关键词: 大地电磁测深, 视电阻率, 电性结构, 发震构造, 宁洱地震, 二维反演

Abstract: Magnetotelluric data have recently been obtained at 9 sites along a profile of about 8km long and orientated approximately E-W in the Ning'er earthquake area which lies in southwestern Yunnan province.From these data,the high-resolution apparent resistivity,impedance phase curves,skewnesses and regional strike were calculated by using the remote reference technique and robust data processing technique,and then analyzed.The 2-D inversion method NLCG was used for data interpretation.According to the 2-D electrical structure of Ning'er seismic area,there may be an extended fault because of an obvious different electrical structure between the left & right side of the site 12.On longitudinal distribution,the crust of this area can be divided into four electrical layers:1)Mesozoic and Cenozoic sediments,about 1km,2)Paleozoic sediment,about 5km,3)high conductive layers in crust,and 4)middle and lower crust.A high conductive layer exists in the crust of the area.Between the site 12 and 13,there might be a decollement structure on top of high conductive layer under them,because the buried depth of the layer is quite different between the left & right side of the site 12.Focal depth of the Ning'er earthquake is about 5km,the decollement structure presumed in this research lies in this layer,and its strike is NW,same as that of the major axis direction of the isoseismal curve of this earthquake.So we conclude that the decollement structure is the seismogenic structure.

Key words: magnetotelluric sounding, apparent resistivity, electrical structure, Ning'er earthquake, 2-D inversion