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Based on the theories of continuum mechanics and block dynamics, the present study primarily analyzed the tectonic stress field of the main shock faults in the Wenchuan Ms 8.0 earthquake happened on May 12, 2008. It discussed the interactions between block-block, block-fault, and fault-fault. The results showed that the strain energy migrates along with the fault propagation. The displacement filed, stress field and the distribution of total strain energy, and the mechanism of the process of the earthquake is explored quantitatively. The results also showed that the Wenchuan Ms 8.0 earthquake changed the tectonic stress field. There is energy concentrated area along the Wenchuan-Maoxian fault after the earthquake, so there should have energy release. [ABSTRACT FROM AUTHOR]

Based on a large set of arrival times of the Pg phase reported by local and regional stations, we estimate azimuthal anisotropy of the Pg-wave velocity in focal volumes of the upper crust in NW Croatia. The method is based on analyses of the azimuthal dependence of ratios of cumulative differences of arrival times and travel paths between foci of earthquake pairs, computed for rays propagating within narrow azimuthal windows. The results clearly indicate the presence of anisotropy of 3.3% with the direction of fast velocity (approximately NNE-SSW) coinciding with the direction of the maximum tectonic pressure as revealed by 23 available focal mechanisms and previous geological investigations. Although a large part of observed anisotropy can be explained assuming that focal volumes are pervaded by a system of vertical extensive-dilatancy anisotropy (EDA) cracks aligned under the influence of local tectonic stress field, there is indication that — to a smaller extent — some role was also played by alignment of structural features in the region. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with current coal mining operations under a mega-aquifer in NW Bangladesh, and presents a case study of underground mining in Barapukuria. The study uses numerical analyses to evaluate stress redistribution, strata failure, and water inflow enhancements that result from these coal extraction operations. A total of three models (A, B, and C) are presented in this study. Two-dimensional numerical modeling was performed to analyze the deformation and failure behavior of rock elements for two different models (A and B). For model A, we used an elastic finite element software package considering a Mohr–Coulomb failure criterion. For model B, we used boundary element method (BEM). The first two models were applied to determine the stress patterns. Model A provides the tectonic stress pattern of the basin, whereas model B represents the mining-induced stress field. The third model is a schematic model. The results of model A show that tensional failure of rock elements is concentrated in the Gondwana coal sequences as well as within the Eastern Boundary Fault (EBF) and its surroundings. Failure occurs in the middle to lower part of the model, and the magnitude of tensional stress in the shallow part is much greater than in the deeper part. Contours of τ max magnitudes are attributed to up-bending of the overburden, which would create numerous upward propagating fissures/fractures. The results of model B show that fracture propagation would be about 240 m upward for single-slice (height 3 m) mining extraction. From the contours of mean stress magnitudes, it is observed that the high range of fracture propagation increased upward for multi-slice extraction of coal. It is apparent from the fracture heights that large amounts of caving would occur towards the roof due to the multi-slice extraction of coal, and finally would be linked with the water-bearing Dupi Tila Formation. If this happened, it would ultimately cause a major water inflow hazard in the mine. [Copyright &y& Elsevier]

For the study on the relationship between the dynamic phenomena in the mining such as mine earthquakes, outburst and faults slide, firstly, double shear friction experiments of sandstone were made, and its slide criterion was suggested considering the viewing of engineering. Secondly, in order to study the stability of underground rock and zone of tectonic stress field, based on the analysis on distribution characteristic of initial rock stress measurements, the geology structural model was built and tectonic stress field was made a back-analysis by applying finite element method. The calculating results fit with the analysis result of earthquakes mechanism and the distribution characteristic of the measurements. The high stress regional centers station locates discontinuous zone of I level faults and is corresponding to underground earthquakes scene. From then it is certain that tectonic stress is the major origin and necessary condition of mine earthquakes. The instability slide of the faults is the main manifest and the mining activity is the leading factor. Beipiao fault has a dominate effect on other sub faults and tectonic stress area and is dynamical fountain of dynamic phenomena in the Beipiao Mines. [ABSTRACT FROM AUTHOR]

