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Abstract With the increase in mining depth and intensity, dynamic disasters such as rockburst in mines are becoming more severe. Deep resource extraction is characterized by a high in-situ stress geological environment, closely associated with geological dynamic disasters. However, there is currently no quantitative analysis method for the correlation between the two. In this study, an elastic energy density calculation method is employed, considering the dissipative effect of the self-weight stress field on the tectonic stress field. The remaining energy, referred to as impact energy, is used to classify the risk of coal seam impact, providing a computational method for rapid assessment of impact risk before mining production. The proposed calculation method is compared with 22 mine impact engineering practices in the literature, showing accurate predictions for 21 mines. Since measuring in-situ stress and coal seam physical and mechanical properties is a preliminary work in coal seam extraction, the comprehensive analysis of these data holds significant research and practical value.

With the increase in mining depth and intensity, dynamic disasters such as rockburst in mines are becoming more severe. Deep resource extraction is characterized by a high in-situ stress geological environment, closely associated with geological dynamic disasters. However, there is currently no quantitative analysis method for the correlation between the two. In this study, an elastic energy density calculation method is employed, considering the dissipative effect of the self-weight stress field on the tectonic stress field. The remaining energy, referred to as impact energy, is used to classify the risk of coal seam impact, providing a computational method for rapid assessment of impact risk before mining production. The proposed calculation method is compared with 22 mine impact engineering practices in the literature, showing accurate predictions for 21 mines. Since measuring in-situ stress and coal seam physical and mechanical properties is a preliminary work in coal seam extraction, the comprehensive analysis of these data holds significant research and practical value. [ABSTRACT FROM AUTHOR]

Obtaining higher-resolution and more realistic characteristics of tectonic stress fields is the goal of research into tectonic stress field simulations. In this study, a regional heterogeneous rock mechanics model was established on the basis of seismic, logging, and sample experimental data. The simulation results show that the minimum principal stress values in the lower Niutitang formation are between 25.0 and 120.0 MPa. The quantitative distribution prediction results for shale reservoir fractures based on the high-resolution tectonic stress field numerical model show that the fracture development zones in the Sangzhi block are mainly distributed near the fault, fold axis turning, and fold wing in an NE–SW orientation. There are two types of fractures developed in this region: shear fractures and tensile fractures. The shear fractures mainly developed near the NE–SW-oriented faults, with shear fracture rates ranging from 1 to 3, and the tensile fractures mainly developed in the southeast wing of the Wudaoshui anticline, with tensile fracture rates ranging from 1 to 2. The low fracture development zone is mainly located in the western slope of the block, with shear fracture rates and tensile fracture rates that are both < 1. [ABSTRACT FROM AUTHOR]

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The development of earth fissures in a certain area often has certain genetic correlations, which is called ‘group-developing phenomenon’ of earth fissures. So far, 41 earth fissures have developed in the Beijing area in the North China Plain. Surveys and exploration studies have shown that these earth fissures have a good correspondence relationship with the activities of the adjacent control faults. Accordingly, they can be divided into 9 zones. The mechanical analysis of these fissures groups reveals that they are roughly formed through 3 models, namely, ‘contemporaneous model’ (dip-slipping movement), ‘secondary model’ (strike-slipping movement) and ‘companion model’ (basin extension movement). The characteristics of this type (fault-controlled) earth fissures in combination with their distribution regularities in the area can be used to indicate that the distribution of subsurface tectonic stress fields is as a whole an extension of the NW-SE-trending, which is not completely consistent with the near E-W-trending extension of deep material migration. These analyses show that under the background of extensional deformation of the basin, the subsurface stress field characteristics of superficial formations are more complex, which not only embodies the movement form (unity) of the deep structure in whole, but also partially reflects the adjustability of the regional tectonic stress field.

By collecting focal mechanism solutions of earthquakes at different depths from Northeast Japan to Northeast China during 1957 to 2022, the joint iterative stress inversion method is used to calculate the tectonic stress field in the subduction zone and the tectonic stress field state in Northeast China. The results show that the shallow area of the Japan trench is not only affected by the subduction and extrusion of the Pacific plate, but also related to the extrusion of the North American plate. The deep source earthquakes in Northeast China are closely related to the long-term action of the trench subduction zone. The formation of the Changbaishan volcanic area has a great relationship with the thrust of the subduction zone. The seismicity of the subduction zone indirectly controls the formation and activity of the volcanic area in Northeast Asia. The principal compressive stress axis distributes in the NEE-SWW direction in the Yingkou area of Liaoning, while the principal tensile stress axis distributes in the NNW-SSE direction. Based on the results of the focal mechanism of shallow earthquakes in the volcanic area and its surrounding areas, it is believed that the current tectonic stress field in the northeastern volcanic area continues the overall structure of stress in the northeastern region, with the principal compressive stress axis in the NEE-SWW direction and the principal tensile stress axis in the NNW-SSE direction.

The mutual extrusion and collision between the Asia-Europe plate and the India plate led to the strong uplift of the Qinghai-Xizang Plateau, the squeezing of crustal material into the northwest and central and western parts of Yunnan, the intense geological tectonic activity and frequent geological disasters. In order to explore the influence of tectonic stress field characteristics on geological disasters, this paper uses regional structural analysis method, joint analysis method, conjugate shear joint method and water system line graph method to invert the tectonic stress field in the study area, to explore the control effect of various geological structures on geological disasters, and to propose corresponding countermeasures for tectonically induced geological disasters. The results show that the north-east, north-west and near-east-west faults and joint structures are developed around the Xiangyun Basin, and the study area has experienced at least three tectonic stress fields through the intersection of faults and joints and the water system line diagram method, and the maximum principal stress σ1 has successively transformed from the north-east to the north-west to the near-east-west. The fault structure indirectly induces geological disasters by controlling the evolution of the water system. In the area, rivers such as Sancha River and Juli River are mostly developed along the fault zone, and geological disasters such as landslides and collapses are mostly distributed along the slopes on both sides of the rivers. The multi-period activities of the geological structure enhance the density of the fracture network system of the rock and soil mass, resulting in the development of geological disasters. For the prevention and control of geological disasters induced by structure, the effect of engineering management is poor, and this paper puts forward the countermeasures of optimizing the site selection of construction area, relocation avoidance and group survey and group prevention. [ABSTRACT FROM AUTHOR]

