mechanism of underground fluid anomalies in Panjin No.1 well. The analysis results that the anomaly characteristics and prediction methods of the underground fluid in Panjin No.1 well before earthquake indicate that, radon is mainly characterized by trend and impending anomalies, hydrogen is mainly characterized by short-term and imminent anomalies, which can use the threshold analysis, differential analysis and the critical slowing down methods to obtain a good results in identifying anomalies. Chloride ion is mainly characterized by short-term and imminent, which can use the original curve analysis method to have a good effect in extracting anomalies. The research results of the abnormal mechanism of underground fluid in Panjin No.1 well indicate that, there is a close relationship among the abnormal concentration of each measurement item, the strength of seismic activity and changes in regional stress field. Under the condition of regional compressive strain, the radon precursory anomalies in the Panjin No.1 well observation is characterized by increasing concentrations. Under a tensile strain state, the anomalies is characterized by V-shaped changes in radon concentrations.

Using high precision data processing software GAMIT/GLOBK, we obtain co-seismic displacement of the 14 earthquakes above M_W6.0 from 2011 to 2015, based on the CMONOC GPS continuous stations. Combining the tectonic background and the focal mechanism, we research the spatial distribution characteristic of co-seismic displacement field. The results show that the larger magnitude, the shallower source, the closer epicentral distance, the more obvious the co-seismic displacement can be observed by GPS stations. For the shallow source earthquakes, the observable range of co-seismic deformation effects is within 50 km for the M_W6.0~6.5 earthquakes, within 100 km for the M_W6.5~7.0 earthquakes, and exceeds 200 km for the earthquakes with magnitudes above M_W7.0.

The two M7.8 earthquakes in Türkiye on February 6, 2023, caused coseismic responses in Xin 04 well, Xin 10 well, and Xin 11 well in Urumqi, Xinjiang, but their coseismic variation patterns were different. In this paper, we compare and analyze the coseismic response characteristics of water levels in the three observation wells, and discuss the earthquake-induced changes in well water levels and their coseismic response mechanisms. The results illustrate three types of coseismic responses: oscillation at Xin 10 well, coseismic decrease at Xin 04 well, and coseismic increase at Xin 11 well, which indicates the complexity of the mechanisms of coseismic changes in well water levels. Two M7 earthquakes caused the same type of coseismic response at the same well, and the coseismic changes of water levels of different observation wells are related to changes in the permeability structure where the well boreholes are located.

In order to study the stress state at the source region of the M5.1 earthquake occurred on July 12, 2020, a dense array was deployed in this area after the earthquake. 96 focal mechanism solutions and a fine crustal stress field of 0.25°×0.25° were obtained by using 20505 P-wave first motion polarity data in the earthquake source region and its adjacent area. The results show that: The focal mechanism of small earthquakes in the Guye earthquake region of Tangshan is mainly strike-slip type, followed by normal-fault type. The P-axis is NNE oriented with large of the plunge angle, while the T-axis NNW oriented with smaller plunge angle. Moreover, we found that there is a certain angle of deflection in the P-axis azimuth in the area near the Luanxian-Laoting fault, that is, from the NEE—SWW oriented deflection on the west side of the fault to the NW—SE oriented deflection on the east side of the fault, indicating the division of the stress field by the reverse-normal activity of the Luanxian-Laoting fault. The solution and analysis of the focal mechanism and stress field of small earthquakes can provide reference for further research in this area, especially in the area near the Luanxian-Laoting fault.

In this paper, the water level coseismic response characteristics of Sichuan fluid network to the three large earthquakes, the 2022 Lushan M_S6.1, the 2022 Maerkang M_S6.0 and the 2022 Luding M_S6.8 earthquakes, are analyzed statistically. The results show that the three strong earthquakes induced different degrees of water level coseismic response in most areas of Sichuan. The coseismic responses amplitude of water level induced by the three earthquakes are significantly correlated with the earthquake magnitude, while not significantly correlated with well-epicenter distances. In a large range, the coseismic response amplitude of water level are influenced by the aquifer lithology, geological structure, and wellbore conditions. The coseismic response types of water level are mainly affected by the well-epicenter distances, and little related to the wellbore-depth. For the 2022 Luding M_S6.8 earthquake, the reason for the large difference in the coseismic response amplitude of water level of wells Chuan-20, Chuan-49 and Chuan-50 may be the different wellbore bearing capacity. Due to the effects from the aquifer lithology, the location in the fault zone and the wellbore bearing capacity, the coseismic response amplitude of the water level of wells Chuan-46, Chuan-47 and Chuan-48, being close to each other in the same fault zone, are different in the three strong earthquakes. In the 2022 Lushan M_S6.1 earthquake, the coseismic response types of water level between wells Chuan-46 and Chuan-47 are different, which may be related to the different main control factors of dynamic or static stress on the wells water level. The statistical and analytical results of water level coseismic response are affected by the sampling rate of instruments. The analysis results of water level coseismic response, using minute water level data, may not be accurate enough. The seconds water level data can provide more accurate and rich water seismic waves information for the detailed study of the water level coseismic response characteristics and mechanisms.

