With waveform data of 613 earthquakes with ML ≥ 2. 5 in the middle section of the Xiaojiang fault and its adjacent area which occurred during January,1998 to September 2007,focal mechanisms were calculated by the dir...With waveform data of 613 earthquakes with ML ≥ 2. 5 in the middle section of the Xiaojiang fault and its adjacent area which occurred during January,1998 to September 2007,focal mechanisms were calculated by the direct wave amplitude ratio of S /P in the vertical component and their characteristics were analyzed. According to regional tectonic features of the middle section of the Xiaojiang fault and its adjacent area,the study region was partitioned into two zones with the Xiaojiang fault as the boundary,e. g. zone A and zone B (including the Xiaojiang fault). In order to research the faults stress in detail,the Xiaojiang fault zone was picked out for independent analysis. The study region was also partitioned into 1°× 1° cells with a 0. 5° step. The stress fields of zone A,B and the fault zone were inverted with the FMSI method (Gephart,1990). The results show that first, the faults are mainly of strike-slip in the middle section and its adjacent area,amounting to 81. 28%,69. 23% and 72. 97% in the A,B and fault zones,respectively. Secondly,the stress inversion also indicates that the directions of maximum principal stress σ1 in the A, B,and fault zones are approximately NNW,NWW and NWW,the stress action is mainly horizontal,and strike-slip faulting is dominant in the study area. On the other hand,the direction of the principal stress field in the central Yunnan block changed from NNW to NWW,however,in the region between the Yuanmou and Pudu River faults,the azimuth of the main compressive stress shows that the north-south slip is obvious. While the direction of the main compressive stress of the Xiaojiang fault zone is nearly NW; in the east of the Xiaojiang fault,the direction of principal compressive stress is NW to NNW in the eastern Yunnan block.展开更多
Comprehensive statistical analysis was performed on the basic features of focal mechanisms of 619 ML≥2. 0 earthquakes which occurred in the capital circle area from January 2002 to June 2010. By dividing the capital ...Comprehensive statistical analysis was performed on the basic features of focal mechanisms of 619 ML≥2. 0 earthquakes which occurred in the capital circle area from January 2002 to June 2010. By dividing the capital area into three studying regions based on regional tectonic characteristics,cluster analysis was conducted on the focal mechanisms of all subregions using the longest distance method in the statistical cluster analysis to study the characteristics of tectonic stress tensors. The result shows that dominant P-axis azimuth distribution is NNE-NEE and that of T-axis is NNW-NWW,most of the focal areas are controlled by a horizontal stress field and rupture is mainly of horizontal strike-slip. The maximum principal compression stress orientation is NE75° in the west,NE62° in the middle,and near EW in the east of the capital area. The regional tectonic stress field is characterized by horizontal compression.展开更多
基金sponsored by the National Key Technology R&D Program (2006BAC1B03-03-01),Chinathe Joint Earthquake Science Foundation(A07058),China
文摘With waveform data of 613 earthquakes with ML ≥ 2. 5 in the middle section of the Xiaojiang fault and its adjacent area which occurred during January,1998 to September 2007,focal mechanisms were calculated by the direct wave amplitude ratio of S /P in the vertical component and their characteristics were analyzed. According to regional tectonic features of the middle section of the Xiaojiang fault and its adjacent area,the study region was partitioned into two zones with the Xiaojiang fault as the boundary,e. g. zone A and zone B (including the Xiaojiang fault). In order to research the faults stress in detail,the Xiaojiang fault zone was picked out for independent analysis. The study region was also partitioned into 1°× 1° cells with a 0. 5° step. The stress fields of zone A,B and the fault zone were inverted with the FMSI method (Gephart,1990). The results show that first, the faults are mainly of strike-slip in the middle section and its adjacent area,amounting to 81. 28%,69. 23% and 72. 97% in the A,B and fault zones,respectively. Secondly,the stress inversion also indicates that the directions of maximum principal stress σ1 in the A, B,and fault zones are approximately NNW,NWW and NWW,the stress action is mainly horizontal,and strike-slip faulting is dominant in the study area. On the other hand,the direction of the principal stress field in the central Yunnan block changed from NNW to NWW,however,in the region between the Yuanmou and Pudu River faults,the azimuth of the main compressive stress shows that the north-south slip is obvious. While the direction of the main compressive stress of the Xiaojiang fault zone is nearly NW; in the east of the Xiaojiang fault,the direction of principal compressive stress is NW to NNW in the eastern Yunnan block.
基金funded jointly by China Spark Program of Earthquake Science and Technology(XH12001)Special research fund and Task contract of earthquake trend tracing in 2013 of Beijing Earthquake Administration(2013020109)
文摘Comprehensive statistical analysis was performed on the basic features of focal mechanisms of 619 ML≥2. 0 earthquakes which occurred in the capital circle area from January 2002 to June 2010. By dividing the capital area into three studying regions based on regional tectonic characteristics,cluster analysis was conducted on the focal mechanisms of all subregions using the longest distance method in the statistical cluster analysis to study the characteristics of tectonic stress tensors. The result shows that dominant P-axis azimuth distribution is NNE-NEE and that of T-axis is NNW-NWW,most of the focal areas are controlled by a horizontal stress field and rupture is mainly of horizontal strike-slip. The maximum principal compression stress orientation is NE75° in the west,NE62° in the middle,and near EW in the east of the capital area. The regional tectonic stress field is characterized by horizontal compression.