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Abstract When evaluating strong ground motions and tsunamis from specified source faults, it is required that the input parameters, such as fault geometry, rake angle, and slip amount, do not deviate from those of a real earthquake. Recently, a regional three-dimensional (3D) tectonic stress field was used to estimate rake angles for mapped submarine faults with the Wallace–Bott hypothesis (WBH), the direction of fault slip was parallel to the resolved stress vector on a preexisting fault, and strong ground motions and tsunamis were simulated. However, this modeling technique has not been adequately validated. Additionally, it is necessary to examine how the stress field estimated from seismological data for a limited period (~ 10 years) can be used as a proxy for the long-term tectonic stress field. In this study, to provide such validation, we utilized two catalogs of focal mechanism solutions for earthquakes and compared the observed rake angles with those calculated from the regional 3D tectonic stress field with the WBH by fixing the fault strike and dip angles according to those from the focal mechanism data. The resulting misfit angles between the observed and calculated rake angles are generally small (ranging between − 30° and 30°), excluding several regions (e.g., the source and surrounding regions of the 2011 off the Pacific coast of Tohoku earthquake and swarm-like activities activated after the 2011 quake). We also confirmed that the calculated rake angles and classified fault types are consistent with geomorphologically and geologically evaluated types of faulting for major Quaternary active faults in the Kyushu district of southwest Japan. These results support the validity and effectiveness of estimating rake angles for a specific fault with known geometry from the above method and data, while also showing that close attention is needed to apply this method to, for example, seismically inactive regions where the inverted stress field includes significant uncertainties and/or near sites of recent and large earthquakes where the stress field has been perturbed. Graphical Abstract

Copyright of Acta Geoscientica Sinica is the property of Acta Geoscientica Sinica Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

When evaluating strong ground motions and tsunamis from specified source faults, it is required that the input parameters, such as fault geometry, rake angle, and slip amount, do not deviate from those of a real earthquake. Recently, a regional three-dimensional (3D) tectonic stress field was used to estimate rake angles for mapped submarine faults with the Wallace–Bott hypothesis (WBH), the direction of fault slip was parallel to the resolved stress vector on a preexisting fault, and strong ground motions and tsunamis were simulated. However, this modeling technique has not been adequately validated. Additionally, it is necessary to examine how the stress field estimated from seismological data for a limited period (~ 10 years) can be used as a proxy for the long-term tectonic stress field. In this study, to provide such validation, we utilized two catalogs of focal mechanism solutions for earthquakes and compared the observed rake angles with those calculated from the regional 3D tectonic stress field with the WBH by fixing the fault strike and dip angles according to those from the focal mechanism data. The resulting misfit angles between the observed and calculated rake angles are generally small (ranging between − 30° and 30°), excluding several regions (e.g., the source and surrounding regions of the 2011 off the Pacific coast of Tohoku earthquake and swarm-like activities activated after the 2011 quake). We also confirmed that the calculated rake angles and classified fault types are consistent with geomorphologically and geologically evaluated types of faulting for major Quaternary active faults in the Kyushu district of southwest Japan. These results support the validity and effectiveness of estimating rake angles for a specific fault with known geometry from the above method and data, while also showing that close attention is needed to apply this method to, for example, seismically inactive regions where the inverted stress field includes significant uncertainties and/or near sites of recent and large earthquakes where the stress field has been perturbed. [ABSTRACT FROM AUTHOR]

The macroscopic structural fractures (joints) and geostress distribution characteristics of coal reservoirs are important factors affecting the exploitation of coalbed methane (CBM). In this study, the joints in the sedimentary strata of the Dahebian block in Liupanshui area, Guizhou Province were investigated. Directional coal samples were collected for observation and statistical analysis of coal microfractures, the paleotectonic stress fields of the study area were reconstructed, and the tectonic evolution was elucidated. The geostress distribution characteristics of the target coal seam (coal seam No. 11, P3l) in the study area were analyzed using the finite element numerical simulation method. The results indicate that the structural evolution of the Dahebian syncline in the study area can be divided into two stages. The Late Jurassic–Early Cretaceous stage (Early Yanshanian) is the first stage. Affected by the sinistral strike slip of the Weining–Ziyun–Luodian (WZL) fault zone, the derived stress field in the study area exhibits maximum principal stress (σ1) in the NEE–SWW direction. The Late Cretaceous stage (Late Yanshanian) is the second stage. Affected by the dextral strike slip of the WZL fault zone, the derived stress field exhibits σ1 in the NNW–SSE direction. The folds and faults formed in the first stage were modified by the structural deformation in the second stage. The dominant strikes of joints in the sedimentary strata are found to be in the NW–NNW (300°–360°) and NE (30°–60°) directions, with dip angles mostly ranging from 60° to 90°. The dominant strikes of coal microfractures are in the NW (285°–304°) and NE (43°–53°) directions. The distribution of geostress in the study area is characterized by high levels of geostress in the syncline center, decreasing towards the surrounding periphery. The overall trend of the geostress contour line is similar to the shape of the syncline and is influenced by folds and faults. The σ1 of coal seam No. 11 is vertical stress. The prediction results show that the joint density of coal seam No. 11 in the block is 36–50 joints/m, and the shape of the joint density contour line is also affected by the axial direction of the Dahebian syncline and the surrounding faults. The variation in coal seam joint density and the control effect of geostress on joints opening or closing affects the permeability of coal reservoirs. The study results provide significant guidance for the exploitation of CBM. [ABSTRACT FROM AUTHOR]

To investigate the controlling effect of tectonic stress field on coal and gas outburst, the gas geology, tectonophysics and rock mechanics methods were applied to analyze the influences of tectonic stress field on tectonic coal, in-situ stress and coal seam gas. Based on the case of coal and gas outburst, the effect of tectonic stress field on the distribution, type and strength of coal and gas outburst was studied. The mechanism and action forms of coal and gas outburst controlled by tectonic stress field were revealed. Results show that the tectonic stress field controls the characteristics of coal body structure distribution, coal body structure type and coal body strength. The compressive tectonic stress field is the main form of stress action for the tectonic coal formation, and the compresso-shear fault zone and interlayer-gliding fracture zone of fold form the development area of tectonic coal. The larger the tectonic stress field intensity is, the higher the fracturing degree of the coal body is, and the lower the coal body intensity is. The tectonic stress field controls the type, level and direction of the in-situ stress field. The region dominated by the intensive tectonic stress field belongs to the dynamic stress field and is at the high in-situ stress environment, and the direction of the tectonic stress field is the direction of the maximum horizontal principal stress of in-situ stress. The tectonic stress field affects the coal seam gas enrichment degree. Under the action of the strong tectonic stress field, the coal seam permeability is lower, the gas content and gas pressure are higher, and the compresso-shear structure zone forms the gas enrichment area. Under the action of the multistage tectonic stress filed, the distribution of tectonic coal, in-situ stress and gas of coal seam has the regional characteristic, which controls the partitioning and zonal distribution of coal and gas outburst. The horizontal compressional stress caused by the tectonic stress field controls the coal and gas outburst type dominated by coal and gas press-out. With the increase of the angle between the direction of the maximum horizontal principal stress and the axial direction of the roadway, the stress concentration factor increases and the coal and gas outburst intensity increases gradually. With the increase of maximum horizontal principal stress, the elastic deformation energy of coal and rock mass and gas expansion energy increase and the coal and gas outburst intensity increases. The research results provide a theoretical basis for predicting and preventing coal and gas outburst.

