Abstract: The phase tensor decomposition techniques and NLCG three-dimensional inversion were used to process a MT profile data，which with 160 km length and across the Hongdong earthquake area of M=8 in 1303，Combined with the Present-Day Crustal Vertical Motion（including GPS and Leveling data）around the study area, the latest geological and geophysical survey results，The conclusions are as follows: Huoshan piedmont fault is an obvious large electrical boundary zone in the study area，In the middle and deep part, it is a low resistivity belt， which runs through the whole scale of the crust，The fault is a NNE trending dextral normal fault, which may be the basement fault dividing Ordos block and North China block. With Huoshan piedmont fault as the boundary, the Ordos block in the West shows a stable tectonic environment, while the lithosphere in the North China block in the East is seriously damaged and there is a trend of thinning. The results of magnetotelluric survey support that the Huoshan piedmont fault was the seismogenic fault of Hongdong earthquake in 1303，The earthquake may occur in the low resistivity body formed by Huoshan piedmont fault, and the focal depth may be between 10-20km. The seismogenic environment of Hongdong earthquake in 1303 may be controlled by multiple factors，The continuous upwelling of asthenosphere materials in the middle and lower crust in the east of Linfen basin caused the regional extension of the North China block，It may be the main controlling factor that leads to the strike slip of Huoshan piedmont fault.

Key words: Magnetotelluric, the 1303 Hongdong M=8 earthquake, Linfen basin, Huoshan Piedmont fault.

摘要： 本文利用相位张量分解技术、三维NLCG反演方法对一条跨过1303年洪洞8级地震区的160km长大地电磁剖面数据进行了分解和反演计算，再结合研究区及其附近的形变场，最新地震地质和地球物理调查结果以及2008年1月到2012年12月之间的小震精定位结果等资料等进行综合分析。研究表明：霍山山前断裂是研究区内明显大型电性边界带，在中深部表现为低阻特征，贯穿了整个地壳尺度，该断裂为NNE走向的右旋正断裂，可能是划分鄂尔多斯地块和华北地块的基底断裂。以霍山山前断裂为界，西侧鄂尔多斯地块表现为稳定的构造环境，而东侧华北地块岩石圈破坏严重且存在着减薄的趋势。大地电磁探测结果支持1303年洪洞8级地震的发震断裂为霍山山前断裂，地震可能发生在霍山山前断裂形成的低阻体中，震源深度可能介于10-20km之间。1303年洪洞8级地震的孕震环境可能受多重因素控制，研究区东侧中下地壳可能存在的的软流圈物质不断上涌引起了华北地块的区域拉张作用，导致霍山山前断裂发生倾向滑动可能是主控因素。

关键词: 大地电磁, 1303年洪洞8级地震, 临汾盆地, 霍山山前断裂