理塘断裂带南段强震空区的地壳三维电性结构及成因机制

研究强震活动带上的地震空区，是评估区域强震风险的重要方面。位于川滇地块内部的理塘断裂带，全新世以来发生过多次7级以上强震，但它的南段是明显的强震空区。目前因缺乏详细的地壳三维结构资料，给准确判断该区的强震危险性带来了困难。本课题拟在已有大地电磁数据基础上，新增52个宽频带大地电磁测点，以平均15km的点距覆盖理塘断裂带南段强震空区。采用多种大地电磁定性分析和两种三维反演方法，考虑压制局部畸变的影响，获得可靠的理塘断裂带南段地壳三维电性结构。结合地表构造与小震分布，研究理塘断裂带南段产状及向深部的延伸、变化情况；综合区域构造应力场、断层活动属性、地表形变特征，推断强震空区地壳变形样式；从电性结构出发，结合小震时-空演化规律，弄清断层带内是否存在局部高应变积累区；探讨强震空区形成的深部结构原因，并给出合理的动力学机制解释。研究结果将为评价该区强震风险性大小和认识地壳变形机制提供新的依据。

It is an important aspect to evaluate the risk of large earthquakes by studying the seismic gap in strong earthquake faults. The Litang faults are in the Chuandian block, on which several larger earthquakes had occurred with magnitudes over 7.0 since Holocene. The south segment of the Litang faults presents a significant seismic gap. However, because of the lack of three-dimensional crustal structure, it is difficult to better evaluate the risk of strong earthquakes in this seismic gap area. This proposed project intends to add 52 magnetotelluric stations with an average spacing of 15 km to cover the seismic gap in the south segment of Litang faults. To obtain a credible three-dimensional crustal resistivity structure, multiply MT quality analysis techniques, and two three-dimensional inversion methods will be applied. The distortion generated by the surface local anomalous body will under consideration. Combining with surface geological structure and relocated small earthquakes, the attitude of the south segment of Litang faults and its variations in geometry to the deep will be investigated. We will infer the crustal deformation pattern within the seismic gap, integrating the regional stress field, features of the active faults, and surface deformation pattern. According to the resistivity structure, the spatio-temporal evolution of the small earthquakes will be included to make clear whether there is a local high strain accumulation zone or not. We will discuss the cause from the deep structure to form this seismic gap and propose a reasonable geodynamic mechanism interpretation. These research results will provide new evidence for evaluating the risk of strong earthquakes and better understanding the region's crustal deformation.