【摘要】 研究地壳构造应力状态及其时空分布特征,特别是应力变化的信息,是探讨地震成因、分析发震条件的重要有效途径之一.本文利用1998年1月至2009年1月以来小江断裂中段及其邻区ML≥2.5的共计740个震源机制解,基于小江断裂中段及其邻近地区地质构造背景,对研究区进行了分区;以该区域内较大地震为界,结合余震时间序列特征,进行时间上的分段;去除较大地震后,采用最长距离聚类分析方法对各分区的地震进行了分类.在此基础上,利用Gephart的应力张量反演方法,根据震源机制解资料反演出了各分区的优势应力场.结果表明,在观测时段内,根据构造和震源机制,可将研究区域分为A和B两个区域.A区最大主应力σ1方位在4个时段内大致为NNW向,B区北部在4个时段内σ1方位大致为NNW向、WNW和ENE向.从应力结构看,A区和B区北部应力以水平作用为主.B区南部σ1方位大致为NNW向,仍以水平作用为主;B区北部σ1方位变化较大,可能与B区北部地质结构复杂、应力调整活跃有关.而A区主应力方位相对稳定,显示了滇中块体的稳定性.更多还原

【Abstract】 The study on temporal and spatial crustal stress change is important for exploring earthquake origin and seismogenic condition.Based on 740 focal mechanism solutions of ML≥2.5 earthquakes occurred during Jan.1998 to Jan.2009 in middle Xiaojiang fault and its adjacent area,the studied region was divided into sub-regions,and temporally further divided into phases with the larger earthquakes as boundary of the sub-regions.After removal of the larger earthquakes this paper inverted the focal mechanism data with the method of Gephart for the stress in main phase of each sub-region.The result indicates that the azimuth of maximum principal stress σ1 in 4 temporal phases of the sub-region A is approximately NNW--SSE,and in northern part of sub-region B are approximately NNW--SSE,WNW--ESE and ENE--WSW.The azimuth of σ1 in southern part of sub-region B is approximately NNW-SSE.The azimuth of σ1 in northern part of sub-region B changed significantly,while the azimuth of σ1 in sub-region A is relatively stable.This result may be related to the complicated structure and possible stress adjusting in northern sub-region B.The σ1 directions in sub-region A may indicate seismically relative stability of the central Yunnan crustal block.更多还原