Kunming basin is a Cenozoic faulted basin under the control of mainly SN-trending active faults. In and around the basin, there are a total of eight major active faults. Seismo-geological survey and fault slip observation show that the SN-and NE-trending active faults are mostly sinistral strike-slip faults, while the NW-trending faults are mostly dextral strike-slip faults. Using stress tensor inversion method with 706 active fault striation data at 22 measurement sites, we determined tectonic stress field of the study area. The result shows that modern tectonic stress field in and around Kunming basin is characterized by NNW-SSE compression, ENE-WSW extension, and strike-slip stress regimes. The maximum principal compressional stress ( σ 1) is oriented 335°–2°, with an average dip angle of 21°; the minimum ( σ 3) is oriented 44°∼93°, with an average dip angle of 14°, and the intermediate ( σ 2) has a high, or nearly vertical, dip angle. The inversion result from fault slip data is consistent with the result from focal mechanism solutions. [ABSTRACT FROM AUTHOR]

Using the moment tensor inversion method, we calculate the focal mechanisms of the aftershock sequence of the M S=6.1 Lulong earthquake occurred on October 19, 1982 in Hebei Province. We found that the pressure axis in Lulong basin is nearly in the east-west direction with an azimuth of N74°E. However, in the north of the basin the stress axis changes to N43°E; and in some places near the center of the basin it changes to the northwest that is almost perpendicular to the P axis obtained by us from those events around the basin. This feature illuminates that in Lulong earthquake sequence, the stress direction is different in different parts of crustal structure, which shows that the tectonic movement in Lulong region is complex. This is because that Lulong is located in the eastern part of Chinese mainland and is subject to the compression of Japanese Sea Basin driven by the Pacific Plate. On the other hand, nipped by the Yanshan and North China blocks, Lulong is obviously restricted by the block boundaries. [ABSTRACT FROM AUTHOR]

Inter-crystalline pores, cavities, and fractures created from diagenetic shrinkage of dolomite are inter-connected each other, forming fine oil-and gas-bearing reservoirs. It is hard to predict these complex fracture-cavity reservoirs because of their random distribution, different growth timing, and so on. Taking the lacustrine dolomite fracture-pore reservoir in the Lower Cretaceous Xiagou Formation in the Qingxi oilfield within the Jiuquan basin as an example, we put forward a comprehensive geophysical method to predict carbonate fractures. [ABSTRACT FROM AUTHOR]

We have examined the quality of the National Research Institute for Earth Science and Disaster Prevention (NIED) seismic moment tensor (MT) catalogue obtained using a regional broadband seismic network (FREESIA). First, we examined using synthetic waveforms the robustness of the solutions with regard to data noise as well as to errors in the velocity structure and focal location. Then, to estimate the reliability, robustness and validity of the catalogue, we compared it with the Harvard centroid moment tensor (CMT) catalogue as well as the Japan Meteorological Agency (JMA) focal mechanism catalogue. We found out that the NIED catalogue is consistent with Harvard and JMA catalogues within the uncertainty of 0.1 in moment magnitude, 10 km in depth, and 15° in direction of the stress axes. The NIED MT catalogue succeeded in reducing to 3.5 the lower limit of moment magnitude above which the moment tensor could be reliably estimated. Finally, we estimated the stress tensors in several different regions by using the NIED MT catalogue. This enables us to elucidate the stress/deformation field in and around the Japanese islands to understand the mode of deformation and applied stress. Moreover, we identified a region of abnormal stress in a swarm area from stress tensor estimates. [Copyright &y& Elsevier]

The abundant data of focal mechanism solutions in Tangshan region, China, are inverted for the tectonic stress field. Combined with tectonophysical consideration, the magnitude of the three principal stresses, as well as their vertical variation under the average crustal rock property, in the source region of the 1976 Tangshan earthquake is estimated. The relationship between crustal stress and friction μ c, pore pressure P 0 and stress shape factor Φ is studied. The paper draws the conclusion that the vertical increasing rate of the maximum principal stress σ is directly proportional to friction, and inversely to pore pressure P 0 and stress shape factor Φ; while the vertical increasing rate of the minimum principal tress σ is directly proportional to pore pressure P 0, inversely to friction μ c and stress shape factor Φ. This study is a try to invert the data of focal mechanism solutions for the complete stress tensor. [ABSTRACT FROM AUTHOR]

