A study on abnormal temperature variation of the earthquake in Jiujiang, China （2005） according＇to additive tectonics stress

A variation model of additive tectonics stress caused by celestial tide-generating force is put forward to explain its relationship with seismic fault sliding. Based on the model, the temperature data from National Center for Environmental Prediction （NCEP） before and after the earthquake in Jiujiang （China） on Nov.26, 2005 are studied. The figure of the temperature variation describes the effect of celestial tide-generating force on fault plane. The variation＇of temperature is not only associated with the seismic deformation but also in step with the evolution of fi＇iction of rock under the stress. The abnormal change of temperature can be used in the studies of short- impending earthquakes.

Tensile Fractures and in situ Stress Measurement Data Constraints on Cretaceous-Present Tectonic Stress Field Evolution of the Tanlu Fault Zone in Shandong Province,North China Craton

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-Soriented 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.

Advances in experiments and numerical simulations on the effects of stress perturbations on fault slip

Laboratory experiments and numerical simulations on rock friction perturbations,an important means for understanding the mechanism and influencing factors of stress-triggered earthquakes,are of great significance for studying earthquake mechanisms and earthquake hazard analysis.We reviews the experiments and numerical simulations on the effects of stress perturbations on fault slip,and the results show that stress perturbations can change fault stress and trigger earthquakes.The Coulomb failure criterion can shed light on some questions about stress-triggering earthquakes but cannot explain the time dependence of earthquake triggering nor be used to investigate the effect of heterogeneous stress perturbations.The amplitude and period are important factors affecting the correlation between stress perturbation and fault instability.The effect of the perturbation period on fault instability is still controversial,and the effect of the high-frequency perturbation on earthquakes may be underestimated.Normal and shear stress perturbation can trigger fault instability,but their effects on fault slip differ.It is necessary to distinguish whether the stress perturbation is dominated by shear or normal stress change when it triggers fault instability.Fault tectonic stress plays a decisive effect on the mode of fault instability and earthquake magnitude.Acoustic emission activity can reflect the changes in fault stress and the progression of fault nucleation,and identify the meta-instability stage and precursor of fault instability,providing a reference for earthquake prediction.

Geostress measurements near fault areas using borehole stress-relief method

To minimize negative effects of geostress distribution on mining safety near the fault areas, the UPM40 triaxial geostress testing system was introduced to conduct in-situ geostress measurements at three sites and nine points by the borehole stress-relief method. The results of strain?confining pressure curves show that rock masses at the three measuring sites exhibit comprehensive linear elasticity in spite of various fissures or cracks within rocks. Horizontal and vertical stress components distribute discrepantly near the fault areas, and the maximum lateral pressure coefficient is as high as 6.15. The maximum principle stress ranges from 8.01 to 14.93 MPa, and stress directions are in the range of N78.07°W?N17.55°W. Geostresses near fault areas are dominated by the horizontal tectonic stresses, while the lower values, compared to those under similar geological conditions are due to stress release by the fault. Additionally, the fault and shear stress nearby are partially responsible for asymmetric elongation and southwesterly migration of orebodies.

Active Faulting Pattern,Present-day Tectonic Stress Field and Block Kinematics in the East Tibetan Plateau

This paper examines major active faults and the present-day tectonic stress field in the East Tibetan Plateau by integrating available data from published literature and proposes a block kinematics model of the region. It shows that the East Tibetan Plateau is dominated by strike-slip and reverse faulting stress regimes and that the maximum horizontal stress is roughly consistent with the contemporary velocity field, except for the west Qinling range where it parallels the striking of the major strike-slip faults. Active tectonics in the East Tibetan Plateau is characterized by three faulting systems. The left-slip Kunlun-Qinling faulting system combines the east Kunlun fault zone, sinistral oblique reverse faults along the Minshan range and two major NEE-striking faults cutting the west Qinling range, which accommodates eastward motion, at 10--14 mm/a, of the Chuan-Qing block. The left-slip Xianshuihe faulting system accommodated clockwise rotation of the Chuan-Dian block. The Longmenshan thrust faulting system forms the eastern margin of the East Tibetan Plateau and has been propagated to the SW of the Sichuan basin. Crustal shortening across the Longmenshan range seems low （2-4 mm/a） and absorbed only a small part of the eastward motion of the Chuan-Qing block. Most of this eastward motion has been transmitted to South China, which is moving SEE-ward at 7-9 mm/a. It is suggested from geophysical data interpretation that the crust and lithosphere of the East Tibetan Plateau is considerably thickened and theologically layered. The upper crust seems to be decoupled from the lower crust through a decollement zone at a depth of 15-20 kin, which involved the Longmenshan fault belt and propagated eastward to the SW of the Sichuan basin. The Wenchuan earthquake was just formed at the bifurcated point of this decollement system. A rheological boundary should exist beneath the Longmenshan fault belt where the lower crust of the East Tibetan Plateau and the lithospheric mantle of the Yangze block are juxtaposed.

