The South China Sea （SCS） is the largest marginal sea in West Pacific formed by a combined effect of the Eurasian plate, Pacific plate and India-Australian plate, and is thus considered to be a unique natural labora...The South China Sea （SCS） is the largest marginal sea in West Pacific formed by a combined effect of the Eurasian plate, Pacific plate and India-Australian plate, and is thus considered to be a unique natural laboratory to study oceanic dynamics and tectonic evolutions （Xie et al., 2006; Luan and Zhang, 2009）. Besides, the SCS contains enormous petroleum resources for its favorable conditions of oil-gas generation, accumulation and preservation. It is therefore imperative to intensively study the marine in-situ stress and its controlling factors of the SCS.展开更多
A statistic analysis of the characteristics of recent tectonic stress fields in the East China region was performed using 143 sets of data of single focal mechanical solutions of moderate and small earthquakes and 17 ...A statistic analysis of the characteristics of recent tectonic stress fields in the East China region was performed using 143 sets of data of single focal mechanical solutions of moderate and small earthquakes and 17 sets of data of composite focal mechanism solutions. The result shows that at present the East China region is controlled by an ENE-（ about 80°） oriented principal compressive and NNW-（about 350°） oriented principal tensile stress field. The effect mode of the principal stress is mainly horizontal and sub-horizontal. In a background of basic consistency of the direction and effect mode of stress field, the existence of different seismotectonic zones may be related to the distribution of major active faults in the relevant areas. It indicates the effect and control of the existing structures on the seismic dislocation. Analysis of focal mechanism solution data of recent moderate and small earthquakes and directions of long axes of isoseismal contours of historic moderate and strong earthquakes and recent felt earthquakes indicates that seismic rupture and dislocation in East China region occurred mainly along the faults in NE and NW directions, and sometimes in NNE, ENE, WNW or near-WE directions. Movement along the seismic faults is mainly strike-slip or nearstrike-slip, with a less oblique slip component. Regional difference in dislocation modes exist along the seismic faults. The historical moderate and strong earthquakes in East China produced mainly NE-trending ruptures and dislocations, while the recent earthquakes produced NW-SE ruptures and dislocations in the land region and NE and NW ones in the sea areas.展开更多
The hydrofracturing technique has developed into a reliable and practical method for determining the original three-dimensional crustal stress state of underground caverns,the load-bearing capacity of a high pressure ...The hydrofracturing technique has developed into a reliable and practical method for determining the original three-dimensional crustal stress state of underground caverns,the load-bearing capacity of a high pressure cavern itself,and the high pressure hydraulic permeability of rock masses,and has also been extensively used in disposal of nuclear waste,long and deeply-buried traffic channels and high-pressure cavern engineering for hydraulic power plants.The practice shows that the comprehensive measurement of the physical parameters of the rock mass and taking full use of the wall rock load-bearing capacity to optimize the engineering design hold are very useful in ensuring the engineering safety and improving the design level.展开更多
The crustal stress and seismic hazard estimation along the southwest segment of the Longmenshan thrust belt after the Wenchuan Earthquake was conducted by hydraulic fracturing for in-situ stress measurements in four b...The crustal stress and seismic hazard estimation along the southwest segment of the Longmenshan thrust belt after the Wenchuan Earthquake was conducted by hydraulic fracturing for in-situ stress measurements in four boreholes at the Ridi, Wasigou, Dahegou, and Baoxing sites in 2003, 2008, and 2010. The data reveals relatively high crustal stresses in the Kangding region （Ridi, Wasigou, and Dahegou sites） before and after the Wenchuan Earthquake, while the stresses were relatively low in the short time after the earthquake. The crustal stress in the southwest of the Longmenshan thrust belt, especially in the Kangding region, may not have been totally released during the earthquake, and has since increased. Furthermore, the Coulomb failure criterion and Byerlee＇s law are adopted to analyzed in-situ stress data and its implications for fault activity along the southwest segment. The magnitudes of in-situ stresses are still close to or exceed the expected lower bound for fault activity, revealing that the studied region is likely to be active in the future. From the conclusions drawn from our and other methods, the southwest segment of the Longmenshan thrust belt, especially the Baoxing region, may present a future seismic hazard.展开更多
DSS data of the last twenty years and more in the northern part of North China are further interpreted, and combined with other geological and geophysical data, the crustal model for the 3 D finite element method is ...DSS data of the last twenty years and more in the northern part of North China are further interpreted, and combined with other geological and geophysical data, the crustal model for the 3 D finite element method is built after straticulate crustal structure and elastic mechanics parameters are obtained. Referring to regional tectonic stress field and taking the effect of gravity into account, the paper constrains properly the model boundary and then computes the displacement of each nodal point and the strain and stress of each element by using the program from the 3 D linear elastic finite method. The relationship between the distribution feature of the crustal stress field and seismicity is discussed on the basis of analyzing contour maps of maximum principal compressive stress in the upper, middle and lower crusts.展开更多