Based on data of fault movement surveying, we simulate the evolution process of three dimensional stress field in North China by three dimensional finite element method. Evolutional patterns in one-year time scale from 1986 to 1997 have been illustrated and the evolution characteristics of stress field have been analyzed. In comparison with the seismic activity among that time interval in North China, we have primarily discussed the relationship between the evolution of stress field and seismic activity. [ABSTRACT FROM AUTHOR]

Based on the latest result in research on 3D seismic wave velocity structure of crust and uppermost mantle and taking geological setting and fracture zones into consideration, a 3D geological model for the studied region is built up. The boundary constraint and force loading boundary condition for the model are determined according to the characteristics of crustal stress field deduced from earthquake focal mechanism and in-situ stress measurement data. Using linear elastic material model a 3D finite element modeling is conducted to study the characteristics of crustal stress field. A comparison analysis between the simulated stress field and earthquake locations reveals that the moderate and strong earthquakes generally occurred in the zones with high shear stress gradient. Furthermore, the paper notices a few potential earthquake-prone regions. [ABSTRACT FROM AUTHOR]

The orbit perturbation of meteorologic satellite is used for the inversion of stress drop dynamic field of regional crustal structure. Rapid scanning over vast area is carried out to obtain short term earthquake-generating precursor field of seismic source and near-source districts in order to predict the three earthquake elements: epicenter, magnitude and commencement time of earthquake with the same effect as weather forecast. Taking the strong earthquakes that occurred in recent years in the NW of Yunnan as examples, direct deduction has been made for Lijiang and Wuding earthquakes, and curves of dynamic characteristics of stress drop before and after earthquakes as well as abnormal fluctuations of precursor stress drop and commencement time of earthquake have been plotted. [ABSTRACT FROM AUTHOR]

By inversion of fault slip data for Quaternary tectonic stress field and the analysis of crustal deformation after late Teriary, we explained the evolution of crustal dynamic about the north and east margin of Qinghai-Xizang (Tibet) plateau since Miocene. From middle or late Miocene to early Pleistocene, the tectonic stress field was featured by a maximum principal compression which was coming from the collision of India Plate perpendicular to the boundary of the plateau, and was basically of reverse faulting type. Since the late period of early Pleistocene, India Plate continued to push northward and the compressional deformation of the plateau interior increased continuously, meanwhile, NW-SE extension appeared on the east side of the plateau. This formed a favorable condition for the interior block of the plateau to slide towards east and southeast, causing the faults surrounding the plateau to change from thrust to strike-slip. The contemporary tectonic stress field was formed from the late period of early Pleistocene and continued to present. The direction of maximum principal compressional stress rotated clockwise with respect to the previous tectonic stress field, the stress field was mainly of strike-slip type. [ABSTRACT FROM AUTHOR]

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 are simulated by finite element method. Then the overall characteristics and regional specific feature of North China are studied. Finally, the influences of the valid dynamic boundary conditions of North China Block, active faults and the inhomogeneity of crustal medium on tectonic stress field of North China are investigated. [ABSTRACT FROM AUTHOR]

This paper made a numerical simulation to the basic tectonic stress field of Chinese mainland and its neighboring region 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 varying rate, the shear strain energy density and its varying rate. In view of the high inhomogeneous distribution character of seismicity in space and time in Chinese mainland and its neighboring area, the normalized background energy value was given by means of normalized treatment to the earthquake energy release in the eastern and western parts of Chinese mainland. And the comparison of the simulation result with the actual seismicity was made. The results show that the simulation values can explain well the earthquake distribution character of Chinese mainland and its neighboring area. [ABSTRACT FROM AUTHOR]

Genetic algorithm-finite element method (GA-FEM) is applied to the study of tectonic stress field of part of East Asia area. From the observed stress distribution, 2-D elastic plane stress inversion is made to deduce the boundary forces and investigate controlling factors. It is suggested that the continent-continent collision is the dominant factor controlling the Chinese tectonic stress field. The ocean-continent convergence along the subduction zone is an important factor. There exists tensile boundary force along the marginal sea. [ABSTRACT FROM AUTHOR]