Magnetotelluric survey in the quest for crustal conductivities in Nepal after the Mw 7.9 Gorkha earthquake of April 25, 2015
Abstract
Magnetotelluric (MT) is a passive electromagnetic technique classically used in geophysical exploration for imaging electrical conductivity structures; especially in subduction zones, it has been proposed as a tool to approach rheology of the underground since the electrical conductivity is related with temperature, porosity, water content and minerals of rocks. First MT study of Nepal has been done based on 1996 and 1999-2000 campaigns by Lemonnier, Marquis and collaborators; the major result was the discovery of a conductive feature under the front of the Higher Himalaya coinciding with a zone of intense microseismic activity North of Kathmandu, and the position of a mid-crustal ramp along the major active thrust fault (Main Himalayan Thrust or MHT). The conductive feature discovered at the MHT is located in the area of the Mw 7.9 Gorkha earthquake of April 25, 2015. We consider a new MT campaign conducted in March 2016 in the area of the 1996 and 1999-2000 campaigns. The new data continue to exhibit MT response curves showing a decrease of the apparent resistivity at periods of 1-100s, that has been explained from the existence of a deep conductive structure at the MHT. Besides, we now use forward modeling with means of ModEM to discuss in more details the distortions and topography effects caused by the dip topography in the Himalayan area, especially at MT stations nearest to the MHT.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMGP34A..03S
- Keywords:
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- 0920 Gravity methods;
- EXPLORATION GEOPHYSICSDE: 0925 Magnetic and electrical methods;
- EXPLORATION GEOPHYSICSDE: 1219 Gravity anomalies and Earth structure;
- GEODESY AND GRAVITYDE: 1517 Magnetic anomalies: modeling and interpretation;
- GEOMAGNETISM AND PALEOMAGNETISM