Using seasonal gravity observation data from Urumqi and its surrounding areas, collected between April 2019 and April 2022, this paper applies absolute gravity control to perform classical adjustment calculations, identifying the spatial-temporal evolution characteristics of the gravity field in the study area. The relationship between seismic activity and gravity change has long been a topic of interest. The time-varying gravity field is a fundamental physical field that reflects the migration of mass and directly represents the internal tectonic movements of the Earth and surface mass redistribution. The link between earthquakes and gravity changes is primarily related to tectonic movement and variations in mass(density)within the Earth’s interior.

By examining gravity field changes at half-year and one-year scales and analyzing gravity profile images in relation to geological structures, this paper explores the characteristics of gravity field variations in Urumqi and its surrounding areas. To effectively separate gravity anomalies at different depth levels, wavelet multi-resolution analysis is employed to decompose the gravity field anomalies, distinguishing regional from local anomalies in the study area. Specifically, the wavelet multi-scale analysis method is applied to process gravity field dynamic data from 2019-2020, 2020-2021, and 2021-2022. This method helps isolate and interpret abnormal signals in the gravity field, improving the reliability of earthquake precursor gravity anomalies.

The gravity source characteristics provide insight into the physical property changes of the crust. In this study, the “equivalent source” inversion model is used to determine the dynamic characteristics of the crust’s apparent density. The multi-period gravity point values obtained through the adjustment method serve as input data for the equivalent source apparent density change model in the study area.

The results indicate that the gravity field in the study area exhibits clear zonation, with predominant negative changes and alternating positive and negative gravity anomalies. The wavelet gravity details show that the anomaly areas align with geological structures, and the estimated source depth, as determined by the power spectrum, is consistent with the Crust1.0 model. The inversion of the flow gravity data reveals the variation characteristics of the crust’s equivalent apparent density, which correlate well with the time-varying gravity field. Multi-scale decomposition of gravity anomalies at different depth levels further illuminates the physical property changes of the crustal medium, as reflected by the equivalent source density model. These findings, when combined with the regional tectonic background and seismic activity, offer valuable insights. The research presented in this paper provides a foundational understanding of gravity field trends in Urumqi and its surrounding areas, contributing to future predictions of gravity field changes in the region.

In this paper, based on microgravity time-varying signals, the gravity field and underground medium density change of Hutubi gas storage were simulated and calculated, and the response relationship between gravity change and injection-production pressure was analyzed. By using the 7 phases of mobile gravity data of Hutubi underground gas storage, adopting the classical adjustment method and selecting the absolute gravity points of HKPN, HKPS and Urumqi(BJ00) and Shihezi gravity point(BJ06) of CMONOC around the gas storage area as the calculation basis, the relative gravity variation of each monitoring point in the study area was obtained with the precision ranging (3~5)×10^-8m/s² for each point in each phase. Combined with the relevant data of gas storage injection-production pressure, the response relationship image between the spatial-temporal variation characteristics of gravity field and injection-production pressure in this area was acquired. The research shows that the gravity change in the entire survey area exhibits zoning characteristics. The gravity change in the outer area of the gas storage south of Hutubi Fault is relatively small, and the gravity change in the gas storage area increases and decreases alternately. Especially in the east side of the reservoir area, the gravity change shows obvious characteristics of decreasing in spring and increasing in autumn, which causes the natural gas in the gas storage to basically drop to the lowest in March, thus resulting in the minimum internal stress in the gas storage. According to the theory of crustal stress equilibrium, when the pressure inside the gas storage tends to increase or decrease, the stress outside the gas storage will be adjusted correspondingly. When the gas injected into the gas storage spreads between the rocks and their gaps in the gas storage, it will exert a certain pressure on the rocks, causing the medium density in the underground gas storage cavity to vary in different degrees, thus resulting in the changes in the gravity values of the surface measuring points in the gas storage area. Finally, based on the dynamic change data of gravity field observed on the surface of Hutubi underground gas storage, the constraint of depth weighting function was added in the calculation process to eliminate and weaken the multi-solution and skin effect, and the compact gravity inversion algorithm of spatial distribution of underground density variation anomaly body was adopted to simulate and calculate the underground material density change image of Hutubi gas storage and the morphological structure distribution characteristics inside the gas storage. In this paper, according to the structural framework of about 1km/layer in Hutubi gas storage, all slices are constructed in the vertical direction of 1km to the crust, and a total of 9 layers are cut into them. That is, they are divided from the surface to the interior of the gas storage from 0 to 9km. Based on the change amount of gas injection and production in Hutubi gas storage, combining with the density images of underground media in different periods, it can be clearly seen that the internal cavity shape distribution inside the gas storage is irregular, so the stress on each point in the gas storage will be uneven, resulting in different density changes of the medium in different depths. The density distribution of underground medium in this gas storage varies with time, and the density variation is relatively different, but it has a certain change rule. Most density variation images show four quadrant distribution characteristics, especially at the depth of about 3000~4000m of the gas storage, where the migration degree of underground medium substances is the largest, resulting in the largest density variation in this area, with the maximum density variation of about 0.7kg·m^-3. At this stage, the gas storage is just at the peak points of gas injection and production, that is, the maximum and minimum peak points of stress. In addition, the density change image has showed that the internal structure of the gas storage is in NW-SE direction, which is basically consistent with the geological structure distribution characteristics of Hutubi gas storage. Therefore, using gravity data, the structural form of Hutubi underground gas storage and the whole process of medium density changing with injection-production pressure can be clearly explained.

