Serpentine minerals are among the minerals commonly found in the Earth’s subduction zones, and their unique physicochemical properties have a significant impact on subducting geodynamics. Friction experimental studies of serpentine minerals are essential to gain a deep understanding of the frictional sliding stability of serpentine-containing faults in subduction zones as well as explaining the complicated misalignment behavior of faults in subduction zone. Previous laboratory research has produced an abundance of results, and this work addresses two main aspects: the stable states of occurrence and interconversion relationships of serpentine minerals, and the parameters affecting the frictional strength and sliding stability of serpentine minerals. First of all, studies on the stable endowment state of serpentine minerals and the interconversion relationship show that different types of serpentines diaplay different stable phases under different conditions. Chrysotile and lizardite are stable at low temperatures, and the stability fields of both chrysotile and lizardite roughly overlap, but chrysotile is in a substable state. Antigorite is stable at high temperature conditions, such as subduction zone mantle wedges containing high pore fluid pressure conditions, and undergoes a transition from lizardite to antigorite with increasing temperature. Secondly, studies on the factors controlling the frictional strength and sliding stability of serpentine minerals have shown that temperature, pore fluid, and the effective normal stress are all critical factors, for example, an increase in temperature can significantly increase the frictional strength of lizardite and chrysotile. In addition, the friction strength of serpentine minerals shows an obvious pressure dependence, and it was found through previous experimental studies that the friction strength of chrysotile exhibits a high-pressure sensitivity, and that the friction strength of antigorite gradually increases with increasing temperature under low fluid pressure conditions, showing an obvious temperature strengthening phenomenon. In contrast, the change in frictional strength of antigorite with temperature under high-pressure fluid pressure conditions is diametrically opposed to the results of low-pore fluid pressure conditions, which shows a clear temperature weakening phenomenon. Previous studies have also found that antigorite-undergoes a dehydration reaction with increasing temperature under lower fluid pressure conditions, and then exhibits unstable velocity weakening phenomenon, while antigorite exhibits velocity weakening phenomenon under low shear deformation rate under high-pressure fluid conditions. By analyzing the variation of friction-slip stability of antigorite with the shear slip rate can help us to better explain the phenomenon of subduction-zone slow-slip. Overall, experimental studies of the friction of serpentine minerals provide a key experimental basis for a deep understanding of subduction zone geologic processes. The results of these studies are scientifically important for predicting earthquakes and explaining the evolution of the Earth’s internal tectonics and subduction zones, providing strong support for research and practice in the field of geosciences.

The migrating and enriching of fault gas during dynamic load-unload process are important indexes to evaluate the stress state and tectonic activity of underground medium. The Hutubi underground gas storage provides a natural experiment site for the analysis of the relationship between the gas geochemistry and the stress-strain status. In this paper, the soil gas concentrations of Rn, CO₂, Hg and H₂ during the gas injection in the Hutubi underground gas storage were analyzed. The results show that the soil gas contents and changing trend are close to the background value in the non-reservoir area and fault zone, which may reveal the weak activity of the fault. Significantly higher concentrations of soil gas H₂ and Hg are observed in the gas storage area, where H₂ maximum reaches 5.551×10^-4 and Hg maximum reaches 53ng/m³. Moreover, the abnormal soil gas H₂ and Hg measurement locations are more consistent. The variation trends of soil gas Hg, H₂, Rn, and CO₂may be related to the different gas generation and response mechanisms. The concentrations of soil gas H₂ and Hg are sensitive to the variation of pressure and the development of cracks in the underground gas storage, and they can reveal gas injection's effect on fault activity. This study provides a new basis for analyzing the influence of gas injection and withdrawal in Hutubi underground gas storage on fault activity.

