HR: 10:55h
AN: T52A-03    [Abstracts]
TI: Geometry and Characteristics of the Main Himalayan Thrust in Nepal/Tibet Revealed by the Hi-CLIMB Seismological Experiment
AU: * vergne, j
EM: vergne@geologie.ens.fr
AF: Laboratoire de Géologie, Ecole Normale Supérieure, 24 rue lhomond, Paris, 75231 France
AU: Nábělek, J L
EM: nabelek@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331 United States
AB: The Main Himalayan Thrust (MHT) is considered to be the main, indeed unique, interface separating the subducting India plate and the hanging wall constituted by the Himalayan wedge and the Tibetan plateau. However, little is known about the geometry and the characteristics of this large detachment, especially in Nepal where rupture on the MHT is known to have produced historical M>8 earthquakes. Here we make use of the high density (~ 3 km spacing) of the seismological stations installed in Central Nepal in the framework of the Hi-CLIMB project, to produce the first image of the MHT in this region. We converted thousands of high quality records of distant earthquakes into high frequency receiver functions and migrated them to enhance major upper-crustal discontinuities. We also produced a local tomography of the Rayleigh group velocities by correlating noise signal between pairs of stations in Nepal. Both methods reveal a thin, almost horizontal low velocity layer at around 12 km depth under the main Hi-CLIMB profile in Nepal, with an abrupt upper boundary that probably marks the trace of the MHT in this region. Further north, another thin dipping low velocity zone is observed and its location fits well with the previously imaged MHT under the Himalayas. These local decreases of seismic velocity associated to the MHT are interpreted in term of presence of fluids: aqueous fluids trapped under the seismogenic part of the MHT in Nepal and partial melt in its creeping part under the Himalayas.
DE: 1236 Rheology of the lithosphere and mantle (7218, 8160)
DE: 7200 SEISMOLOGY
DE: 8045 Role of fluids
DE: 8108 Continental tectonics: compressional
SC: Tectonophysics [T]
MN: Fall Meeting 2005