On Jan. 19, 2020, a magnitude 6.4 thrust earthquake occurred in Jiashi County, Xinjiang Uygur Autonomous Region, and the seismogenic structure is the Keping Fault. The epicenter of the earthquake is located inside the gravity monitoring network, which covers more than 90 gravity monitoring points from Aksu and Kuche to Kashgar and Wucha in the west, Taxkorgan in the south and Hetian area in the southeast. In this paper, the high-precision gravity measurement data in the western margin of the Tarim Basin from 2013 to 2020 before and after the earthquake are used and three absolute gravity measurement points at Kuche, Taxkorgan and Wushi are taken to provide space-time gravity reference constraint. Then, the test board method is used to carry out the field source resolution test, and combined with the theoretical gravity anomaly value of actual measurement points obtained by the gravity forward modeling method, the field source model parameters are obtained by the inversion method. Then, in light of “seeking the source by field and combining the field and source”, using the surface repeated gravity observation data, the point value sequence obtained based on the Bayesian gravity adjustment method, and the field source inversion method for the time-varying gravity signal, the paper evaluates the basic principle of equivalent source inversion method and the field source monitoring capability of the research area. The actual repeated gravity observation data are tested and inversed to obtain spatial and temporal variation characteristics of gravity field sources, as well as the dynamic variation of regional gravity field sources and the structure characteristics of apparent density of multi-period field sources before and after the earthquake in the study area in the last 10 years. Finally, the variation process of gravity field in the seismogenic tectonic area of the 2020 Jiashi magnitude 6.4 earthquake is analyzed and discussed in combination. The study concluded that the gravity survey network on the western margin of the Tarim Basin has a good ability to distinguish field source parameters around the epicenter of the Jiashi M_S6.4 earthquake, but its ability to monitor the interior Tarim Basin between the tectonic system on the west side of Hetian and Aksu is relatively weak. The significant gravity change before the Jiashi M_S6.4 earthquake started in 2017. The apparent density change showed a regional increasing trend as a whole, and the morphology first showed the EW orientation and gradually turned to the NEE orientation, which is consistent with the structural direction of the Keping fault system. The apparent density change trend weakened in 2019. After the earthquake, the apparent density demonstrated a NEE-directed decrease. Before and after the earthquake, the apparent density of the field source increased from positive to negative, and after the earthquake, this apparent density change was more consistent with the tectonic trend and extended to the entire Keping fault system, indicating that the field source change signal obtained from gravity monitoring is closely related to the seismic event and the structure-controlled field source environment change. After the Jiashi M_S6.4 earthquake, the apparent density of the field source decreased, which was consistent with Keping tectonic system. The lower apparent density appeared in the area from the epicenter of the earthquake to Atushi, which may be related to the redistribution of fluid material in the earth’s crust caused by the rapid isostatic adjustment of crustal material near the fault after the earthquake. However, the gravity data observed in April 2020 may still contain the coseismic effect information of the earthquake. The research methods and results of this paper can provide valuable reference for the study of source characteristics of time-varying gravity field and the analysis and interpretation of seismic gravity precursor signals, and also have important indicative significance for understanding the crustal tectonic activity patterns around the seismogenic zone and fault zone.