Tectonic stress fields are the key drivers of tectonic events and the evolution of regional structures. The tectonic stress field evolution of the Tanlu fault zone in Shandong Province, located in the east of the North China Craton (NCC), may have preserved records of the NCC's tectonic history. Borehole television survey and hydraulic fracturing were conducted to analyze the paleo and present tectonic stress fields. Three groups of tensile fractures were identified via borehole television, their azimuths being NNW–SSE, NW–SE and NE–SW, representing multiple stages of tectonic events. Hydraulic fracturing data indicates that the study region is experiencing NEE–SWW‐oriented compression and nearly‐N–S‐oriented extension, in accordance with strike‐slip and compression. Since the Cretaceous, the orientation of the extensional stress has evolved counterclockwise and sequentially from nearly‐NW–SE‐oriented to NE–SW‐oriented and even nearly N–S‐oriented, the stress state having transitioned from strike‐slip‐extension to strike‐slip‐compression, in association with the rotating and oblique subduction of the Pacific Plate beneath the NCC, with the participation of the Indian Plate. [ABSTRACT FROM AUTHOR]

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In January 2020, two moderate earthquakes with magnitudes of MS 5.4 and MS 6.4 occurred in the nappe structure of the boundary between the Southern Tianshan Mountains and Tarim Basin. To investigate the seismogenic structure of these two events, we systematically analyzed the earthquake sequence locations, focal mechanisms, and stress field in the source region. Using the P and S arrival-time data from January 1, 2009, to July 31, 2021, recorded by 18 seismic stations of the Xinjiang network, we obtained precise seismic event locations. Results show that the temporal and spatial distribution of the foreshock and aftershock sequences displays obvious differences in migration behaviors. The former is mainly distributed along the NNW direction, whereas the latter is distributed along the Ozgertau fault in the EW direction and characterized by a double-layer feature. Furthermore, we derived the focal mechanism solutions of the MS ≥ 4.0 events, including the MS 5.4 foreshock and the MS 6.4 main shock. The inversion results illustrate that the MS 5.4 foreshock is a strike-slip event, whereas the main shock and seven aftershocks are thrust events. Based on our results and the regional geological background, we conclude that the seismogenic structures of the MS 5.4 foreshock and MS 6.4 main shock are related to different faults. The MS 5.4 event is located in a blind "quasi-transformation" fault with the NNW direction, and the MS 6.4 earthquake occurs on a blind thrust nappe fault in the EW direction on the Kepingtage (Kalpintag) nappe. Our results indicate that the Tienshan orogenic belt has a complex tectonic environment. The difference in the strikes and dips of the MS 5.4 foreshock and MS 6.4 main shock reflects the stress compression in the near-NS direction in the source region. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Geodesy & Geodynamics (1671-5942) is the property of Editorial Board Journal of Geodesy & Geodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Natural fractures, like tectoclases, are essential in the formation of shale gas reservoirs and have been the focus of study for shale gas development. Tectoclases provide most storage space for gas and are largely controlled by the paleo-tectonic stress field in shale reservoirs of the Niutitang Formation, northern Guizhou area, China. An accurate prediction of the development and distribution of tectoclases in the reservoirs is of great significance to exploring and developing shale gas sweet spots in the area. Based on geological structure evolution and fracture characterization, this study is focused on factors that control the fracture development in the Niutitang Formation shale reservoirs in northern Guizhou through characterization and modeling of geomechanisms and tectonic movements. A geomechanical model is formulated for the shale reservoirs against the geological background of the area. On this basis, the fractures are predicted by using the acoustic emission data. Numerical simulation results show that the development and distribution of tectoclase is controlled by fault zones, some of which have no obvious turning points with tectoclase in the middle sections being more developed and fragmented than those at the two ends. Some of these have obvious S-shaped turning points where tectoclases are the most developed and fragmented.

On November 25, 2016, the MW 6. 6 earthquake occurred in Aketao, Xinjiang. It is shown that the rupture characteristics of the fault at the epicenter are closely related to the dynamics of the surrounding regional stress field. The precise characterization of the fault of the epicenter and the details of stress release in the regional crust can deepen understanding of the seismic dynamics around the epicenter, and also provide an important reference for determining the trend of local seismic activity in the future. Firstly, 26 after shock focal mechanisms near the epicenter were collected, and the stress field near the epicenter was obtained by using the grid search method. The results show that the principal compressive stress direction is 157. 36° with a dip angle of 1. 15° and the principal extensional stress direction is 66. 56° with a dip angle of 34. 98° in the area. This conclusion is consistent with the background that an dextral strike and thrust slip occurred on E-W azimuth fault by the intra-land subduction near the Pamir Plateau. Then by using 389 precisely located aftershocks and combination method of Gauss-Newton algorithm and simulated annealing algorithm, the seismogenic fault plane with a strike of 103. 64° and dip of 65. 65°is estimated, which basically overlap with the geometry of the right-lateral Muji fault. Then by projecting the estimated stress field onto the fault and the sliding angle of 152. 77°is obtained, which showing the dextral strike slip property of this earthquake. Finally, the relative stress distributions of variously shaped fault planes is retrieved by using the estimated regional stress tensor in this study. The results show that the relative shear stress on the fault plane of the earthquake is nearly 1, and therupture direction is nearly the same with the maximum shear stress direction in source region, which indicating that this earthquake occurred under the action of the stress field along the direction most favorable to release of the background stress. The findings of this study is important significance for in-depth understanding of the tectonic evolution and stress state in source region and its adjacent areas. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Geodesy & Geodynamics (1671-5942) is the property of Editorial Board Journal of Geodesy & Geodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We selected digital water level and corresponding air pressure data of 5 wells in the northeast Hainan，which are continuous，stable and with obvious solid tide since 2008. These wells are Haikou ZK26 well, Qionghai Jiaji well, Xiangrong village well, Volcanic fluid well, and Wenchang Tanniu well. We obtained porosity and volume compression coefficient between solid skeleton and water under undrained condition by the barometric efficiency and O1、M2 tidal factor smooth fitting. In horizontally layered one-dimensional aquifer mode，using partial aquifer parameters (porosity, water and solid skeleton volume compression coefficient) and relationship between water level variation and aquifer vertical stress，we quantitatively analyzed the dynamic change process of tectonic stress field of the northeast Hainan. Combined with the cumulative dynamic change of regional gravity field and the comprehensive analysis of regional tectonic activities based on GPS baseline, the results show that the northeast of Hainan is dominated by continuous stress weakening activities in recent years. In the future, it is necessary to track the occurrence of its turning changes and strengthen the close tracking of multi-disciplinary and multi means.