A new method of detecting stress change by temperature(DSCT),has been recently proposed on the basis of the experimental results in laboratory,and verified by field observation.In this paper,at first,physical backgrou...A new method of detecting stress change by temperature(DSCT),has been recently proposed on the basis of the experimental results in laboratory,and verified by field observation.In this paper,at first,physical background is concisely introduced,and experimental researches are followed.Then,the key techniques are reviewed,and the main results on in-situ observations are also given in detail.At last,we emphasize on the prospects of this method for being investigated further.The potential prospect includes six contents:(1)to observe the tidal force and its secondary fluid thermal effect;(2)to study temperature response to change in direction of the stress change;(3)to carry out practical engineering application;(4)to analyze the strong earthquake risk,based on bedrock temperature observation;(5)to conduct in situ experiment on DSCT;(6)to explain quantitatively the satellite thermal infrared anomaly.In short,considering that the dynamic change of the crustal stress is a key parameter of earthquake forecasting or engineering application,the method of DSCT has important practical significance for earthquake risk or engineering applications.展开更多
Based on the shear wave splitting analysis of the seismic recordings at 17 temporary stations and three permanent stations, we measured the shear wave splitting parameters(i.e., the polarization direction of fast shea...Based on the shear wave splitting analysis of the seismic recordings at 17 temporary stations and three permanent stations, we measured the shear wave splitting parameters(i.e., the polarization direction of fast shear wave and the time delay of slow wave) to perform a systematic analysis of the crustal seismic anisotropy around the Longmenshan fault in the 2013 M7.0 Lushan earthquake region. We observed apparent spatio-temporal characteristics in the shear wave splitting parameters. The spatial distribution of fast polarization directions showed a clear partitioning in the characteristics from northwest to southeast in the focal region,which changed from NW-SE to NE-SW. In the northwest of the focal region, the fast polarization direction was oriented to NW-SE, which was parallel to the maximum horizontal compressive stress direction. However, the NE-SW fast polarization direction in the southeast of the focal region was parallel to the Longmenshan fault strike. For station BAX on the Central fault in the middle of the focal region, the distribution of fast polarization directions showed a bimodal pattern, with one dominant in the NE-SW direction and the other in the NW-SE direction. With regard to the temporal variation, the time delays were large in the initial stage after the mainshock but then gradually decreased over time and tended to be stable in the later period. This indicated that stress in the focal region increased to a maximum when the main shock occurred, with the stress release caused by the mainshock and aftershock activity, and the stress gradually decreased after a period of time. The scatter of fast polarization directions was large after the main shock, but over time the scatter gradually decreased, indicating that the Lushan earthquake caused a large perturbation in the local stress field. As the stress gradually decreased and was adjusted by the aftershock activity, the perturbation gradually weakened.展开更多
The relationship between the earth stress field, earth surface displacement field and the gravity variation is deduced. Algorithms based on the boundary element method to compute the earth stress variation using the e...The relationship between the earth stress field, earth surface displacement field and the gravity variation is deduced. Algorithms based on the boundary element method to compute the earth stress variation using the earth surface displacement is discussed. The stress field variation in Jiashi region, Xinjiang, China is obtained from the GPS data observed in 1997 and 1998, respectively, and the relationship among the local stress field variation, seismic activities and fault tectonic activities is discussed.展开更多
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-...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.展开更多
On the basis of the synthetic analysis of present regional tectonic stress field in China, this paper follows three steps to do crustal stability assessment: (1) zonation of preevaluation area for regional crustal sta...On the basis of the synthetic analysis of present regional tectonic stress field in China, this paper follows three steps to do crustal stability assessment: (1) zonation of preevaluation area for regional crustal stability assessment and zonation; (2) choice, taking value and weight distribution of quantitative evaluation indices and determination of evaluation standards; (3) assessment and zonation of regional crustal stability using fuzzy mathematics in China.展开更多
基金supported by the project of the China Geological Survey(Grant No.1212011220122)
文摘The South China Sea （SCS） is the largest marginal sea in West Pacific formed by a combined effect of the Eurasian plate, Pacific plate and India-Australian plate, and is thus considered to be a unique natural laboratory to study oceanic dynamics and tectonic evolutions （Xie et al., 2006; Luan and Zhang, 2009）. Besides, the SCS contains enormous petroleum resources for its favorable conditions of oil-gas generation, accumulation and preservation. It is therefore imperative to intensively study the marine in-situ stress and its controlling factors of the SCS.