Four-component borehole strainmeter (FCBS) is one kind of high-precision borehole strain observation instruments invented in China. As a kind of near-surface deformation observation instrument, FCBS is also easily disturbed by the external environment factors. As a common factor, pumping has significant influence on FCBS observation. Existing studies mostly identify the pumping interference from the perspective of observation curve morphology, relatively few studies focus on its interference mechanism. In order to truly capture earthquake precursor information, it is necessary to study the interference mechanism. In recent years, RZB-3 type FCBS at Tai'an seismic station has been seriously affected by pumping, so it is necessary and also feasible to study the interference mechanism of pumping. Since the influence of pumping interference on borehole strainmeter is common, this work would be very practical and be used for reference by other borehole strain observation stations.
We find that the original observation curves and observed surface strain, shear strain from RZB-3 type FCBS at Tai'an seismic station have the characteristics of synchronous change with the borehole water level, in which the linear correlation coefficient between the two observed shear strain curves and borehole water level reached 0.70 and 0.82 respectively. We further find that the principal strain direction of borehole and borehole water level after normalization meet the nonlinear function as y=1.217arctan(x)^0.224-0.284. The above phenomenon indicates that the observation of RZB-3 type FCBS at Tai'an seismic station is significantly affected by the borehole water level, and the influence is more obvious and the gradient is larger at the stage of low water level. Pumping interference often appears in low water level stage and changes the rock pore pressure state. Statistics show that pumping interference affects the borehole strain state.
To investigate the interference mechanism of pumping to RZB-3 type FCBS at Tai'an seismic station, we take a known pumping as an example, in which we study the principal strain state of the borehole in three periods of normal pumping, interruption of pumping and resuming pumping respectively. During each period, we solve 3 parameters of the principal plane strain state, i.e. the maximum principal strain rate, the minimum principal strain rate and the maximum principal strain direction from four observation equations of FCBS by nonlinear iterative least squares algorithm. On the other hand, concentrated load model (CLM) is used to simulate the mechanical mechanism of pumping. Firstly, the depth of FCBS relative to pumping source and the concentrated load at pumping source are inversed, then, the strain state surrounding the pumping well, including the state at RZB-3 borehole, is simulated by forward modeling. By comparing these results, we find that:
(1)The concentrated load at pumping source inversed by CLM during periods of normal pumping and resuming pumping are both located at or near the bottom of the pumping well, which is consistent with the actual situation, indicating that mechanism and degree of the influence of pumping on borehole strain are well simulated by CLM.
(2)The observed strain state is consistent with the simulation result of pumping interference by forward modeling, indicating that the principal strain state of borehole calculated based on observation of FCBS reflects the true strain state of borehole under different pumping states.(3)The inversed concentrated load at pumping source during pumping periods is significant greater than the load of the pumped water, indicating that the pumping process has more significant influence on the pore pressure of rocks than the load of the pumped water.
Even though CLM is an approximate simulation since it's based on some elastic assumptions, the interference mechanism of pumping on RZB-3 type FCBS at Tai'an seismic station is well explained, which is maybe very helpful for studying the influence of pumping interference on other deformation instruments, locating the unknown pumping source and studying the characteristics of pore pressure of rocks.

Following the 11 March 2011 Japan M_W9.0 earthquake, frequent moderate and small events occurred on the Yishu fault zone and its either side. Using continuous GPS data and a sliding block model, this work studies the relationship between the energy release of these shocks and the block relative motion of either side of the Yishu fault zone. The results show that(1)the equivalent magnitude M from released energy and the two blocks' relative motion are well correlated when earthquakes are selected in a retrieval circle(whose center is the midpoint of the Yishu fault zone)with a radius of 250~500km and using a sliding time window of 3~10 months. The best correlation coefficient between M and the two blocks' relative motion is 0.74 and the T test shows a significant linear correlation between them.(2)Spatial distribution of the correlation coefficients shows that the relative motion of the blocks on both sides affects the energy release in the area from the north part of Yishu fault zone to the Jiaodong Peninsula area and southwest Shandong-Henan border area obviously.(3)Since June 2014, the relative motion of the two blocks on both sides of the Yishu fault zone presents a wave of change, which may be an expression of the accumulation of seismic strain energy in the Yishu fault zone and its two sides. The linear relationship between the equivalent magnitude M from released energy and two blocks' relative motion V can be fitted by linear equation M=0.51*V+3.9, showing that strain energy accumulation could be released by the moderate and small earthquakes in a timely manner, which may favorable to delay the seismic risk in the study area. It also shows, on the other hand, that earthquake energy was not released so completely in the study area since the end of 2015 to 2016, which is likely associated with the Changdao earthquake swarm in 2017.