Contemporary tectonic stress field in China

The contemporary tectonic stress field in China is obtained on the basis of Chinese stress field database and Harvard CMT catalogue. Result of the inverted tectonic stresses shows that the maximum principal stress axis strikes nearly north-south direction in the west part of Tibet plateau, ENE direction in North China. In Central China, its strikes show a ra- diated pattern, i.e., NNE in north part and NNW in south part. The detailed stress field parameters of nearly whole China are given and can be used in geodynamic stress field simulation and earthquake prediction.

The Relationship between Fractures and Tectonic Stress Field in the Extra Low-Permeability Sandstone Reservoir at the South of Western Sichuan Depression

The formation and distribution of fractures are controlled by paleotectonic stress field, and their preservative status and effects on development are dominated by the modern stress field. Since Triassic, it has experienced four tectonic movements and developed four sets of tectonic fractures in the extra low-permeability sandstone reservoir at the south of western Sichuan depression. The strikes of fractures are in the S-N, NE-SW, E-W, and NW-SE directions respectively. At the end of Triassic, under the horizontal compression tectonic stress field, for which the maximum principal stress direction was NW.SE, the fractures were well developed near the S-N faults and at the end of NE-SW faults, because of their stress concentration. At the end of Cretaceous, in the horizontal compression stress fields of the NE-SW direction, the stress was obviously lower near the NE-SW faults, thus, fractures mainly developed near the S-N faults. At the end of Neogene-Early Pleistocene, under the horizontal compression tectonic stress fields of E-W direction, stress concentrated near the NE-SW faults and fractures developed at these places, especially at the end of the NE-SE faults, the cross positions of NE-SW, and S-N faults. Therefore, fractures developed mostly near S-N faults and NE-SW faults. At the cross positions of the above two sets of faults, the degree of development of the fractures was the highest. Under the modern stress field of the NW-SE direction, the NW-SE fractures were mainly the seepage ones with tensional state, the best connectivity, the widest aperture, the highest permeability, and the minimum opening pressure.

Three dimensional tectonic stress field in North China

According to the latest data of geological structure, geophysics, in-situ stress measurement and focal mechanism,3-D tectonic stress field model in North China is built and 3-D tectonic stress field pattern of North China aresimulated by finite element method. Then the overall characteristics and regional specific feature of North Chinaare studied. Finally, the influences of the valid dynamic boundary conditions of North China Block, active faultsand the inhomogeneity of crustal medium on tectonic stress field of North China are investigated.

End Late Paleozoic tectonic stress field in the southern edge of Junggar Basin

This paper presents the end Late Paleozoic tectonic stress field in the southern edge of Junggar Basin by interpreting stress-response structures （dykes, folds, faults with slickenside and conjugate joints）. The direction of the maximum principal stress axes is interpreted to be NW-SE （about 325°）, and the accommodated motion among plates is assigned as the driving force of this tectonic stress field. The average value of the stress index Rt is about 2.09, which indicates a variation from strike-slip to compressive tectonic stress regime in the study area during the end Late Paleozoic period. The reconstruction of the tectonic field in the southern edge of Junggar Basin provides insights into the tectonic deformation processes around the southern Junggar Basin and contributes to the further understanding of basin evolution and tectonic settings during the culmination of the Paleo- zoic.

Evolution characteristics of Quaternary tectonic stress field in the north and east margin of Qinghai-Xizang plateau

By inversion of fault slip data for Quaternary tectonic stress field and the analysis of crustal deformation after lateTeriary. we explaincd the evolution of crustal dynamic about the north and east margin of Qinghai-Xizang (Tibet)plateau since Miocenc. From middle or late Miocene to early Pleistocene, the tectonic stress field was featured by amaximum principal compression which was coming from the collision of india Plate continued to the boundaryof the plateau. and was basically of reverse faulting type. Since the late period of early Pleistocene, Pleistocene continuedto push northward and the compressional deformation of the plateau interior increased continuously, meanwhile,N W-SE extension appeared on the east side of the plateau. This formed a favorable condition for the interior block offoe plateau to slide towards east and southeast, causing the faults surrounding the plateau to change from thrust tostrike-slip. -The contemporary tectonic stress field was formed from the late period of early Pleistocene and continuedto present. The direction of maximum principal compressional stress rotated clockwise with respect to the previoustectonic stress held. the stress field was mainly of strike-slip type.

