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
Based on the analyses of grouped activity features of deep-focus (M≥6.0) and shallow-focus (M S≥5.0) earthquakes in the Northeast China region, the time-space correlation between deep focus “strong earthquake group...Based on the analyses of grouped activity features of deep-focus (M≥6.0) and shallow-focus (M S≥5.0) earthquakes in the Northeast China region, the time-space correlation between deep focus “strong earthquake group" and shallow focus “strong earthquake group" have been studied. The study was mainly on the characteristics of earthquake distribution on the collision zone between the west Pacific plate and the Eurasian plate and on its relations to the morphological feature of the western Pacific subduction zone. Moreover, emphasis was laid on analysis of the effect of the west Pacific plate on the seismicity of Eurasian plate. It is shown that in the region where the west Pacific plate subducts at low angles, the seismicity on the plate collision zone is strong, the effect of plate subduction on Eurasian continent is strong too, and the subduction zone is under a state of high compressional stress. However, in the region where the west Pacific plate subducts at high angles, the seismicity along the plate collision zone is weak, the effect of plate subduction on Eurasian continent is weak too, and the tensile stress produced by the subduction zone at depth is enhanced. We therefore propose that the seismicity in the northeast China region will enter an active period of shallow “strong earthquake group" in the future 10 years. In the period, six earthquakes of M S≥5.0 may occur. Therefore, the work of earthquake monitoring and prediction in this region shall be strengthened.展开更多
By taking moderate-strong earthquakes in South,North and West China as the research subjects and taking into consideration the fault strikes in these regions,this paper selects 8 kinds of seismology indexes with clear...By taking moderate-strong earthquakes in South,North and West China as the research subjects and taking into consideration the fault strikes in these regions,this paper selects 8 kinds of seismology indexes with clear physical significance and strong independence to carry out spatial scanning of the parallel,vertical and oblique slip of fault along the fault strike.Based on the size of correlation coefficients between the scanning curve and source region curve we quantitatively analyze the difference between scan results among different slip modes and study the impact of fault strike in different tectonic divisions on scanning results and variation rules of seismological parameters.The results show that not only does the change of spatial parameters have a great influence on seismological parameter scanning,but so does the fault strike in the source region.This paper presents the optimum condition parameters with least spatial influencing scanning scope for different magnitude seismology indexes and analyzes the possible influence of fault strike on seismological parameter scanning results.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.
文摘Based on the analyses of grouped activity features of deep-focus (M≥6.0) and shallow-focus (M S≥5.0) earthquakes in the Northeast China region, the time-space correlation between deep focus “strong earthquake group" and shallow focus “strong earthquake group" have been studied. The study was mainly on the characteristics of earthquake distribution on the collision zone between the west Pacific plate and the Eurasian plate and on its relations to the morphological feature of the western Pacific subduction zone. Moreover, emphasis was laid on analysis of the effect of the west Pacific plate on the seismicity of Eurasian plate. It is shown that in the region where the west Pacific plate subducts at low angles, the seismicity on the plate collision zone is strong, the effect of plate subduction on Eurasian continent is strong too, and the subduction zone is under a state of high compressional stress. However, in the region where the west Pacific plate subducts at high angles, the seismicity along the plate collision zone is weak, the effect of plate subduction on Eurasian continent is weak too, and the tensile stress produced by the subduction zone at depth is enhanced. We therefore propose that the seismicity in the northeast China region will enter an active period of shallow “strong earthquake group" in the future 10 years. In the period, six earthquakes of M S≥5.0 may occur. Therefore, the work of earthquake monitoring and prediction in this region shall be strengthened.
基金sponsored by sub-project ofNotional Key Technology R&D Program (2006BAC01B020105)the Key Technology R&D Program of AnhuiProvince (08010302204),China
文摘By taking moderate-strong earthquakes in South,North and West China as the research subjects and taking into consideration the fault strikes in these regions,this paper selects 8 kinds of seismology indexes with clear physical significance and strong independence to carry out spatial scanning of the parallel,vertical and oblique slip of fault along the fault strike.Based on the size of correlation coefficients between the scanning curve and source region curve we quantitatively analyze the difference between scan results among different slip modes and study the impact of fault strike in different tectonic divisions on scanning results and variation rules of seismological parameters.The results show that not only does the change of spatial parameters have a great influence on seismological parameter scanning,but so does the fault strike in the source region.This paper presents the optimum condition parameters with least spatial influencing scanning scope for different magnitude seismology indexes and analyzes the possible influence of fault strike on seismological parameter scanning results.
