Fault Zone In China Research Articles

Emission of Rn and CO2From Soil at Fault Zones Caused by Seismic Waves

AbstractIn the search for precursors to earthquakes, correlation has been found between geochemical characteristics of soil gases and seismic activity. In this paper we present evidence that seismic waves can trigger emission of soil radon (Rn) and carbon dioxide (CO2). An active experiment was performed in two fault zones in China, the Annighe fault in Sichuan province and the Xiadian fault in Heibei province. An active seismic source was used to generate seismic waves at 10 m depth in wells within bedrock. Rn and CO2detectors were placed around the wells at a distance of ∼1 m for observing the effects of the seismic waves on the emission of the gases. The observations confirm that the seismic waves have a significant and direct effect on the concentration and flux of soil radon and carbon dioxide. When the seismic events were triggered, the observed concentrations of Rn and CO2immediately increased and reached peak values within 5–50 min and 30–60 min, with corresponding increases of Rn and CO2concentrations by 10.5%–238.7% and 3.1%–54.1%, respectively. The measured concentrations and flux of CO2and Rn after the passage of the seismic waves showed strong correlation, confirming the suggestion that CO2is the carrier gas for Rn. To the best of our knowledge this is the first direct, in‐situ measurement of gas emission caused by the passage of seismic waves and provides important constraints for better understanding of geochemical earthquake precursors.

Effects of the 2011 Mw 9.0 Tohoku-Oki Earthquake on the Locking Characteristics and Seismic Risk of the Yishu Fault Zone in China

To ascertain the 2011 Tohoku-Oki Mw 9.0 earthquake’s impact on the stability of the Yishu fault zone, this study inverts the fault locking degree and slip rate defect distribution of the Yishu fault zone using GPS horizontal velocity field data covering the period from 1999 to 2009 and from April 2011 to 2019. This is based on the block negative dislocation model. Combined with the b value and strain field characteristics, the properties of deformation of the Yishu fault zone before and after the earthquake are comprehensively analyzed. The results show that before the 2011 Tohoku-Oki Mw 9.0 earthquake, the locking degree and depth of the northern segment of the Yishu fault zone were higher, while the locking depth of the southern segment of the fault was shallower. The 2011 Tohoku-Oki earthquake produced different coseismic effects on the southern and northern sections of the Yishu fault zone. The extension on the southern section and compression on the northern section caused the strain release in the southern sections of the Yishu fault zone following the earthquake. After it, the regional locking degree of the southern section of the Yishu fault zone was relieved. However, the locking degree of the northern segment of the fault zone was still high and the depth was deep, at about 26 km. In addition, the northern section of the Yishu fault zone was a section with an abnormally low b value and small earthquakes in the northern segment are sparse at present. The coseismic compression of the northern section caused by the 2011 Tohoku-Oki earthquake is conducive to its locking and easily accumulates stress, so it is necessary to pay attention to its seismic risk.

The Contribution of Petroleum Charging Episodes to Different Strike-Slip Fault Zones in the Shunbei Area, the Tarim Basin, NW China

In recent years, newly discovered ultra-deep fault-karst reservoirs in the Shunbei area of the Tarim Basin have greatly increased the prospectivity of the basin and become a hotspot for further hydrocarbon exploration. In this study, the diagenetic sequences of the Lower-Middle Ordovician reservoir were established through observation of thin sections under transmitted light, reflected light, and cathode luminescence. The hydrocarbon charge history in the Shunbei area was reconstructed and associated with a series of diagenetic events using fluid inclusion microthermometric measurements combined with one-dimensional basin modeling. The results show that the Shunbei area has experienced three hydrocarbon charging episodes in total, in the late Caledonian, late Hercynian, and late Himalayan. Finally, the relationship between measured QF-535 factors and the API gravity of crude oil was used to quantify the level of contribution of each of the petroleum charging episodes to the No. 1, No. 5, and No. 7 fault zone reservoirs. The contribution of early hydrocarbon charging episodes gradually increases from west to east in the Shunbei area. This increase was driven by different tectonic events throughout geological history and the subsequent evolution of paleo-structural patterns. This study has a significant impact on marine carbonate reservoir evaluation in strike-slip fault zones in China.