Beijing plain area has been always characterized by the tectonic subsidence movement since the Pliocene. Influenced and affected by the extensional tectonic environment, tensional normal faulting occurred on the buried NE-trending faults in this area, forming the "two uplifts and one sag" tectonic pattern. Since Quaternary, the Neocathaysian stress field caused the NW-directed tensional shear faulting, and two groups of active faults are developed. The NE-trending active faults include three major faults, namely, from west to east, the Huangzhuang-Gaoliying Fault, Shunyi Fault and Xiadian Fault. The NW-trending active faults include the Nankou-Sunke Fault, which strikes in the direction of NW320°~330°, with a total length of about 50km in the Beijing area. The northwestern segment of the fault dips SW, forming a NW-directed collapse zone, which controls the NW-directed Machikou Quaternary depression. The thickness of the Quaternary is more than 600 meters; the southeastern segment of the fault dips NE, with a small vertical throw between the two walls of the fault. Huangzhuang-Gaoliying Fault is a discontinuous buried active fault, a boundary line between the Beijing sag and Xishan tectonic uplift. In the Beijing area, it has a total length of 110km, striking NE, dipping SE, with a dip angle of about 50~80 degrees. It is a normal fault, with the maximum fault throw of more than 1 000m since the Tertiary. The fault was formed in the last phase of Yanshan movement and controls the Cretaceous, Paleogene, Neogene and Quaternary sediments.There are four holes drilled at the junction between Nankou-Sunhe Fault and Huangzhuang-Gaoliying Fault in Beijing area. The geographic coordinates of ZK17 is 40°5'51"N, 116°25'40"E, the hole depth is 416.6 meters. The geographic coordinates of ZK18 is 40°5'16"N, 116°25'32"E, the hole depth is 247.6 meters. The geographic coordinates of ZK19 is 40°5'32"N, 116°26'51"E, the hole depth is 500.9 meters. The geographic coordinates of ZK20 is 40°4'27"N, 116°26'30"E, the hole depth is 308.2 meters. The total number of paleomagnetism samples is 687, and 460 of them are selected for thermal demagnetization. Based on the magnetostratigraphic study and analysis on the characteristics of sedimentary rock assemblage and shallow dating data, Quaternary stratigraphic framework of drilling profiles is established. As the sedimentation rate of strata has a good response to the activity of the basin-controlling fault, we discussed the activity of target fault during the Quaternary by studying variations of deposition rate. The results show that the fault block in the junction between the Nankou-Sunhe Fault and the Huangzhuang-Gaoliying Fault is characteristic of obvious differential subsidence. The average deposition rate difference of fault-controlled stratum reflects the control of the neotectonic movement on the sediment distribution of different tectonic units. The activity of Nankou-Sunhe Fault shows the strong-weak alternating pattern from the early Pleistocene to Holocene. In the early Pleistocene the activity intensity of Huangzhuang-Gaoliying Fault is stronger than Nankou-Sunhe Fault. After the early Pleistocene the activity intensity of Nankou-Sunhe Fault is stronger than Huangzhuang-Gaoliying Fault. The activity of the two faults tends to consistent till the Holocene.

Identifying the source of the observed fluid anomalies is a major tast in verifying the anomalies in seismic subsurface fluid research. The stable hydrogen and oxygen isotopes are proved to be effective to trace the underground fluid origin and its development. In this study, we summarized the basic principles, water sampling and testing techniques in recognizing the fluid anomalies by using the stable hydrogen and oxygen isotopes. We also enumerated the related applications in analyzing the sudden water level increase and the rapid shifting from limpid water to murky. The stable hydrogen and oxygen isotopes analysis can be used to verify the macroscopic underground fluid anomalies, such as subsurface water temperature, water level and chemical component changes, and the wide use of this method in seismic subsurface fluid research will be helpful to identify the tectonic or non-tectonic related influencing factors to the fluid anomalies.

Hydrogen is recognized as one of the most useful gases to detect fault activities. Based on long-term high-accuracy soil hydrogen observation data in fault zones, the paper evaluates the reliability of data according to the distribution of measurements. Through the evaluation of earthquake-reflecting ability of hydrogen concentration, we consider that there is a certain corresponding relationship between hydrogen concentration and seismic activity and we present the judging index for this anomaly. Hydrogen concentration characteristics with the earthquakes within the range of 350km around the station were analyzed, especially the two earthquakes, which occurred on October 24, 2010 and March 8, 2011 in Taikang, Henan Province, with magnitude M_S4.6 and M_S4.1 respectively. The observation station is located at Xiaxian in Shanxi Province, 300km away from the epicenter. In a week before the two earthquakes, high-accuracy soil hydrogen concentration measurements showed similar anomaly variation, which was increasing abruptly, then decreasing, and after the earthquakes it returned to background level. Overall, the changing scope was more than 20 times of the background value. We concluded that the anomaly was affected by tectonic setting of the earthquakes. The similar hydrogen distribution pattern recorded at the same station is attributed to the same tectonic position and focal mechanism solution. The hydrogen could be an effective tool for short-term and imminent earthquake prediction, which provides reference for short-term and imminent earthquake prediction in areas with high earthquake risk.

We summarized the fluid anomalies associated with the Ludian M_S6.5 earthquake based on the Sichuan and Yunnan earthquake network observations and field survey. The fluid anomalies were divided into long-term, medium-term, short-term, imminent and macroscopic anomalies according to the basic principles of earthquake forecasting. The long-term and medium-term anomalies distributed mainly in the range 300～500km away from the epicenter. By contrast, the short term, imminent and macroscopic anomalies clustered in an epicentral distance less than 100km. The underground fluid anomalies in the higher station density area reflect the enhancement of fluid movement, which are conducive to determine the seismic risk area and trace the short-term precursor of earthquake. The regional stress variations may cause the fractures in a fault zone open and close, leading to the change of water level and temperature in boreholes or spring and emission of deep-sourced gases. It may also lead to intense water-rock reaction and groundwater intrusion, resulting in the change of ion contents in groundwater, or sometimes, the occurrence of significant macroscopic anomalies. Therefore, it is highly possible to obtain reliable earthquake precursor information for predicting the forthcoming earthquake risk zone in the region with dense observation stations.

