江苏及邻区地震重新定位和构造特征分析

Relocation of earthquakes in Jiangsu and neighboring areas,China and analysis of structural features

本文将双差定位和遗传算法定位两种方法相结合,对江苏及邻区1980-2005年的地震进行重新定位研究.重新定位后大大改善了原地震定位的精度,地震在空间上更加集中分布在某些区域,地震震源深度分布结果更加合理.江苏及邻区地震主要发生在上地壳和中地壳;研究区不同构造单元的震源深度统计分析表明,下扬子断块江苏段、冀鲁断块和豫皖断块的地震震源深度特点相似,在10-11km、15-17km深处存在二个明显的地震优势分布,推测分别在上地壳底面和中地壳;在25km深处也存在一小的地震优势分布面,但地震频次较低.大别山地区地震的震源深度与下扬子断块、冀鲁断块和豫皖断块内的地震震源深度存在明显的差异,主要差异为大别山地区10km以上的浅源地震十分发育,在6-7km的深处有一地震优势分布,该深度附近地震波速度可能较高,而在10km以下差异不大.

The earthquakes happened in and around Jiangsu province from 1980 to 2005 were relocated precisely by using Double-Difference （DD） method and Genetic Algorithm （GA）. The result shows that the earthquakes are more concentrated in some areas and the distribution of focal depth is more reasonable. Most earthquakes happened in the upper and middle crust. The distributions of focal depths are similar basically for Lower Yangtze Block, Hebei-Shandong Block and Henan-Anhui Block. There are two predominant depths： 10 11 km and 15 - 17 km, where more earthquakes happened. We infer that they are in the bottom of upper crust and in middle crust respectively. At 25 km, there is a minor predominant focal depth. In Dabie Orogenic Zone, most focal depths are less than 10 km, especially, concentrate in 6 - 7 km. Maybe there is high velocity in that depths. The shallower focal depth is the major feature of Dabie Orogenic Zone different from other tectonic provinces as mentioned above, but below 10 km they have similar features.