Both dissolved H₂ in the Urumqi 04 spring water and the H₂ in the soil of the Aksu fault belong to the A-type monitoring points of Xinjiang earthquake monitoring, prediction, and evaluation. This paper takes the two as research objects, and analyzes the dynamic variation characteristics of H₂ concentration in different occurrence forms. The R-value scoring method and Molchan chart method were used to test the earthquake-reflecting efficiency of H₂ concentration and to extract abnormal indexes. The mechanism of H₂ reflecting earthquakes in different occurrence forms is discussed and analyzed. The conclusions are as follows: The concentration of dissolved H₂ in the Urumqi 04 spring water is less affected by meteorological factors, while the concentration of H₂ in the soil of the Aksu fault is influenced by both air pressure and air temperature, mainly by air temperature. The R-value scoring method and Molchan chart method showed that both monitoring points had good short-term prediction efficiency. The good short-term prediction performance of H₂ measurement is due to the stable physical and chemical properties of H₂ and its extremely fast migration speed.

The AlphaGUARD radon meter is generally widely used as a radon standard instrument for value transfer. This article studied the accuracy of the AlphaGUARD radon meter in low range and consistency in high range, and established a linear relationship for value transfer within the range of 0.6~142.4 Bq·L^-1. Based on tracing to reference standards, radon standard instruments are used to transfer values to circulating radon sources. Quantity transfer experiments based on circulating radon sources, as well as quantity transfer experiments based on standard instruments and certain concentration water samples (greater than 5 Bq·L^-1), are conducted separately. Seven technical schemes for transmitting measurement values using radon standard instruments have been developed for four new types of radon meters used in the underground fluid network in recent years, and have been applied in more than 40 radon observation stations nationwide. The continuous application of 12 observation stations for 2 years has shown that the radon value transmission technology scheme is scientifically feasible. Among the 12 radon observation stations, the relative deviation coefficients was less than 5%. This technology scheme can meet the calibration needs of existing radon observations. In addition, uncertainty evaluation experiments were conducted on the transmission scheme. Taking the DDL radon meter as an example, its minimum uncertainty can reach 5.5% (coverage factor k=2). The radon measurement value trans mission technology established in this study is scientifically feasible, and the application plan can effectively ensure the stability and reliability of the new radon measurement instrument.

The northern section of the Longxian-Baoji fault zone has a strong degree of locking, but the locking degree of its southern section is less studied. The observation well of a confined aquifer is considered a sensitive “volumetric strain gauge”, and the rise or fall of the well water level often reflects the state of regional stress in tension or compression. Fengxiang Well in Shaanxi is located in the central and southern section of the Longxian-Baoji Fault. Based on the analysis of the variation trend of the water level in Fengxiang Well from 2013 to 2023, the porosity of the aquifer, the volume compression coefficient of the solid skeleton, and the volume compression coefficient of the water were calculated for the aquifer of the well, under un-drained conditions, by using sliding fits such as the barometric pressure coefficient and the M₂-wave tidal factor. The temporal characteristics of the tectonic stress field around the well were quantitatively analyzed by using the relationship between the water level variation of the well and the vertical stress variation of the aquifer. Based on the GNSS baseline and surface strain variation characteristics within the region, as well as the seismic activity characteristics since 2013, a comprehensive analysis suggests that the stress field variation characteristics in the region can be divided into two stages: ① From 2013 to 2017, the water level of Fengxiang well decreased, and the vertical stress weakened, showing a tensile environment with low seismic frequency. ② From 2017 to 2023, the water level of Fengxiang well tended to stabilize, and the vertical stress fluctuated around zero. The tension weakened and gradually transformed into a stage of stress accumulation and enhancement, with a significant increase in the number of earthquakes. Based on the analysis of the water level, vertical stress, GNSS baseline and surface strain, as well as seismic activity characteristics in the Fengxiang well over the past decade, it can be concluded that the central and southern sections of the Longxian Baoji fault zone is in a relatively stable state with weak stress accumlation and small deformation.