Through a series of analysis on the black gouge at Pingxi in Yingxiu-Beichuan Fault, we found about 9wt.%organic matter of kerogen type preserved in the black gouge. The gas chromatography mass spectrometry (GC-MS) was applied to the organic matter and five major alkane compounds were identified, namely, n-alkanes (C₁₄-C₂₁), acyclic isoprenoids(pristane and phytane), sterane, terpane and n-alkylcyclohexanes (C₁₀-C₂₁). Based on preliminary analysis on the organic compounds, we conclude that the organic matter in the black gouge should have deposited in a sea facies or in a saline lacustrine reducing environment, with features of long-time storage and high maturity degree. Through contrast experiments between original gouge samples and organic-removed gouge samples, we found that organic matter in the Pingxi black gouge can significantly weaken fault frictional strength and increase its sliding stability.

Regional groundwater level change, such as rising or falling, may provide earthquake precursor information. The groundwater levels in earthquake observation wells have been rising in Jiangsu Province since 2008. By analyzing hydrochemical and physical characteristics of the Su-18 well water and surface water nearby, we studied the relationship between groundwater level anomaly and supply of surface water and atmospheric precipitation. Furthermore, we discussed the source of water supply to Su-18 well and the corresponding relationship between the rising water level and the M_S4.9 earthquake. The results show that, the groundwater of Su-18 well and reservoir water nearby are recharged by meteoric waters based on analysis of ion contents and hydrogen and oxygen isotopes. The method of assessment of precipitation recharge to groundwater by the chloride concentration found that the rise of water level is related to the increased rainfall over the same period. There are also hydraulic connections between the surrounding reservoir and Su-18 well. Impoundment activities of reservoir have impact on the groundwater recharge. In summary, the factor affecting the groundwater level anomaly at Su-18 well in 2011 is impoundment of reservoir which was affected by atmospheric precipitation. Reservoir water supplies well water through lateral permeation. This conclusion provides a basic reference for determining water level anomalies in earthquake observation wells in the future.

Xiadian Fault zone is a NNE-trending lithospheric-scale regional deep fault in the eastern part of the capital,also an active fault zone with strong earthquake activities in the history. According to the results of gravity,shallow seismic and high-density electrical geophysical prospecting,by "relay stitching" vertically from the deep to the shallow,and in combination with the methods of drilling and other means,the Xiadian Fault zone is studied by dividing it into two parts: the bedrock fault zone and the Quaternary fault zone,and new insights are gained on the characteristics of deep structure and activity of the Xiadian Fault zone. The results show that: (1)the bedrock fault zone of Xiadian Fault consists of main faults and secondary faults. Its northern part,the Mafang-Xiji area,is composed of two major faults with a narrower width,and the southern part,the Xiji-Fengheying area,is composed of three major faults,with a wider width; (2)The Quaternary fault zone of Xiadian Fault is the upward extension of the bedrock fault zone,which is the visual representation of the latest activity of the fault zone and controlled by the bedrock fault zone. The Quaternary fault zone is also composed of main faults and secondary faults. The northern part(Mafang-Xiji area)consists of two major faults and secondary faults distributed in the northern end,corresponding well with the bedrock fault zone. Occurrence of the two major faults is quite different,and the latest movement of the faults is both in Holocene. While,the southern part of the fault zone(the Xiji-Fengheying area)is quite discontinuous and is difficult to distinguish between the major and secondary faults. The faults have poor correspondence to the bedrock ones and are inferred to be related with the segmentation of faulting of the bedrock faults. Both major and secondary faults are steep and the date of their latest movement is late Pleistocene-early Holocene; (3)The amount of vertical dislocation of the bottom boundary of the Holocene sediments in the hanging and foot walls of Xiadian Fault zone is 1.7～4.8m,and that of late,middle and early Pleistocene are 6～26m,26～167m and 44～330m,respectively. The vertical dislocation on the whole fault zone differs greatly,with the highest in the Xiadian area,and decreasing gradually to the south and north ends; (4)Considering the spatial distribution,structure,occurrence,activity and characteristics of seismic activity along of the fault zone,the Xiadian Fault zone is divided into the southern and northern segments with the Zhangjiawan Fault as the boundary. The northern part experienced intensive Quaternary activity,with frequent moderate and small earthquakes. Quaternary activity is weak along the southern part,where only small earthquakes occurred.