文摘A statistic analysis of the characteristics of recent tectonic stress fields in the East China region was performed using 143 sets of data of single focal mechanical solutions of moderate and small earthquakes and 17 sets of data of composite focal mechanism solutions. The result shows that at present the East China region is controlled by an ENE-（ about 80°） oriented principal compressive and NNW-（about 350°） oriented principal tensile stress field. The effect mode of the principal stress is mainly horizontal and sub-horizontal. In a background of basic consistency of the direction and effect mode of stress field, the existence of different seismotectonic zones may be related to the distribution of major active faults in the relevant areas. It indicates the effect and control of the existing structures on the seismic dislocation. Analysis of focal mechanism solution data of recent moderate and small earthquakes and directions of long axes of isoseismal contours of historic moderate and strong earthquakes and recent felt earthquakes indicates that seismic rupture and dislocation in East China region occurred mainly along the faults in NE and NW directions, and sometimes in NNE, ENE, WNW or near-WE directions. Movement along the seismic faults is mainly strike-slip or nearstrike-slip, with a less oblique slip component. Regional difference in dislocation modes exist along the seismic faults. The historical moderate and strong earthquakes in East China produced mainly NE-trending ruptures and dislocations, while the recent earthquakes produced NW-SE ruptures and dislocations in the land region and NE and NW ones in the sea areas.
基金National Natural Science Fund Significant Project:Study onthe Secular Deformation of Soft Rocks in Deeply-buried Long Tunnel under Effect of Durative High Crustal Stress (90302011)
文摘The hydrofracturing technique has developed into a reliable and practical method for determining the original three-dimensional crustal stress state of underground caverns,the load-bearing capacity of a high pressure cavern itself,and the high pressure hydraulic permeability of rock masses,and has also been extensively used in disposal of nuclear waste,long and deeply-buried traffic channels and high-pressure cavern engineering for hydraulic power plants.The practice shows that the comprehensive measurement of the physical parameters of the rock mass and taking full use of the wall rock load-bearing capacity to optimize the engineering design hold are very useful in ensuring the engineering safety and improving the design level.
基金supported by the Fund of the Institute of Geomechanics (No. DZLXJK201107)the National Scientific Program of China-Experimental Study on the Technique of In-Situ Stress Measurements and Monitoring (No. SinoProbe-06-03)the auspice of National Key Basic Project (973) (No. 2008CB425702)
文摘The crustal stress and seismic hazard estimation along the southwest segment of the Longmenshan thrust belt after the Wenchuan Earthquake was conducted by hydraulic fracturing for in-situ stress measurements in four boreholes at the Ridi, Wasigou, Dahegou, and Baoxing sites in 2003, 2008, and 2010. The data reveals relatively high crustal stresses in the Kangding region （Ridi, Wasigou, and Dahegou sites） before and after the Wenchuan Earthquake, while the stresses were relatively low in the short time after the earthquake. The crustal stress in the southwest of the Longmenshan thrust belt, especially in the Kangding region, may not have been totally released during the earthquake, and has since increased. Furthermore, the Coulomb failure criterion and Byerlee＇s law are adopted to analyzed in-situ stress data and its implications for fault activity along the southwest segment. The magnitudes of in-situ stresses are still close to or exceed the expected lower bound for fault activity, revealing that the studied region is likely to be active in the future. From the conclusions drawn from our and other methods, the southwest segment of the Longmenshan thrust belt, especially the Baoxing region, may present a future seismic hazard.
