郯庐断裂带合肥-宿迁段及邻区大地电磁三维成像

Three-dimensional modelling of magnetotelluric data from the Hefei-Suqian segment of the Tanlu Fault Zone,Eastern China

本文利用覆盖郯庐断裂带合肥—宿迁段及邻区的大地电磁阵列数据,应用大地电磁三维反演技术和印模重构方法,获得了测区可靠的三维电阻率模型.该电性模型中,郯庐断裂带东西两侧在浅部均有高阻分布,在深部电性结构显著不同,具有西低东高的特征,而郯庐断裂带则是两侧高低阻明显分界带;在南北方向,电性结构也存在较大不均匀性,嘉山地区呈现低阻特征,是断裂带上的电性分界点,郯庐断裂带在此处由北部的四条主断裂变成南部的两条.结合研究区地质、大地测量和地震学等资料,综合分析结果表明:郯庐断裂带作为苏鲁造山带和张八岭隆起高阻体陡立的西边界,切割深度超过莫霍面.嘉山地区相对低阻分割了张八岭高阻条带与苏鲁高阻体,阻碍了断层上应力的传递,造成了嘉山北、南两侧断裂带构造变形强、弱的变化,从电性结构上证实了郯庐断裂带具有分段性的特征;苏鲁高阻体南端向西偏转穿过郯庐断裂带,阻碍断层滑动,致使泗洪—嘉山段存在应力积累和断层闭锁的地震孕育环境,其地震危险性值得关注.

Based on the magnetotelluric(MT)array data covering Hefei-Suqian segment and its adjacent area of Tanlu fault zone(TLFZ),a reliable three-dimensional(3D)resistivity model of the survey area is obtained by using MT inversion technology and impression reconstruction method.In the electrical model,the electrical structure of the east and west sides of the TLFZ is significantly different,where the high-resistivity anomalies are distributed in shallow areas of both sides,and the deep electrical characteristics is low resistivity in the west and high resistivity in the east,while the TLFZ is a conspicuous boundary between high and low resistivity;In the north-south direction,the electrical structure has great heterogeneity as well.Jiashan area presents low resistivity,which is the North-South electrical boundary zone on the fault zone,where the TLFZ changes from four main faults in the north to two in the south.Combined with the data of geology,geodesy and seismology in the study area,the comprehensive analysis results show that the TLFZ,which is the steep western boundary of the Sulu Orogenic Belt and Zhangbaling Uplift,cut the Moho.The relatively low-resistivity anomaly in Jiashan area separates Zhangbaling high-resistivity belt and Sulu high-resistivity body,hinders the transmission of stress on the fault,and causes strong and weak structural deformation changes in the TLFZ on the north and south sides of Jiashan.It indicates that the TLFZ has characteristics of segmentation from the electrical structure.The south end of Sulu high-resistivity body deflects westward through TLFZ,hinders fault sliding,and makes Sihong-Jiashan segment has a seismogenic environment which could cause stress accumulation and fault locking.Earthquake risks caused by this shall be paid more attention.