沧州地区地壳上地幔的远震P波三维速度结构成像
Teleseismic P Wave Tomography on the Crustal and Upper Mantle Structure in Cangzhou Area
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摘要: 利用架设在沧州地区的20台流动地震台站于2006年12月至2010年7月间记录的271个远震事件,读取的2308个P波到时数据,采用地震层析成像方法反演得到沧州及其邻区(38.0°N~39.0°N,116.5°E~117.5°E)的地壳上地幔P波三维速度结构。层析成像结果表明,沧东断裂两侧的地壳介质的速度分布表现出明显的横向差异,浅层速度分布同地表地质结构分布相一致。沧东断裂西北侧沧县隆起的地壳速度较高,表明其基底抬升;断裂带东南边的黄骅拗陷速度较低,说明基底埋藏较深。本文的远震层析成像研究结果和前人使用重力、电磁和人工地震的探测结果都表明,沧东断裂带两侧的地质构造和地球物理性质有明显的变化,这种构造差异在整个地壳中都有体现。Abstract: We used 2308 P wave arrival times from 271 teleseismic events recorded by the 20 portable seismic stations during December 2006 to July 2010 in Cangzhou region, Hebei Province. By using seismic tomography method, we got the 3-D crustal and upper mantle P wave velocity structure in Cangzhou and its adjacent area (38.0°N~39.0°N, 116.5°E~117.5°E). Teleseismic tomography results reveal that the significant lateral variations for the velocity distributions in crust on both sides of Cangdong fault zone. The shallow velocity distribution is consistent with the distribution of the surface geological structure. Cangxian uplift in the northwest of Cangdong fault zone is with the higher velocity values in the crust, indicating that it has the uplift basement. Huanghua depression in the southeast of the fault zone is with lower velocity, indicating the substrate buried deeper. These results and previous gravity, electromagnetic and artificial seismic exploration results all show that the Cangdong fault zone is in obvious changes in the geological structure and geophysical properties, which could be displayed in whole crust.