In addition to overall uplift of the Qiabuqia region during the Late Cenozoic, three deformation stages can be identified in the northeastern Qinghai–Tibet Plateau. Specifically, these deformation stages were recognized in areas east of the Gonghe Basin that surrounds Waliguan Mountain and include: 1) Late Miocene to Late Pliocene deformation—dominated by thrust napping with dextral strike-slipping; 2) Early Pleistocene to late middle period of Pleistocene deformation—fault structures were dominated by the dextral strike-slipping with thrust napping; and 3) end of Late Pleistocene to Middle Holocene deformation—thrust napping slowed down and finally braked, while the shallow surface began to loosen and extend at Qiabuqia region’s rear-edge. DR4 borehole drilling data indicate that the Xiangshuihe Formation’s buried depth is ∼1,000 m. The Xianshuihe Formation’s top section is characterized by normal fault–type (NF) tectonic stress, while the maximum principal tectonic stress (σ1) is perpendicular and the minimum principal tectonic stress (σ3) is horizontal. In contrast, the deep basement is characterized by thrust fault (TF) and strike-slip (SS) tectonic stress, while the σ1 is in the NE-SW direction, ranging from 20.1° to 75.3° with an average of 40.0°. Based on the aforementioned observations, it can be inferred that there are three sets of hidden faults in the basement of the Qiabuqia region: 1) the NW–NNW trending compressional–torsional faults; 2) the NE trending tensional–torsional faults; and 3) the NWW trending compressional–torsional faults. The findings in this study can potentially offer a robust geological basis for exploring and utilizing hot, dry rock resources within the Gonghe Basin.

Due to strong reservoir heterogeneity and low-resolution limit of geophysical data, it is difficult to predict fractures in ultra-deep reservoirs by conventional methods. In this research, we established a novel geomechanical model for prediction of fracture distribution in brittle reservoirs, especially for ultra-deep tight sandstone reservoirs. Methodologically, we intended to introduce the minimum energy dissipation principle considering time variable, combined with the generalized Hooke’s law containing damage variable, and obtained the energy dissipation rate expression corresponding to the energy dissipation process of brittle rocks. Combined with the three-shear energy yield criterion, the Lagrangian multiplier was introduced to deduce and construct the constitutive model and the failure criterion of rocks under the framework of the theory of minimum energy dissipation. Based on the law of conservation of energy, the stress-energy coupling characterization model of fracture density parameter was derived. Finally, all the improved geomechanical equations were incorporated into a finite element software to quantitatively simulate the distributions of tectonic stress filed and fractures based on paleo-structure restoration of Keshen anticline during the middle and late Himalayan periods. Its predictions agreed well with measured fracture density from reservoir cores and image logs.

The Qianyingzi Coal Mine is located in the west of the Suxian Mining District of the Huaibei Coalfield, eastern China. The study on structural development patterns and genetic mechanisms in this mine lays an important foundation for safe and efficiently underground mining, and is also the key to understanding the regional tectonic evolution. In this study, based on the analysis of three-dimensional seismic, drilling and underground measured data and regional tectonic correlation, the structures, evolution history and dynamic background of the Qianyingzi Coal Mine are discussed. The Carboniferous-Permian coal measure strata in the mine are generally a gentle syncline with a NNE-trending axis, and cut by a series of faults. The faults developed in this mine are mainly medium- and small-sized with a throw of less than 20 m, and the number of reverse faults is significantly greater than that of normal faults. The strikes of reverse and normal faults are both mainly NE, followed by NNE and nearly N‒S. According to the characteristics of structural geometry, tectonic association, fault property and cross-cutting relation, the structural deformation of coal measure strata in the Qianyingzi Coal Mine can be divided into five stages, and the corresponding tectonic stress fields are NWW‒SEE compressive stress, nearly E‒W compressive stress, NW‒SE compressive stress, nearly E‒W and NW‒SE extensional stresses, respectively. It developed the Fengjia Syncline with a NNE-trending axis in the first stage and nearly N‒S-striking reverse faults in the second stage, which were the results of foreland deformation and subsequent continent-continent collision during the convergence of the North China Craton and South China Plate in the Indosinian period. The NNE-striking reverse sinistral faults and NE-striking reverse faults developed in the third stage is related to the rapid oblique subduction of the Izanagi Plate toward the East Asian continental margin at the beginning of the Early Cretaceous in the western Pacific region. Later, the fourth and fifth stages of the nearly N‒S- and NE-SW-striking normal faults were developed under the backarc extensional background in eastern China during the Early Cretaceous. These new results can be used to guide the rational arrangement for underground mining and also provide a new understanding for regional tectonic evolution of the Huaibei Coalfield.

