Abstract: Yuxi basin is one of the potential earthquake risk areas with high seismic frequency and intensity in Yunnan Province. In order to set up the "standard" structure model to be applied directly in earthquake prevention and disaster reduction,we used electrical resistivity tomography(ERT)to detect the electrical structure of mountain-basin transition zone in Yuxi basin and Pudu River Fault which is buried in and goes through the western margin under the support of the Special Project for the Fundamental R&D of Institute of Geophysics,China Earthquake Administration. In data acquisition,6 ERT measuring lines,as an important supplement to the seismic reflection survey,were designed to control the fault,and Wenner α arrays were used,with the electrode spacing of 6m,maximum depth factor of 30～75 and the electrode number of each array being 112～288.Our results indicate that Pudu River Fault in Yuxi basin consists of two NNE-striking branches,the east branch and the west branch. From south to north,the width of the fault zone becomes wider from Wenquan town to Heicun Village at first and then becomes narrower through Lianchi and Meiyuancun Village to Yukun Iron & Steel Co. Ltd. Its hanging wall is a low resistivity fracture zone,while its footwall appears as a homogeneous high-resistivity zone. The east branch (F_1-2) has an apparent dip direction of SE/S near and to the north of Meiyuancun Village and of NW near and to the south of Lianchi Primary School,with the apparent dip angle of 56°～73°,while the west branch(F_1-1) has an apparent dip direction of SE/E/S and the apparent dip angle of 38°～66°.The seismic results showed that both of the east and west branches of Pudu River Fault have the apparent dip direction of SE/E and apparent dip angle of 75°～80° in Yuxi basin(He et al., 2012),which are slightly different from our results.

Key words: Pudu River Fault, electrical resistivity tomography, electrical structure

摘要： 玉溪盆地是云南地区地震活动频度高、强度大的高潜在危险区之一。为了建立直接服务于该区域防震减灾的 "标准"结构模型,利用电阻率层析成像技术探测了玉溪盆地盆山过渡带的电性结构以及隐伏并穿过玉溪盆地西缘的普渡河断裂。在数据采集中,作为地震浅层反射勘探的重要补充,共布设了6条电阻率层析成像测线来控制该断裂。使用的观测装置为Wenner α,电极间距为6m,最大隔离系数为30～75,每个排列的电极数目为112～288个。探测结果表明,玉溪盆地内的普渡河断裂分为NNE走向的东西两支; 断裂带的宽度由南向北先从温泉镇到黑村附近逐渐变宽,经莲池小学、梅园村到玉昆钢厂附近后逐渐变窄; 断裂的上盘为低阻破碎带,下盘为较均匀的高阻结构。东支(F_1-2)的视倾向在梅园村及以北为SE/S,在莲池小学及以南为NW,视倾角为56°～73°;西支(F_1-1)的视倾向为SE/E/S,视倾角为38°～66°。地震勘探结果认为普渡河断裂的东西两支的倾向在整个玉溪盆地内均为SE/E,视倾角为75°～80°,这与我们的结果略有差异。

关键词: 普渡河断裂, 电阻率层析成像, 电性结构