摘要
本文结合1992年01月至2012年10月国家地震台网、四川地震台网、云南地震台网及重庆地震台网的65个台站记录到的2,107个地震的17,945条P波绝对到时数据及227,701条P波相对到时数据,利用双差地震层析成像方法联合反演了昭通地区地震震源参数及地壳三维速度结构.反演结果表明,地震重定位精度有了显著改进,地震在水平方向的重定位精度要高于垂直方向.在深度方向,消除了重定位前地震在5~10km间的层状分布假象,昭通地区震源深度总体大于彝良地区,且彝良地区地震随深度增加向西展布,根据余震分布特征推测地震发生在走向NNE,倾向NW的石门断裂上.反演得到的三维速度结构表明,地表速度异常与地形起伏及地质特征有着密切关系：在浅层,昭通坳陷盆地表现为较大范围的低速异常,且低速异常区在盆地东北缘范围加深.彝良附近表现为高速异常带,大关附近表现为低速异常.随着深度的增加,反演得到的P波三维速度结构清晰地显示出彝良地区中下地壳介质受到北东向挤压而向上隆起,与浅部的高、低速异常区相互交错,形成介质速度构造复杂区域.重定位后的彝良ML5.7级和ML5.6级地震的震源位于隆起的高速异常区两侧的速度过渡区,其走滑兼逆冲的破裂机制与该处反演结果揭示的彝良地区下方的速度异常形成机制较为一致.
In this study,the double difference seismic tomography method is applied to 17,945 absolute P wave first arrival times and 227,701 high quality relative P wave first arrival times to determine the absolute and relative hypocenter parameters of 2,107 seismic events as well as detailed 3D crustal velocity structure at the Zhaotong region.The data was recorded by 65 stations of China national seismic network,Sichuan seismic network,Yunnan seismic network and Chongqing seismic network from January 1992 to October 2012.The events relocation result shows that,the accuracy of events relocation are significantly improved,which is higher in horizontal direction.After relocating,the layered hypocenter distribution between 5 km and 10 km before relocation has disappeared.In general,the focal depths at Zhaotong area are deeper than those in Yiliang area,and the relocated events distribute westward with the depth increasing in Yiliang area.From the hypocentral distribution of relocated aftershocks we infer that the Yiliang seismic sequences locate in the NNE strike Shimen fault with NW dip.The velocity structure results show that,the inferred velocity structure of earth surface correlates well with the surface geological and topographic features：in superficial layer,Zhaotong down warping basin shows a large range low velocity anomaly,and the range of low velocity zone become greater in the northeast edge of Zhaotong basin.The area near Yiliang shows high velocity anomaly,while the Daguan area shows low velocity anomaly.With the depth increasing,the inversed P wave velocity structure shows clearly that the medium of the middle and lower crust swell up due to the NE compression,and interlace with high and low velocity anomaly in superficial layer,which compose complex velocity structure zone.The hypocenters of relocated Yiliang ML5.7 and ML5.6 earthquakes focus locate in the transition zone from the both sides of the uplift high velocity zone.The focal mechanism of Yiliang ML5.7 and ML5.6 earthquakes is strike slip,with a small thrust component,which agrees with the velocity anomaly formation mechanism revealed by inversed result.
出处
《地球物理学进展》
CSCD
北大核心
2014年第4期1573-1580,共8页
Progress in Geophysics
基金
国家自然科学基金(41374105
41274068)
中国科学院知识创新工程重要方向项目(KZCX2-EW-QN603)共同资助
关键词
双差地震层析成像
昭通地区
重定位
三维速度模型
彝良地区
double-difference seismic tomography method
Zhaotong region
relocation
3D velocity structure
Yiliang area