A strong earthquake with a magnitude Mw = 7.0 occurred on February 13, 2020, at a depth of 142 km in the vicinity of the Southern Kuril Islands. Over recent decades, there has been an anomaly near the focal zone in the earthquake distribution over the layers of the double seismic focal zone in accordance with the seismic dislocation kinematic type compared to the other areas of the intermediate depths of the southern part of the Kuril arc. Inversion of the earthquake focal mechanisms of intermediate depth was performed for the southern part of the Kuril Islands along the upper and lower layers of the seismic focal zone. In the upper layer, compression prevails along the slab; the axis of maximum compression σ3 is mainly parallel to the slab and is oriented at an angle of 140–160° (320–340°) to the direction of its dip, i.e., subparallel to the Pacific Plate motion vector in the mantle in this area. The stress state of extension along the slab prevails in the lower layer; the axis of minimum compression σ1 is parallel to the slab and is mainly rotated by 20° (200°) clockwise from the direction of its dip. This orientation of the principal stress axes could indicate that, in addition to the slab unbending, their formation is affected by the mantle resistance to its movement. In the upper and lower layers, we marked the areas where the shear stress prevails that correspond to the kinematic type of transform faults, which are presumably seismically active on the descending plate. The most complex pattern of the stress state of the medium was obtained near the focus of the earthquake that occurred on February 13, 2020. Here, in the upper layer, an area with the stress state of extension and orientation of the principal axes corresponds more to the lower layer. Seismic quiescence is observed in the lower layer, near the focus of this earthquake within the area 60 km wide along the island arc and at the entire interval of intermediate depths. [ABSTRACT FROM AUTHOR]

The study has been done on the orientation of the principal axes of tectonic stress field at intermediate depths of earthquakes of the southern flank of the Kuril-Kamchatka subduction system separately for the upper and lower double seismic focal zones. Use has been made of the NIED and GlobalCMT catalogue data. The computation-based results are presented on schemes of the stressed state of the investigated areas and in tables. In the context of the southern Kuril Islands, evidence has been provided for predominance of the maximum compressive stresses along the slab plane in the upper layer and minimal compressive stresses (deviation extension) in the lower layer. However, the principal axes of maximum and minimum compression are displaced in direction relative to the slab dip: by 30–40° counterclockwise for the compression axis in the upper layer, which coincides with the direction of plate movement, and clockwise for the extension axis in the lower layer. This might be caused by the right-lateral strike-slip component of the Pacific Plate subduction. Unlike the general trend, the orientation of the principal axes of the stress field beneath the central Hokkaido-related segments in the upper layer is almost identical to that in the lower layer. There have also been found the segments exposed to shear stress, with the most extensive located opposite the northern Kunashir Island and beneath the southern Hokkaido Island. The results obtained for major large groups of clusters show good accordance with those published by other authors. The discrepancies relate primarily to small groups of isolated clusters showing local stress field heterogeneities.

Shale reservoirs are well developed in Southeast Chongqing, of which the Longmaxi Formation is the main reservoir.Compared with other types of reservoirs, structural fractures are very well developed in this type of shale reservoirs, making this area potential for shale exploration.In this paper, based on the field survey data and typical regional geological sections, structural characteristics of the study area were analyzed.On this basis, a geological model for the shale reservoir was established.In order to restore the process of structural evolution within the study area of the Himalayan period, further, the finite element analysis software Ansys 15.0 are used.Simulation results fit the actual structural development well.Based on the results as well as Griffith fracture criterion and Coulomb-Moore fracture criterion, multiple influencing factors of shale reservoirs were comprehensively analyzed, and comprehensive fracture development coefficient IF were used to quantification of the fractures distribution prediction in shale reservoirs.The larger comprehensive fracture development coefficient IF is, the more developed the shale reservoir fractures would be.Therefore, shale reservoirs in the study area are classified into three categories: fracture favorable zone Type Ⅰ(IF ≥ 3.0, fracture very well developed), fracture favorable zone Type Ⅱ(3.0, 2.0], fracture good developed) and fracture favorable zone Type Ⅲ(2.0, 1.0].

The Huangshaping-Baoshan ore field is located in the Qianlishan-Qitianling ore concentration area in southern Hunan. The structure in the ore field is multi-period, and the ore body output is obviously controlled by the structure. In previous studies on the structure of this area, there is a lack of numerical simulation of the tectonic stress field for the process of tectonic deformation and its rock-controlling and ore-controlling processes. Therefore, based on the previous research results, this paper analyzes the typical geological structure points of the ore field in detail and further improves the stress state of the ore field structure system and the main tectonic period. Using ANSYS finite element numerical simulation software, this paper discusses the distribution characteristics and evolution of the tectonic stress field in the pre-mineralization stage and ore-forming stage of the ore field and summarizes the characteristics of tectonic deformation and the law of tectonic stress field controlling rock and ore control. It is considered that the near SN trending compression-torsional fracture is formed by regional SN compression before mineralization, and the KW-trending fracture shows obvious low strain energy, which provides favorable conditions for subsequent magmatic emplacement. The dominant position of the maximum principal stress in the ore-forming stage changed to the NE direction, and the maximum shear stress intensity was large, indicating that the deformation was strong in this period, and the pre-existing structure was strongly reformed. At this time, the KW-trending strain energy low-value fault zone was a powerful channel for magmatic emplacement and was limited by the NE-trending strain energy high-value fault zone in the periphery of the mining area, so that it could continuously gather and precipitate mineralization in the low strain energy area. Finally, through the comparative study of structural stress field characteristics of known ore points, it provides the basis for prospecting direction in this area. [ABSTRACT FROM AUTHOR]

We relocated 545 earthquakes that occurred in northern Jiangxi Province，from January 2008 to July 2019，using the double-difference location algorithm to improve relative location accuracy. Compared with the initial locations，the results of precise relocation in Jiujiang，Yichun and Xinyu areas are more concentrated. According to the precise relocation results，composite fault plane solution was calculated with the grid point test method. The result shows that the direction of maximum principal stress of Jiujiang and adjacent areas is nearly EW and that of the minimum principal stress is nearly NS，which is basically consistent with the previous research results. It is considered that the more research is needed to further refine and analyze characteristics of tectonic stress field in Jiujiang area. In Yichun and adjacent areas，the direction of maximum principal stress is nearly EW and that of the minimum principal stress is NNE and the area is in a thrust stress regime.

Shale is a low-porosity and low-permeability reservoir, and structural fractures are the main controlling factor for the migration and accumulation of shale gas. Moreover, tectonic fractures are controlled by the paleo-tectonic stress field. In this paper, taking the Longmaxi Formation of the Lintanchang area as an example, the finite element numerical simulation technology is used to analyze the distribution law of the paleo-tectonic stress field, and further, the fracture development areas under the superposition of two periods of tectonic stress are predicted using seismic, rock mechanics, and field data. The results show that the tectonic fractures developed in the Lintanchang area are mainly EW- and NNW-striking conjugate shear fractures formed in the Mid-Yanshanian period, followed by the NWW- and SWW-striking conjugate shear fractures formed in the late Yanshanian period. The distribution of tectonic fractures is affected by faults, folds, rock physical parameters and tectonic stresses. It is found that the comprehensive fracture coefficients of the anticline core and fault areas are both greater than 1.1, which are the areas with the most developed structural fractures, and these areas have poor shale gas preservation conditions. However, the comprehensive fracture coefficients of the western flanks of the anticline and the eastern and western dipping ends are between 1.0 and 1.1, which are areas with better shale gas preservation conditions. In addition, the development degree of tectonic fractures in the east and northwest areas of the Lintanchang anticline is lower than that in other areas. The comprehensive fracture coefficients of shale in these areas are between 0.9 and 1.0. The shale is in a state of “breaking without cracking”, and shale gas can be well preserved.