Landslide Susceptibility Mapping along the Anninghe Fault Zone in China using SVM and ACO-PSO-SVM Models

Abstract In the present study, a hybrid machine learning model was designed by integrating ant colony optimization (ACO), particle swarm optimization (PSO), and support vector machine (SVM) algorithms. The model was used to map the landslide susceptibility of the Anninghe fault zone in Sichuan Province, China. Based on this, 12 conditioning factors associated with landslides were considered, namely, altitude, slope angle, cutting depth, slope aspect, relief amplitude, stream power index (SPI), gully density, lithology, rainfall, road density, distance to fault, and peak ground acceleration (PGA). The overall performance of the two resulting models was tested using the receiver operating characteristic (ROC), area under the ROC curve (AUC), Cohen’s kappa coefficient, and five statistical evaluation measures. The success rates of the ACO-PSO-SVM model and the SVM model were 0.898 and 0.814, respectively, while the prediction rates of the two models were 0.887 and 0.804, respectively. The results show that the ACO-PSO-SVM model yields better overall performance and accurate results than the SVM model. Therefore, in conclusion, the ACO-PSO-SVM model can be applied as a new promising method for landslide susceptibility mapping in subsequent studies. The results of this study will be useful for land-use planning, hazard prevention, and risk management.

Hydrogeochemical Characteristic of Geothermal Water and Precursory Anomalies along the Xianshuihe Fault Zone, Southwestern China

Hydrogeochemical changes in association with earthquakes are considered as a potential means of identifying earthquake precursors. The Xianshuihe fault zone (XSHF) is considered one of the most active seismic fault zones in China; 43 hot springs were sampled and analysed in the laboratory for major elements, silica, stable isotopes (δD and δ18O) and strontium isotopes were investigated from 2008 to 2021. The meteoric water acted as the primary water source of the hot spring in the XSHF, and recharged elevations ranged from 1.9 to 4.8 km. The geothermometers method was used to estimate the region of thermal storage temperature and its temperature between 8 and 142 °C. And the circulation depth ranged from 0.1 to 6.9 km. Most of the hot spring water was immature water with a weak degree of water-rock reaction. However, the degree of water-rock reaction and the depth of hot spring water circulation were high in part of the Kangding and Daufu segments, which also had the highest reservoir temperature and the most frequent strong earthquakes. Temporal variations of hydrogeochemical showed that Na+, Cl− and SO42− decreased obviously following the 12 May 2008 Wenchuan Ms8.0 and existed abnormal value fluctuations from the 20 April 2013 Lushan Ms7.0 to 22 November 2014 Kangding Ms6.3 occurred and after 20 July 2017 returned to the normal levels. And the ion concentrations in hot springs increased by 5% to 35% three months before 22 November 2014 Kangding Ms6.3 with the obvious precursor anomaly. Hydrogeochemical anomalies could be useful for predicting an earthquake in the study area.

222Rn radioactivity in urban waters of fault zone in China: dose rate and risk assessment

222Rn radioactivity in urban waters of fault zone in China: dose rate and risk assessment

Temporal variations in stable isotopes and synchronous earthquake-related changes in hot springs

Earthquake-related hydrogeochemical changes are considered a possible means of identifying earthquake precursors. This work investigated the time series of hydrogen and oxygen stable isotopes at three hot springs in Kangding with different temperatures, namely, the Erdaoqiao, Longtougou, and Guanding hot springs, located in the Xianshuihe fault zone, one of the most active seismic fault zones in China. The hot springs were observed with a sampling frequency of 3 or 4 days for one year. The results showed that the three hot springs were recharged by meteoric water, and there was a slight water–rock interaction at the Longtougou hot spring. The different isotopic compositions of the three hot springs were related to the recharge and groundwater circulation environment. Temporal anomalies in the stable isotope values at the three hot springs occurred synchronously; these anomalies were closely related to the 2019 Mw 5.8 Changning earthquake, indicating possible earthquake-related changes. Moreover, the amplitudes of stable isotope variations at the three hot springs were closely related to the seismic energy density, and the background isotopic changes were related to the water temperature and flow. These findings reflect the hydrological cycle processes of geothermal water in the Kangding geothermal area on the eastern margin of the Tibetan Plateau. Simultaneously observed temporal variations in hydrogen and oxygen stable isotopes among multiple hot springs may have relevance for distinguishing earthquake precursors.

