Electrical structure of the Himalaya of central Nepal: High conductivity around the mid-crustal ramp along the MHT

Carole Lemonnier (1) , Guy Marquis (1) , Frédéric Perrier (2) , Jean-Philippe Avouac (2) , Gyani Chitrakar (3) , Basantha Kafle (3) , Som Sapkota (3) , Umesh Gautam (3) , Dilliram Tiwari (3) , Maksim Bano (1)

1 IPGS - Institut de physique du globe de Strasbourg
2 Laboratoire de Détection et de Géophysique
3 National Seismic Centre, Nepal

Twelve broadband magnetotelluric (MT) soundings were performed across the Himalaya of Central Nepal in 1996 in order to determine the electrical structure of the crust and its relation to geological structures and active tectonics. The MT impedance tensors were obtained for frequencies between 0.001 and 500 Hz. The 2-D section, derived from joint inversion of TE-and TM mode after RRI and Groom/Bailey decomposition, shows high conductivity in the foreland basin (-30 fl.m) that contrasts with the resistive Indian basement (> 300 oe;l.m) and Lesser Himalaya (> 1000 fl.m). In addition, our MT sounding reveals a major conductive feature beneath the front of the Higher Himalaya, also characterized by intense microseismic activity, and the position of a mid-crustal ramp along the major active thrust fault (MHT). This high conductivity zone probably reflects metamorphic fluids, released during underthrusting of the Indian basement and pervading well connected microcracks induced by interseismic stress build-up, or distributed brittle deformation around the ramp.

Domaines: Planète et Univers [physics]

Carole Lemonnier, Guy Marquis, Frédéric Perrier, Jean-Philippe Avouac, Gyani Chitrakar, et al.. Electrical structure of the Himalaya of central Nepal: High conductivity around the mid-crustal ramp along the MHT. Geophysical Research Letters, 1999, 26 (21), pp.3261-3264. ⟨10.1029/1999GL008363⟩. ⟨insu-01298173⟩