Copyright of Journal of Geodesy & Geodynamics (1671-5942) is the property of Editorial Board Journal of Geodesy & Geodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Earthquake focal mechanisms in the Southern Kuril-Kamchatka and Northern Japan subduction zones were analysed to investigate the features of the tectonic stress field inside the Pacific lithospheric plate subducting into the upper mantle. Earthquake focal mechanism (hypocenter depths of more than 200 km) were taken from the 1966– 2018 NIED, IMGiG FEB RAS and GlobalCMT catalogues. The tectonic stress field was reconstructed by the cataclastic analysis method, using a coordinate system related to the subducting plate. In most parts of the studied seismic focal zone, the axis of the principal compression stress approximately coincides with the direction of the Pacific lithospheric plate subduction beneath the Sea of Okhotsk. It slightly deviates towards the hinge zone separating the studied regions. The principal tension stress axis is most often perpendicular to the plate movement, but less stable in direction. This leads to compression relative to the slab in some parts of the studied regions, and causes shearing in others. The hinge zone is marked by the unstable position of the tension axis and high values of the Lode–Nadai coefficient, corresponding to the conditions of uniaxial compression, while the compression direction remains the same, towards the slab movement. Two more areas of uniaxial compression are located below the Sea of Japan at depths of 400–500 km.

The Kexueshan Basin in the western Ordos Block is characteristic of typical regional superimposed folds in the Jurassic strata, documenting the main tectonic shortening since the Mesozoic. Field structural investigation, fault kinematic analysis, together with regional structural analysis, we reconstruct two-phase tectonic stress fields related to crustal shortening. Synthesizing the regional structural analysis and geochronology, two stages of tectonic evolution are proposed in the Kexueshan Basin since the late Mesozoic. In the mid-late Middle Jurassic (J2), controlled by NW-SE compaction, NW-SE structures formed in the Kexueshan Basin on the western margin of the Ordos Block, marked by NE-to NNE-trending folds and thrust faults. Growth strata found in the study area constrain the starting time of the NW-SE structures. This shortening is likely related to a combination of the southward convergence of the Siberian plate and the northwestward subduction of the Pacific plate. In the end Cenozoic (N12-N2), the tectonic stress field was transformed to NE-SW compression, resulting in the development of NW- to NNW-trending fold structures, which were superimposed on early NE-to NNE-trending structures to produce regional superimposed folds. The tectonic shortening coincided with the northeastward growth of the Tibetan Plateau.

Regional tectonic stress fields are key crustal stress elements that drive tectonic movements and are associated with regional tectonics and geological resources. Regional tectonic stress field evolution of the Jinzhou area, located in the eastern block of the North China Craton (NCC), may provide a deeper understanding of tectonics of western Liaoning and the NCC. This work conducted borehole television, hydraulic fracturing and focal mechanism solutions to invert the paleo and present regional tectonic stress fields. Four groups of tensile fracture in the southern Jinzhou area were identified via borehole television, and their azimuths were NNW–SSE, NWW–SEE, nearly W–E and NE–SW in temporal order representing four stages of extensional tectonic events. Hydraulic fracturing and focal mechanism solutions showed that the stress status was normal fault and strike-slip, revealing that the southern Jinzhou area is undergoing NEE–SWW-oriented compression and nearly N–S-oriented extension in accordance with the strike-slip mechanism. From the Early Cretaceous to the present, the direction of the regional extensional stress in the southern Jinzhou area has evolved counterclockwise and sequentially from NNW–SSE to NWW–SEE, W–E, NE–SW and nearly N–S, and the regional tectonic mechanism has transited from extension to extension-strike-slip to strike-slip, leading to the current tectonic framework. [ABSTRACT FROM AUTHOR]

China is located in the southeast of the Eurasian Plate and is subject to the effects of subducting, squeezing and collision by the Pacific Plate, Philippine Plate and Indian Ocean Plate. It has exceptional geotectonic structure. Based on the satellite gravity data with high precision, high resolution and ample geophysical information, combined with geological data, by using satellite gravity potential field and its full tensor gradient, this paper studies the distribution characteristics of gravity anomalies and the identification of tectonic boundaries in East Asia. Results suggest that the Bouguer gravity anomaly in eastern China reduces gradually from east to west, mostly in the direction of NNE; in the western, it reduces gradually in a wave mode from north to south, mainly in the directions of NW and NWW. In general, the stress field reduces gradually from west to east, and the tectonic of stress field in western China is complex. The change in eastern China is relatively simple. In addition to the above study results, we update the extension route of Red River fault zone and deduce the tectonic unit boundary between the North China and South China active tectonic block regions. This paper identifies in East Asia 6 primary active tectonic blocks, 22 secondary active tectonic blocks, 7 tertiary active tectonic blocks, and the 20 active tectonic block boundary zones. The results of this study can improve the understanding of gravity anomalies and boundary structures in China and surrounding regions, and provide certain geophysical supports for geological structure analysis and crustal dynamic process. [ABSTRACT FROM AUTHOR]