Similarity simulation of bolt support in a coal roadway in a tectonic stress field

In order to study the mechanism of bolt support and the behavior of strata in a coal roadway under tectonic stress,deformation and destruction of a roof,floor and sides were studied using an experiment in similarity simulation.We also studied the mechanism and types of bolt support functions in the coal roadway.The results show that with an increase in horizontal tectonic stress,the strata in the roof and floor of the roadway gradually separate and become shear failure areas.Coal in side walls moves,but its integrity remains intact.Side bolts are mainly affected by tension and roof bolts by the effect of shear.

Study on relation between tectonic stress and coal-mining subsidence with similar material simulation

Using a minitype and stress-type test device for similar material simulation of coal-mining subsidence, the relation between tectonic stress and coal-mining subsidence was successfully simulated, furthermore, the test period of similar material simulation was obviously shortened and the test process was more dexterous and convenient. To do simi-lar material simulation with the minitype and stress-type test device was feasible and high-efficient. Bringing two models with the same geological and mining conditions to bear lateral compressive stress and tensile stress respectively and simulating the process of underground mining, the test results indicate that: under the compressive stress, the col-lapse of the coal roof occurs belatedly and the damaged range in cover of coal seam is smaller, therefore the movement and deformation of the cover and its damage to the ground geological environment are not evident; whereas under tensile stress, the situation is contrary to which mentioned above. A conclusion was obtained from the test that the ground environment hazards in coal mining areas were controlled by the regional geo-logical tectonic stress field.

The seismicity and tectonic stress field characteristics of the Longmenshan fault zone before the Wenchuan M_S8.0 earthquake

The seismicity of Longrnenshan fault zone and its vicinities before the 12 May 2008 Wenchuan Ms8.0 earthquake is studied. Based on the digital seismic waveform data observed from regional seismic networks and mobile stations, the focal mechanism solutions are determined. Our analysis results show that the seismicities of Longmenshan fault zone before the 12 May 2008 Wenchuan earthquake were in stable state. No obvious phenomena of seismic activity intensifying appeared. According to focal mechanism solutions of some small earthquakes before the 12 May 2008 Wenchuan earthquake, the direction of principal compressive stress P-axis is WNW-ESE. The two hypocenter fault planes are NE-striking and NW-striking. The plane of NE direction is among N50°-70°E, the dip angles of fault planes are 60°-70° and it is very steep. The faultings of most earthquakes are dominantly characterized by dip-slip reverse and small part of faultings present strike-slip. The azimuths of principal compressive stress, the strikes of source fault planes and the dislocation types calculated from some small earthquakes before the 12 May 2008 Wenchuan earthquake are in accordance with that of the main shock. The average stress field of micro-rupture along the Longmenshan fault zone before the great earthquake is also consistent with that calculated from main shock. Zipingpu dam is located in the east side 20 km from the initial rupture area of the 12 May 2008 Wenchuan earthquake. The activity increment of small earthquakes in the Zipingpu dam is in the period of water discharging. The source parameter results of the small earthquakes which occurred near the initial rupture area of the 12 May 2008 Wenchuan earthquake indicate that the focal depths are 5 to 14 km and the source parameters are identical with that of earthquake.

Rules of distribution in a plastic zone of rocks surrounding a roadway affected by tectonic stress

In order to study the rules of distribution in a plastic zone of rocks, surrounding a roadway, affected by tectonic stress, we first analyzed the mechanics of a roadway affected by tectonic stress and derived a theoretical formula for the plastic zone of rocks surrounding a roadway. We also analyzed the distribution characteristics of the plastic zone under different levels of tectonic stress, vertical pressure, cohesion and friction angle of the surrounding rock. Secondly, we used numerical simulation to analyze the range and shape features of the plastic zone of rocks surrounding the roadway, given different tectonic stress levels. Finally we used a rock drilling detector to carry out field measurements on the broken state of rock surrounding the roadway at the –700 substation and channels in the Xinzhuang mine of the Shenhuo mining area. Given the measured ground stress, we analyzed the relationship between tectonic stress and the distribution of this plastic zone. Our results show that the range of the plastic zone at the top and bottom of the roadway increases with an increase in tectonic stress and this increase is especially obvious at the roadway corner.