Numerical Analyses on the Stability of a Deep Coalmine Roadway Passing through a Fault Zone: A Case Study of the Gugui Coalfield in China

Massive deformation often occurs when deep coalmine roadways pass through a fault zone due to the poor integrity of rock mass and high tectonic stress. To study deformation characteristics of the surrounding rock in the fault zone of a coalmine, a roadway passing through the FD1041 fault zone in China’s Gugui coalfield was investigated in this research. The geo-stress characteristics of this fault zone were analyzed based on the Mohr failure theory. Furthermore, a three-dimensional model for the experimental roadway in the FD1041 fault zone was built and calculated by a numerical program based on the distinct element method. Stability conditions of the roadway, using several types of support methods, were calculated and compared. Calculation results indicated that pre-grouting provides favorable conditions for the stability of a roadway in a fault zone. Finally, an optimized support strategy was proposed and implemented in the experimental roadway. Monitored results demonstrated that the optimized support strategy is appropriate for this fault zone.

Study of Characteristics of Fault Slip and Induced Seismicity during Hydraulic Fracturing in HDR Geothermal Exploitation in the Yishu Fault Zone in China

Hot dry rock (HDR) geothermal energy has become promising resources for relieving the energy crisis and global warming. The exploitation of HDR geothermal energy usually needs an enhanced geothermal system (EGS) with artificial fracture networks by hydraulic fracturing. Fault reactivation and seismicity induced by hydraulic fracturing raise a great challenge. In this paper, we investigated the characteristics of fault slip and seismicity by numerical simulation. The study was based on a hydraulic fracturing project in the geothermal field of Yishu fault zone in China. It revealed that fluid injection during hydraulic fracturing can cause the faults that exist beyond the fluid-pressurized region to slip and can even induce large seismic event. It was easier to cause felt earthquakes when hydraulic fracturing was carried out in different layers simultaneously. We also examined the effects of the location, permeability, and area of the fracturing region on fault slip and magnitude of the resulting events. The results of the study can provide some useful references for establishing HDR EGS in Yishu fault zone.

Description of the reservoir along strike-slip fault zones in China T-Sh oilfield, Tarim Basin

The reservoir depth of T-Sh oilfield in Tarim Basin is more than 7500 m, which is a typical deep carbonate fault-controlled reservoir. The S-1 and S-5 fault zones experienced multi-stage tectonic movements and developed complex fault-fracture systems. Based on geometry and dynamics, the evolution characteristics of faults are analyzed; the permeability of strike-slip faults in the middle and lower Ordovician carbonate strata drilled through in S-5 fault zone is studied by comprehensively using core observation, imaging logging, 3D seismic data, and drilling historical data, taking wells F-1 and F-10 as examples. It is found that the fault-fracture system is the main reservoir space and fluid migration channel in the reservoir. A large mud loss will occur when drilling high permeability faults. High production can be obtained after conventional well completion, otherwise, it is difficult to get production. In this paper, slip tendency coefficient is used to quantitatively characterize the permeability of fractures in T-SH ultra-deep reservoir. Based on the one-dimensional geomechanical model and three-dimensional geological structure model of typical wells, the slip tendency coefficients of different parts of the fault-fracture system are calculated using finite element numerical simulation method. Compared with the historical data of drilling in S-1 and S-5 fault zones, it is found that the slip tendency coefficient is positively correlated with mud loss. The results show that the critical slip tendency coefficient of the S-5 fault zone is 0.3, and that of the S-1 fault zone is 0.2. This study provides a new idea and method for the prediction of geological desserts and well trajectory design in the T-Sh reservoir.

Evaluation of favourable hot dry rock areas in the east of the Yishu fault zone in China

Hot dry rock (HDR) geothermal resources have great development potential and prospects, owing to their wide distribution and high thermal storage temperature. HDR resources are abundant in China, but their exploration and exploitation remain in the early stages. The Yishu fault zone in Shandong Province in eastern China is in a high-temperature geothermal zone of the Pacific Rim. Three craters and 15 hot springs are in this area, which possesses abundant geothermal resources and favourable conditions for the occurrence of HDR resources. Nevertheless, HDR resources in this area have not been studied in detail, and the index-evaluation system for HDR is still imperfect. In this paper, five index layers are selected, including: the gravity and magnetic fields, geothermal field, tectonic activity, reservoir and cover characteristics, and remotely sensed features. Thirteen index elements were also selected as evaluation factors. In combination, these index layers and index elements have established a favourable evaluation index system for HDR resources in this region, and the analytic hierarchy process has been used to determine the weight of each factor. Then, the GIS spatial analysis function is used to carry out spatial superposition analyses for each index element, and finally the distribution characteristics of HDR resources east of the Yishu fault zone were determined, with four favourable selection areas being delineated. The occurrence conditions of HDR resources are analysed in detail with evaluation indexes. It is believed that HDR resources are closely related to neotectonic movement, volcanism and rocks with high heat-generation rates. Searching for areas with geothermal anomalies is indispensable for the evaluation of HDR resources. This study provides a basis for the exploration and development of HDR resources in the region, and it can also provide a reference for similar work in other parts of the country. KEY POINTS A set of evaluation indexes to determine favourable areas for HDR resources, including gravity, geothermal field, geological structure and crustal stability, heat storage and heat cover and features on remotely sensed images, is established. East of Yishu fault zone, there is a great potential of HDR resources, with an area of 19 399 km2 of favourable and more favourable areas, accounting for approximately 38.8% of the total area. HDR resources are likely closely associated with neotectonics, igneous activity, geothermal anomalies and rocks with a high heat-generation rate such as granites.

