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 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.

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.

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.

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.

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.

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.

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.

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 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.

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.

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.

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.