【摘要】 利用hypo2000和hypoDD程序对滇东南弧形构造带1990—2011年间的小震进行了重新定位和精定位;精定位后水平误差≤1.4km,垂直误差≤1.9km。在此基础上,根据P珔波和S珔波最大振幅比法,得到区内2007—2012年间148个小震的震源机制解。研究表明,正-走滑滑动性质的节面数几乎为逆-走滑的2倍,显示该区现今构造活动以正-走滑性质为主。根据精定位后的小震震源深度剖面特征,曲江断裂、石屏-建水断裂倾向SW,红河断裂倾向NE,与该地区地壳速度结构剖面所反映的断裂几何学特征一致。在大陆动力学背景上,苏门答腊-缅甸海沟的回拉效应影响边界可能已经沿NEE方向深入到曲江断裂和石屏-建水断裂,而川滇块体SSE向的推挤作用在滇东南弧形构造带可能已居于次要地位,与SSE-NNW向的挤压作用相比,SWW-NEE向的拉张效应在滇东南现今构造活动中起着更重要的作用。这样的构造动力学背景与小震震源参数的总体特征所反映的构造力学环境也是一致的,滇东南弧形构造带可能是一个正在形成的张-剪性构造区。更多还原

【Abstract】 The accurate relocations of small earthquakes during 1990-2011 on the arcuate tectonic belt in southeast Yunnan(23°N to 25°N,101°E to 103°E)are obtained by hypo2000 and double difference algorithm using Pg and Sg phase readings of 721 earthquakes recorded by Yunnan Earthquake Network Center.The RMS residual decreases to 0.45 from 1.43 with an average precision of about 1.4km horizontally and 1.9km vertically after relocation. Then we collected the waveform data of the study region during 2007-2012 and calculated the focal mechanisms of 148 small earthquakes with the method of the maximum amplitude ratio between Pg and Sg. Focal mechanism result shows that the number of nodal planes representing normal strike-slip is almost twice of that of the reverse strike-slip,which demonstrates that the dominant movement on the arcuate tectonic belt is normal strike-slip currently. Relocation of small earthquakes greatly improves the definition of the seismic images on the faults that generate them. According to the relocated focal depths,the Qujing Fault and Shiping-Jianshui Fault dip southwest,and the Honghe Fault dips northeast,which are in accord with the fault geometric characteristics revealed by crustal velocity profiles. According to this,the rollback of Sumatra-Myanmar trench has already brought a deep effect on the arcuate tectonics in southeast Yunnan,the compression caused by the slip of Sichuan-Yunnan rhombic block towards SSE may be weakened. So the tensile stress in SWW-NEE direction plays a more important role in present-day activities of the arcuate tectonics compared to the compressive stress in SSE-NNW direction,which can also be deduced from the characteristics of focal mechanism parameters. A transtensional zone may be emerging from the arcuate tectonics in southeast Yunnan.更多还原