A case study of water inrush incident through fault zone in China and the corresponding treatment measures

In 2010, a water inrush accident through a fault with a high flow rate occurred at Tianzhuang coal mine in Jining, Shandong Province, China, which was subject to the fault excavation. Grouting is an important treatment method before and after water inrush accidents. In this paper, the evolution of this water inrush accident is studied, and the effective treatment method is presented. The obtained results indicate that groundwater from Ordovician limestone aquifer 28.5 m below the floor flowed into the roadway through the fault zone. Results also show that this water inrush through the fault zone can be divided into a flow rate steady increase phase, a rapidly increase phase, a decrease phase, and a steady phase. The first two phases resulted from permeability increase of the fault, which was caused by seepage failure, and water level of the aquifer led to last two phases. Additionally, grouting using the ground borehole successfully controlled this water inrush accident, and it is proven to be a valid method.

Coulomb Stress Evolution History as Implication on the Pattern of Strong Earthquakes along the Xianshuihe-Xiaojiang Fault System, China

Coulomb stress accumulation and releasing history and its relationship with the occurrence of strong historical earthquakes could deepen our understanding of the occurrence pattern of strong earthquakes and hence its seismic potential in future. The sinistral strike-slip Xianshuihe- Xiaojiang fault zone (XXFS) is one of the most dangerous fault zones in China, extending 1 500-km-long from the central Tibetan Plateau to the Red River fault zone. There are 35 M≥6.5 historical earthquakes occurred since 1327, hence it is an ideal site for studying the Coulomb stress evolution history and its relationship with the occurrences of strong earthquakes. In this study, we evaluated the Coulomb stress change history along the XXFS by synthesizing fault geometry, GPS data and historical earthquakes. Coulomb stress change history also revealed different patterns of historical earthquakes on different segments of the XXFS, such as characteristic recurrence intervals along the Salaha-Moxi fault and super-cycles along the Xianshuihe fault. Based on the occurrence pattern of past historical earthquakes and current Coulomb stress field obtained in this study, we suggest positive ΔCFS and hence high seismic potential along the Salaha-Moxi fault and the Anninghe fault.

Genetic diversity and population structure in cherry (Cerasus pseudocerasus (Lindl). G. Don) along Longmenshan Fault Zones in China with newly developed SSR markers

Chinese cherry (Cerasus pseudocerasus (Lindl). G. Don), native to China, is a commercially valuable fruit crop with extensive morphological diversity along Longmenshan Fault Zones, a region adjacent to the Qinling and Hengduan Mountains. In this study, we developed simple sequence repeat (SSR) markers from its own genome to comprehensively investigate the genetic variation of Chinese cherry in this center which is well-known by frequent geological activities and high levels of biodiversity. A total of 33,263 microsatellite sites were identified from the C. pseudocerasus genome, among which 30,148 SSR markers were designed. Of these markers, two hundred primer pairs were evaluated, and finally 20 polymorphic markers were selected to assess the genetic diversity and population structure of 15 representative natural populations (214 total individuals) in the region. The results revealed a moderately high genetic diversity in C. pseudocerasus (Na=7.00, He=0.62, PIC=0.59, I=1.26). A reduction of genetic variation, heterozygote excess and domestication bottleneck were detected in landrace populations (Na=4.00, He=0.41, Ar=1.87, FIS=−0.11) when compared with the wild ones (Na=6.95, He=0.65, Ar=2.49, FIS=0.35).The mantel test showed no significant correlation between geographic and genetic distance (r=0.581, P=0.08). Moderate differentiation and frequent gene flow were detected among all populations (FST=0.0659, P=0000, Nm=3.5436). Nevertheless, a clear structure and relatively high differentiation (FST=0.1173, P=0000, Nm=1.8813) were observed between most wild and landrace populations according to the STRUCTURE clustering and AMOVA analyses. The newly-developed SSR markers in our study exhibited high efficiency and can be utilized in further studies on this species and relatives. Meantime, the comprehensive assessments of genetic diversity of Chinese cherry resources in the biodiversity center have provided us basic genetic knowledge of this species, and this information will be very useful to policy makers on cherry breeding plan and species conservation.

