The Crust-mantle Structure and Seismic Risk in Tangyin Graben and Its Adjacent Area

1-D and 2-D calculation and interpretation are carried out with the DSS data from the western section of Heze-Changzhi profile and the southern section of Zhengzhou-Jinan profile. 2-D velocity structure is determined in Tangyin graben and its adjacent area. The result shows that velocity structure of the crust and upper mantle is obviously different in vertical and lateral directions. Crustal thickness varies apparently in this area, and there are local low velocity blocks in the interior crust. The swelling M-discontinuity corresponds to Tangyin graben and Moho depth at the highest swelling position is 31 km. Toward the east, its depth gradually increases to 32 km in Xunxian swelling; toward the west, M-discontinuity becomes a steep zone at the piedmont uplift of Taihang Mountain and reaches 40 km at depth near Changzhi. Through analyzing the relationship between historical earthquakes and deep structure in North China, we infer that seismic risk exists in Tangyin graben and its adjacent area.

汤阴地堑及邻区的壳幔结构与地震危险性

利用菏泽－林县－长治剖面西段和郑州－济南剖面南段深地震测深资料，进行一、二维计算与解释，获得了汤阴地堑及邻区的二维速度结构。结果显示：该区地壳上地幔结构在纵、横向上均具有明显的差异。地壳厚度变化大，局部存在低速块体，对应汤阴地堑为一Ｍ面隆起，隆起高点Ｍ面埋深为３１ｋｍ，向东浚县方向，隆起区Ｍ面逐渐加深到３２ｋｍ，向西太行山前方向，隆起区Ｍ面为一陡变带，至长治附近，Ｍ面埋深增至４０ｋｍ。根据华北地区历史地震与深部结构和构造的相关分析认为，汤阴地堑及邻区可能存在发震危险。