Mud volcano is a kind of structural geological phenomena under certain hydrogeological environment and can bring plenty of valuable information to the ground when it erupts, therefore, many researchers call it as "Heaven granted well" whose depth can be up to 12km. Mud volcanoes in Xinjiang are distributed in the central-west region of North Tianshan, and five of them are representative, namely, Horgus, Dushanzi, Wenquan, Poplar valley, and Sailetike. We tested the gas, fluid and solid components of these mud volcanoes through investigations and studies of topography and geomorphology, geological and hydrogeological conditions, and mud debris characteristics, and preliminary obtained the origin of these mud volcanoes based on geochemical features. Finally, the paper describes briefly that the continuous enchancement of regional crustal tectonic stress can not only give rise to the seismogenesis and earthquake occurrence, but also break the original cycle of mud volcano to bring about significant activity, therefore, the two have a certain homology relationship.

In this paper, the approach to the understanding of seismic tectonic environment in moderate and strong earthquake areas are discussed through the antithetic analysis of shallow and deep structures, macro-microstructural analysis, and analysis of both historical and recent seismic data. Taking the Liu'an-Huoshan seismic risk area as an example, the authors have carried out a three dimensional analysis of the area, and predicted the potential location of future earthquake and its corresponding parameters including focal depth, magnitude, and the attenuation direction of the isoseism. The results of this study indicate that the NE-, NW- and nearly E-W-trending faults in this area exhibit obvious activities. The junctures of these 3 sets of faults are prone to stress concentration, making up the seismogenic background for future moderate strong earthquake in this area. The most possible location for future earthquakes is the western side of the Funanshan Mountain, the juncture between the Luo erling-Tudiling, Meishan-Longhekou and Xiafuqiao-Hujiahe Faults. The seismogenic model for this area is constructed on the basis of analysis of seimotectonic environment by referring to the interpretation of remote sensing images, the results of seimogeolo~gic investigation and the Suizhou to Halqin Qi geoscience transect that obliquely passing through this area. Based on the focal depth, the features of isoseimal lines and the migration regularity of the past seismic events occurred in this area, the focal depth of the future earthquake is postulated to be 12～15km, and the isoseism will be equidimensional in shape. It is proposed that the Liu'an-Huoshan seismic risk area is obviously active. As the area is broken, however, energy is difficult to be accumulated and large earthquake is difficult to be generated. It is suggested, therefore, that the future earthquake will be a moderate-strong earthquake.m ,andtheisoseismw

The Three-Gorges well network is the first well network in China established specially for the purpose of monitoring the groundwater precursors of reservoir-induced earthquake. The basic consideration of the establishment of this well network is based on the fact that the seismic event of certain magnitude induced by the storage of reservoir may cause the changes of stress and strain states of the aquifer, as well as the corresponding pore water pressures. The number and spacing of the wells are determined according to the magnitude of earthquake(M_S), the length of seismogenic fault(L)and the variation range of stress strain field(R). The selection of well locations is based on the groundwater behaviors sensitive to earthquakes. Such peculiar tectonic sites as the termination, inflection and junction of fault zones are selected for well location. The depth and structure of the wells are decided according to the requirement that the well may reveal well enclosed confined aquifer and minimize the influence of surface water and hydro atmospheric factors on the premise of limit funds. According to the afore mentioned considerations, 4 wells are drilled at the dam site and 4 wells at the head of the Three-Gorges Reservoir. The depths of the wells are between 100～ 200m, and all the wells expose well enclosed confined aquifer. Primary observations show that the arrangement of the Three-Gorges well network and the establishment of the observation wells are relatively successful. They form a good base for monitoring the precursor of reservoir-induced earthquake.

Based on studying of satellite and aerial photographs, we made field investigations and sampling to the fault which occurred in bredrock area of northern Dabie mountain. The particular emphasis is laid on research of dislocation geomorphology and deformation material, and analysing the time space characteristic of seismological activity. We obtained information of the fault including its active time mode, and relation to earthquakes. It offers an example for research way to active behavior of the fault in bedrock area.

Since having historical records, there have been many times middle or small earthquakes occurred along the Susong-Zongyang fault, southwest area of Anhui province. This paper gives a synthetic study on the fault by means of macro-microscopic structural analysis, dating of the deformational materials, and combing with a series of seismic safety evaluation of the enginnering sites in this area. Based on the aforementined work, the authors revealed the geological background of middle or small earthquakes along the fault, and forecased initially the level of seismic acitvity nearby the fault in future. It offers an example to evaluating fault's active behaviour in the areas of lower seismicity.

Based on orientated sampling of deformation prod ucts in Juxian Zhaoxian～Suqian Xiaodian of the Tancheng-Lujiang fault zone, undisturbing and indurating sampling, the micorscopic ob-servation has been conducted, along with results of rock-breaking test and microsopic analysis.The authors come to conclusion of microscopic marks of stick slippage,reprsentative of kinetic characteristics of the fault zone. Outlined some problems in this regard have been discussed aswell.