上海及周边地区地壳精细速度结构体波双差成像

Crustal structure of Yangtze River Delta using tomoDD and its implication for seismicity

利用江浙沪区域地震台网53个台站在1983—2015年间记录的1595个中小地震事件,筛选出54248个直达P、S震相,采用双差层析成像方法,同时获得了下扬子地区三维地壳P、S波速度结构和地震精定位结果,然后对该区地震活动与速度结构分布的关系进行了研究.检测版测试显示,除边缘区域外,0.5°大小网格可以对研究区内部进行较好的分辨.速度结构分布图像结果显示研究区西部陆域和东北部海域的中下地壳存在明显的低速层.此处也是历史上多次强震活跃的地方,如1984如东近海M 6.2、6.1地震,1979溧阳M 6.0,1996长江口外M 6.1地震.综合分析认为,下扬子地区强震活动区域与该区中上地壳速度结构异常体分布相关,强震发生在高速区与低速区交界处.

By using the Double Difference Topography Method(tomoDD), we obtained 3 D crustal structure of Vp and Vs of Yangtze River Delta, the relocated hypocenters were also received at the same time. There are about 1595 seismic rays from 1983—2015 recorded by 53 stations in eastern China,which was utilized in this study. The checkboard test showed that it can be resolved well in the study area with 0.5° grid meshed, except for the marginal zone. The results of tomoDD indicate that there are a lower P and S wave velocity layer in the 10~20 km depth underneath the northern Lower Yangtze Zone, and it’s coincide with the active epicenters zone.From the horizontal slices of 3 D Crustal velocity images we found that, the three modern strong earthquakes(1979 M 6.0, 1984 M 6.2,1996 M 6.1) in the Lower Yangtze Zone occurred all inside or the border of the lower velocity layer. The research results suggest again that,crustal shallow strong earthquakes are not irregular distributed but tend to nuclear above or around the crustal lower velocity layer.