Modern tectonic stress field in Southwest Yunnan, China

By means of inversion of fault slip data, the parameters of 20 tectonic stress tensors in Southwest Yunnan region are determined. Compared with the average stress field of the region obtained from focal mechanism solutions, the following characteristics of modern tectonic stress field in this region are obtained. From the west of Zhenyuan-Yingpanshan fault to the south of Longling fault zone, the maximum compressional stress is in NNE direction and the stress regime is mainly of strike-slip type. In Longling fault zone and the area north to it, the direction of maximum compressional stress is near-NS or NNW, the stress regime is of strike-slip type.

Determination of the direction and magnitude of recent tectonic stress in the Xianshuihe fault zone using fault slip data

In this article,a method to determine the complete stress tensor by use of fault slip data in combination with experimental parameters of rock mechanics is elucidated;the direction and magnitude of recent tectonic stress in the Xianshuihe fault zone are determined by this method from a great deal of active fault striae data observed in the fault zone and the envelope of rock fracture determined experimentally for rock samples collected from the fault zone;and the applicability of the method and reliability of calculation results are discussed.

An Estimation Method of Stress in Soft Rock Based on In-situ Measured Stress in Hard Rock

The law of variation of deep rock stress in gravitational and tectonic stress fields is analyzed based on the Hoek-Brown strength criterion. In the gravitational stress field,the rocks in the shallow area are in an elastic state and the deep,relatively soft rock may be in a plastic state. However,in the tectonic stress field,the relatively soft rock in the shallow area is in a plastic state and the deep rock in an elastic state. A method is proposed to estimate stress values in coal and soft rock based on in-situ measurements of hard rock. Our estimation method relates to the type of stress field and stress state. The equations of rock stress in various stress states are presented for the elastic,plastic and critical states. The critical state is a special stress state,which indicates the conversion of the elastic to the plastic state in the gravitational stress field and the conversion of the plastic to the elastic state in the tectonic stress field. Two cases stud-ies show that the estimation method is feasible.

Modern tectonic stress field deeply in Xuzhou Coal Mine

By inverting fault slip data, the parameters of 12 tectonic stress tensors in the mine region can be determined. The following characteristics can be obtained for recent tectonic stress fields, which are found deep in the study region. The results show that the recent tectonic stress field mainly presents the characteristics of near NWW-SSE maximum compressional stress and near NE-SW minimum extensional stress, while the stress regimes are mainly of strike slip, part of the reverse-fault type. Recent tectonic stress field in the region is characterized by horizontal components. The maximum principal compression stress direction was from NEE to SEE, the average principal compression stress direction was near NWW-SSE maximum compres- sional stress and near NE-SW minimum extensional. The recent tectonic stress field of the studied area can be controlled by a large tectonic stress area.

Numerical calculations of tectonic stress field of Chinese mainland and its neighboring regions and their applications to explanation of seismic activity

This paper made a numerical simulation to the basic tectonic stress field of Chinese mainland and its neighboringregion using the visco-elasticity finite element model and the new published displacement rate result. Main contents include the simulation of maximum shear stress and its varying rate, the maximum shear strain and its varyingrate, the shear strain energy density and its varying rate. In view of the high inhomogeneous distribution characterof seismicity in space and time in Chinese mainland and its neighboring area, the normalized background energyvalue was given by means of normalized treatment to the earthquake energy release in the eastern and westernparts of Chinese mainland. And the comparison of the simulation result with the actual seismicity was made. Thefesults show that the simulation values can explain well the earthquake distribution character of Chinese mainlandand its neighboring area.

Numerical modeling of tectonic stress field and fault activity in North China

On the basis of a 3-dimension visco-elastic finite element model of lithosphere in North China, we numerically simulate the recent mutative figures of tectonic stress field. Annual change characteristics of stress field are： 1 ） Maximum principal tensile stress is about 3 -9 kPaa-1 and its azimuth lie in NNW-SSE. 2） Maximum principal compressive stress is about 1 - 6 kPaa-1 and its azimuth lie in NEE-SWW. 3 ） Maximum principal tensile stress is higher both in the west region and Liaoning Province. 4） Variation of tectonic stress field benefits fault movement in the west part and northeast part of North China. 5 ）Annual accumulative rates of Coulomb fracture stress in Tanlu fault belt have segmentation patterns： Jiashan-Guangji segment is the high- est （6 kPaa - 1 ） , Anshan-Liaodongwan segment is the second （5 kPaa - l ） , and others are relatively lower （ 3 - 4 kPaa-1 ）.