Structural fractures in carbonate reservoirs contribute prominently to hydrocarbon migration and accumulation. In this paper, the accuracy of structural fracture prediction is improved by two aspects of numerical simulation of traditional tectonic stress field and fracture distribution prediction methods in carbonate reservoirs. (1) The grid generation of finite element models for geological models is prioritized. Next, uniaxial and triaxial compression tests, well logging data, and 3D seismic data volume inversion are used to create a 3D volume of heterogeneous rock mechanics data that accurately reflects the geological body. Then, using the data, attribute assignments are made in the finite element model to create the three-dimensional heterogeneous rock mechanics model. This enhancement significantly diminishes the error induced by attributing rock mechanics parameters to individuals. (2) The size and orientation of in-situ stress are measured using acoustic emission, paleomagnetic, and wave velocity anisotropy tests in combination with imaging logging data. By introducing an adaptive boundary condition method to precisely calculate the in-situ stress magnitude at the applied boundary, we simulate the paleo- and current tectonic stress fields within the study area. The fracture rates for tension and shearing are calculated using the Griffith and Coulomb-Mohr fracture criteria. Based on the statistical results of characteristic fracture parameters at the core and imaging logging scales in the study area, the proportion of tensile and shear fractures is determined, and then the comprehensive fracture coefficient of carbonate reservoirs is calculated. A model for quantitatively predicting the multiperiod linear density of fractures suitable for carbonate reservoirs is developed following a thorough analysis of the various effects of multiperiod tectonic stress on the formation and alteration of reservoir fractures. The utilization of this technique in quantitatively forecasting the linear density of multiperiod fractures in carbonate reservoirs in the Tahe Oilfield, Tarim Basin, exhibits favorable feasibility. This paper improves the traditional method of tectonic stress field simulation and innovatively proposes a new method of high-precision numerical simulation of tectonic stress field based on heterogeneous rock mechanics model and adaptive boundary condition optimization. A quantitative prediction model for multi-period fracture linear density in carbonate reservoirs was developed. [Display omitted] • Constructed a high-precision heterogeneous rock mechanics model. • Adaptive boundary conditions improve the accuracy of numerical simulation. • Reconstructed the tectonic stress field of the three periods. • Achieved superimposed prediction of three-period fracture line density. • A prediction model for multi-period fracture line density was constructed. [ABSTRACT FROM AUTHOR]

An understanding of the tectonic stress field distribution in the carbonate reservoirs of the Tahe Oilfield is essential for oil and gas migration and reservoir reconstruction. This study adopts a geological genesis perspective and integrates the unique attributes of the carbonate reservoirs in the Tahe Oilfield to simulate three-dimensional stress fields using the finite element method and Petrel software. The simulation, which takes pore pressure and boundary constraints into consideration, aligns with the findings of acoustic emission tests conducted by previous researchers and validates the model by corroborating the maximum horizontal principal stress direction with imaging logging interpretations. With subsequent utilization of the generalized Coulomb-Mohr shear failure criterion and the Griffith generalized maximum tensile stress criterion, the simulated stress enables the prediction of the total fracture intensity. To complement this analysis, we integrate seismic data and fault formation mechanisms to characterize variations in fracture intensity within distinct regions of the study area. Three key findings emerge from this investigation. First, due to the Hercynian thermal event, X-shaped conjugate faults display a disproportionately high degree of development compared to other primary fractures. Analyzing the mechanisms of formation and development of these X-shaped strike-slip faults reveals discernible differences in deformation characteristics between NW-trending and NE-trending faults, with the former exhibiting a greater propensity for fracture rupture and efficient oil-gas migration. Second, fault intersections are critical and efficient conduits for fluid accumulation and thereby contribute to reservoir formation. Lastly, exclusive of X-shaped conjugate faults, NE-trending faults exhibit the greatest propensity for oil and gas accumulation and migration. Collectively, these findings facilitate the identification of areas favorable for oil and gas migration and provide a crucial mechanical analysis that can inform the exploration and development of the Tahe Oilfield. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The tectonic stress field is one of the important factors to control the enrichment and high yield of coalbed methane, and it has a very important application in many links of coalbed methane exploration and development. Based on the investigation and analysis of the widely developed conjugate joints in the Mesozoic and Cenozoic strata in Baode block and its surrounding areas, this paper reconstructed the Mesozoic and Cenozoic tectonic stress field by using the method of tectonic geology. The analysis and investigation show that there are three major tectonic stress fields in the Mesozoic and Cenozoic in the area, and it is considered that the current in-situ stress direction is NE-SW. At the same time, the maximum and minimum horizontal principal stress of the main coal seam (No. 8+9 coal) are calculated by using the DST data of CBM Wells in the area, and the relationship between in-situ stress and permeability of coal seam is discussed. Based on the geostress data obtained, it is considered that NE-SW direction artificial fracture will occur in the fracturing process of the main coal seam in Baode block, and the pressure fracture is a vertical fracture extending along the direction of the maximum horizontal principal stress, and the well hole is relatively stable. On this basis, the optimal plan of CBM development well pattern is put forward, one is that the long diagonal of rhombus is parallel to the direction of the maximum horizontal principal stress, the other is that the long diagonal of rhombus is parallel to the direction of the dominant fracture. [ABSTRACT FROM AUTHOR]

The study of the construction of a micro-scale rupture parameter from the perspective of rock stress and strain is a frontier in geoscience. The strain energy density (U) can quantitatively characterize the probability of internal micro-scale ruptures in different types of rock. Based on this, in this paper, a systematic forecasting method for tight sandstone sweet spots in a low-amplitude tectonic zone based on U -value calculations was proposed. The specific steps are as follows. First, a geological model of the target layer was created, and a new rock mechanics parameter assignment method based on sedimentary facies control principle was proposed. Then, the palaeo-tectonic stress field of the target layer in the Yanshanian period was recovered through the boundary loading. Finally, the strain energy density distribution of the target layer was obtained based on energy conservation principle. The simulation results of the paleo-tectonic stress field show that, the distribution of horizontal stress is mainly affected by lithology and local structure, and the vertical stress is mainly affected by the burial depth. Stress diffusion occurs in some areas, which are mainly affected by lithologic mutations or complex structures. The U values of the target layers have a band-like distribution and are mainly distributed between 0.12 and 0.30 J·m-3. The relationship between strain energy density and productivity of tight sandstone reservoirs was analyzed, and the criteria for distinguishing sweet spot areas based on U values were proposed. This method is applicable to strongly heterogeneous tight sandstone reservoirs in the low-amplitude tectonic zone of the Ordos Basin and have reference values for similar types of reservoirs around the world.