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Self-Cooling Solar Cells: Glass overlay boosts efficiency and lengthens life of solar cells; Thin Film Sorts and Concentrates Sunlight; The Universe's UV Light Crisis; A Meta-Mirror for Nonlinear Optics; One-Atom Optical Switch; Measuring the Smallest Force; PV Inverter Growth Booms in China; Turning Laser Physics Upside Down; Using Lidar to Map Fault Zones in China.

Crustal motion of Chinese mainland monitored by GPS

To measure and monitor the crustal motion in China, a GPS network has been established with an average side length of 1 000 km and with more than 20 points on the margins of each major tectonic block and fault zone in China. Three campaigns were carried out in 1992,1994 and 1996, respectively by this network. Here we present, for the first time, the horizontal displacement rates of 22 GPS monitoring stations distributed over the whole China and global IGS stations surrounding China, based on these GPS repeated measurements. From these results by GPS, we have obtained the sketch of crustal motion in China.

The orogenic movement of the Main Mobile Fault Zone in China

The orogenic movement of the Main Mobile Fault Zone in China

Microstructural features of deformed rocks across the brittle-ductile transition

Based on the investigation of fault rocks from several major fault zones in China, this paper deals with the microstructural features of deformed rocks across the brittle-ductile transition and three types of coexistence of different deformation microstructures are summarized. These are: (i) Coexistence of different deformation microstructures of same mineral, for example, feldspar shows both brittle and ductile deformation features; (ii) Coexistence of different deformation microstructures of different minerals, for example, in same mylonite specimen quartz shows completely ductile deformation features while feldspar shows brittle deformation features; (iii) Coexistence of different deformation microstructures of same mineral at different scale, for example, feldspar shows ductile flow features without fractures under the optical microscope while quartz shows microfractures and “microcrashed zones” under TEM. The authors consider that these coexistence of different deformation microstructures should be helpful to study and understand the process of rock deformation across the brittle-ductile transition.

Geochemical characteristics of underground fluids in some active fault zones in China

This paper presents a study of tectonic activity in China by means of fluid‐geochemical methods. It is observed that deep fluids with characteristic chemical and isotopic compositions (high values of He and H2 and very low value of tritium) have migrated upward at some active faults. Many fluid‐geochemical anomalies were observed during periods of seismic activity, suggesting the usefulness of fluid‐geochemical methods for earthquake prediction. To properly select monitoring springs (or wells) and chemical components, local geological conditions have to be fully considered.

Structure and deformational character of strike-slip fault zones

Strike-slip fault zones observed either in the field or in model experiments generally consist of several subparallel faults which make these zones complicated in geometry and kinematics. The geometry of a strike-slip fault or shear zone is dependent on arrangement (pinnate or en echelon), on step (left step or right step), and on the rank )smaller faults within larger faults) of the subparallel fault. The relations and interactions of these three factors create a variety of dynamic circumstances and tectonic settings within the strike-slip fault zones. These include pull-aparts in the release area between subparallel faults, push-ups in the jogs where the subparallel faults overlap, and pivotal movements, or rotation, of single faults along the whole fault zone. Each kind of tectonic setting is in itself characteristic, each setting consists of many subtypes, which are controlled chiefly by the geometric parameters of the subparallel faults. One of the most important phenomena revealed in the field work is two different kinds of evolution of strike-slip fault zones: one is the evolution of a zone with a tensile component, which is related to the growth of rock bridges, and the other, of one with a compressional component, which develops by the destruction of rock bridges. In this paper we discuss, on the basis of recent research on four strike-slip fault zones in China, the essential characteristics of strike-slip faults and the possible causes of the observed structural phenomena. Attention is focussed on the deformation, development, and distribution of horizontal displacements within strike-slip fault zones.