Magnetotelluric evidence of fluid-related seismicity beneath the Chuxiong Basin, SE Tibetan Plateau

Abstract

Fluids play an important role in intracontinental seismicity and have become an important issue in solid earth sciences. In this study, we present evidence of fluid-related seismicity on the southeastern Tibetan Plateau. A sequence of large earthquakes (Ms > 6.0) occurred in the Dayao and Yao'an areas within the Chuxiong Basin from 2000 to 2009, where no obvious traces of active faults at the surface indicate the source fault of these earthquakes. To reveal the deep earthquake structure and the mechanism of these earthquakes, we carried out two magnetotelluric (MT) profiles that intersected in the epicentral region. The three-dimensional (3-D) inversion method was used to provide a more realistic electrical resistivity model since phase tensor analysis showed 3-D features. The electrical structures along the two profiles showed similar characteristics: lower crustal conductors underlie the upper crustal resistive zone, the resistive zone may correspond to a crystalline basement, and the lower crustal conductors were interpreted as aqueous fluid-related and water-derived partial melting. Earthquakes were distributed mainly in the upper crustal resistive zone but not in the underlying conductive zones, which indicated that fluid migration into the upper crust may have contributed to triggering earthquakes in this area.