A modern tectonic stress field for the north‐eastern margin of Tibetan Plateau was determined using linear inversion. Focal mechanism solutions and the depths of 54 earthquakes from 2009 to 2017 were obtained from broadband seismic waveforms. We derived the tectonic stress field using the SATSI (Spatial and Temporal Stress Inversion) software based on the damped linear inversion method. The stress tensor structures are primarily indicative of strike‐slip and thrust faulting; their distributions are controlled by the West Qinling and Haiyuan faults. The Longxi Block is surrounded by two faults dominated by thrust faulting; the regions in the periphery of the faults, (e.g., West Qingling Fault Zone and Liupanshan Basin) are primarily characterized by strike‐slip faulting. However, normal faulting has developed in the Haiyuan–Zhongwei Belt of Liupanshan Basin, indicating that the latest tectonic regime is an NNW–SSE extension instead of a strike‐slip fault with a thrust component, as has been previously suggested. This anomalous stress mechanism reflects the combined effects of block rotation and local extension resulting from movement along strike‐slip faults. The West Qinling Fault is dominated by thrust faulting instead of strike‐slip faulting. The Haiyuan–Liupanshan and Niushoushan–Luoshan faults are predominantly strike‐slip faulting. The directions of the maximum stress axes (σ1) in both Liupanshan Basin and the Longxi Block are ENE–WSW down to Liupanshan in the south and West Qinling Fault Zone, where the stress axes gradually rotate clockwise to E–W. The modern tectonic stress field implies that regional stress originates from far‐field effects of Indian and Eurasian plate collision. [ABSTRACT FROM AUTHOR]

The geological interpretation of the velocity model for the DOBRE-5 deep seismic sounding profile, which runs across Fore-Dobrogea, the northwestern shelf of the Black Sea, and the Crimean Peninsula, resulted in the recognition of several major fault zones. The first zone consists of a system of closely spaced listric normal faults that gently dip S–SE and are interpreted as the structural expression of the suture between the East European Platform and Crimean segment of the Scythian Plate. The second and third zones, which were established for the first time, are thrust-type structures—the Upper and Lower Central Crimean thrusts. The admissible variants of the attitudes of these faults were analyzed and the kinematic settings of their formation were reconstructed by tectonophysical analysis on stereographic nets. It was demonstrated that the inception and subsequent activation events of the junction zone of platforms of different age and the Central Crimean thrust fault system took place in alternating (inverse) kinematic settings of ~N–S longitudinal compression and crustal extension. The chronological order of changes of the kinematic settings and periods, in which a certain setting was predominant, is governed by crustal oscillation cyclicity, expressed in the composition and areal extent of the platform sequences of the Crimean Plain and northern Black Sea coast. The crustal oscillation cyclicity, based on a comparison with paleogeodynamic reconstructions of the Mediterranean Belt, is governed by trends in the evolution of back-arc basins of Neo-Tethys extending along the southern margin of Eurasia in front of subduction zones that existed during the initial periods of the Alpine stage at various distances from the study area. [ABSTRACT FROM AUTHOR]

Here, we show the present-day tectonic stress field and regional GPS velocity and strain rate fields in Hubei Province, central China. Our results are calculated based on the digital observation data from 01 January 2010, to 31 December 2017, by using the seis-CAP, P-wave first motion, and grid search methods and the software GAMIT/GLOBK10.4. The results show that the P axis azimuths of focal mechanism solutions, the principal compressional stress field, and the regional velocity and strain rate fields are conformably compressional in a NW–SE direction. The regional stress shape ratio R values are relatively low, and the faults are dominantly compressive-shear or compresso-shear faults. The average velocity modulus value for the GPS observation stations in western Hubei is 6.1 mm/a, which is higher than that in eastern Hubei (5.4 mm/a). The average velocity modulus value in the Jianghan Basin interior is relatively low (4.4 mm/a), while that in the northwestern Jianghan Basin is higher (7.6 mm/a). The strain rate field is characterized by NW–SE compression accompanied by NE–SW tension. The results suggest that the present-day crustal movement in Hubei Province is mainly controlled by collisions with the Indian Plate in the west and the Philippine Plate in the east and the consequent crustal shortening induced by western Hubei wedging into the Jianghan Basin. Further, the resistance by the thrust-and-fold belt in eastern Hubei contributes to the principal compressional movement in the study area. The T axis azimuth of focal mechanism solutions is consistent with the principal extensional stress field direction. In the central and northern Jianghan Basin, the R values are relatively high, the faults are mainly transtensional, and the crustal deformation is mainly extensional, which may be affected by the denudation, thinning and rapid rebound of the Dabie Orogen, resulting in tectonic extrusion and flow in the Jianghan Basin to both the NE and SW sides. [ABSTRACT FROM AUTHOR]

Focal depths of the 2008 MS6.1 Panzhihua earthquake sequence and tectonic stress field in the source area are investigated. Source depths of 24 earthquakes in Panzhihua earthquake sequence with a magnitude M≥3.0 were determined using the seismic depth phase sPL; additionally, the focal depths of 232 earthquakes were measured by fitting the three-component waveforms of the P and S waves. The source depth of the main shock is ~12 km. The majority of the aftershocks with magnitude M≥3.0 occurred in the brittle upper crust at the depths range of 12–18 km. Further, the Source mechanisms of the 232 events around the Panzhihua earthquake source area were determined, and the results show that the earthquakes have predominantly strike-slip mechanisms in the Dianzhong Block, but display complexity of the focal mechanisms outside and near the boundary of the Dianzhong block. The 232 earthquake mechanisms from this study are combined with the solutions from the Global Centroid Moment Tensor (GCMT) catalog to derive 2D stress field. The inversion results show that the Dianzhong block is predominantly under a strike slip faulting regime and the direction of the maximum principal compression σ1 is northwest-southeast (NW-SE)-trending. The distribution is coincide with GPS velocity field. However, orientations of principal stress axes as well as the faulting types change outside and near the Dianzhong block. The results show that the tectonic stress field in the study area is predominantly controlled by the southeast (SE)-trending horizontal movement and clockwise rotation of the Dianzhong block as a result of the eastward movement of eastern Tibetan meeting the old and rigid South China block (SCB). The Panzhihua earthquake ruptured at ~12 km depth where the tectonic stress regime is under the SE-direction horizontal compression and the NE-direction horizontal extension. [ABSTRACT FROM AUTHOR]

The reliability of inversion of initial horizontal tectonic stress field of deep rock mass is very important for the subsequent calculation results of engineering. In order to study the 3DEC simulation inversion method of the initial tectonic stress field of the rock mass in the deep mining area, the displacement boundary condition and the inversion method based on the initial strain energy theory were compared and analyzed. Results indicated that the displacement boundary condition can only simulate the initial self weight stress field, and the inversion method based on the initial strain energy theory can better invert the initial horizontal tectonic stress field of the deep rock mass. The application of this method to the inversion analysis of the ground stress field of the section line 40 in the Shizishan mining area, which indicated that the maximum horizontal principal stress trace of each point in the deep was horizontally distributed, and the contour interval was good. The research results are of great significance to use 3DEC to generate the initial ground stress field of high tectonic stress type mine and to simulate its mining. [ABSTRACT FROM AUTHOR]