文摘DSS data of the last twenty years and more in the northern part of North China are further interpreted, and combined with other geological and geophysical data, the crustal model for the 3 D finite element method is built after straticulate crustal structure and elastic mechanics parameters are obtained. Referring to regional tectonic stress field and taking the effect of gravity into account, the paper constrains properly the model boundary and then computes the displacement of each nodal point and the strain and stress of each element by using the program from the 3 D linear elastic finite method. The relationship between the distribution feature of the crustal stress field and seismicity is discussed on the basis of analyzing contour maps of maximum principal compressive stress in the upper, middle and lower crusts.
基金supported by the National Natural Science Foundation of China (Grant No.42274079)by the Basic Research Funds from the Institute of Geology,China Earthquake Administration (Grant No.IGCEA1815).
文摘A new method of detecting stress change by temperature(DSCT),has been recently proposed on the basis of the experimental results in laboratory,and verified by field observation.In this paper,at first,physical background is concisely introduced,and experimental researches are followed.Then,the key techniques are reviewed,and the main results on in-situ observations are also given in detail.At last,we emphasize on the prospects of this method for being investigated further.The potential prospect includes six contents:(1)to observe the tidal force and its secondary fluid thermal effect;(2)to study temperature response to change in direction of the stress change;(3)to carry out practical engineering application;(4)to analyze the strong earthquake risk,based on bedrock temperature observation;(5)to conduct in situ experiment on DSCT;(6)to explain quantitatively the satellite thermal infrared anomaly.In short,considering that the dynamic change of the crustal stress is a key parameter of earthquake forecasting or engineering application,the method of DSCT has important practical significance for earthquake risk or engineering applications.
基金supported by the National Natural Science Foundation of China (Nos. 41774061 and 41474088)the Special Fund of the Institute of Geophysics,China Earthquake Administration (No. DQJB17B10)
文摘Based on the shear wave splitting analysis of the seismic recordings at 17 temporary stations and three permanent stations, we measured the shear wave splitting parameters(i.e., the polarization direction of fast shear wave and the time delay of slow wave) to perform a systematic analysis of the crustal seismic anisotropy around the Longmenshan fault in the 2013 M7.0 Lushan earthquake region. We observed apparent spatio-temporal characteristics in the shear wave splitting parameters. The spatial distribution of fast polarization directions showed a clear partitioning in the characteristics from northwest to southeast in the focal region,which changed from NW-SE to NE-SW. In the northwest of the focal region, the fast polarization direction was oriented to NW-SE, which was parallel to the maximum horizontal compressive stress direction. However, the NE-SW fast polarization direction in the southeast of the focal region was parallel to the Longmenshan fault strike. For station BAX on the Central fault in the middle of the focal region, the distribution of fast polarization directions showed a bimodal pattern, with one dominant in the NE-SW direction and the other in the NW-SE direction. With regard to the temporal variation, the time delays were large in the initial stage after the mainshock but then gradually decreased over time and tended to be stable in the later period. This indicated that stress in the focal region increased to a maximum when the main shock occurred, with the stress release caused by the mainshock and aftershock activity, and the stress gradually decreased after a period of time. The scatter of fast polarization directions was large after the main shock, but over time the scatter gradually decreased, indicating that the Lushan earthquake caused a large perturbation in the local stress field. As the stress gradually decreased and was adjusted by the aftershock activity, the perturbation gradually weakened.
基金State Natural Science Foundation of China !(49774214)the State Key Project !(96-913-07).
文摘The relationship between the earth stress field, earth surface displacement field and the gravity variation is deduced. Algorithms based on the boundary element method to compute the earth stress variation using the earth surface displacement is discussed. The stress field variation in Jiashi region, Xinjiang, China is obtained from the GPS data observed in 1997 and 1998, respectively, and the relationship among the local stress field variation, seismic activities and fault tectonic activities is discussed.
文摘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.
文摘On the basis of the synthetic analysis of present regional tectonic stress field in China, this paper follows three steps to do crustal stability assessment: (1) zonation of preevaluation area for regional crustal stability assessment and zonation; (2) choice, taking value and weight distribution of quantitative evaluation indices and determination of evaluation standards; (3) assessment and zonation of regional crustal stability using fuzzy mathematics in China.
