HR: 10:20h
AN: S31H-01    [PDF]
TI: The Geometry of Recently Digested India: First Results From HIMNT Receiver Functions Spanning the Collision Zone in Nepal and Tibet
AU: * Schulte-Pelkum, V
EM: vera_sp@cires.colorado.edu
AF: University of Colorado, 2200 Colorado Ave UCB 399, Boulder, CO 80309 United States
AU: Sheehan, A
EM: afs@cires.colorado.edu
AF: University of Colorado, 2200 Colorado Ave UCB 399, Boulder, CO 80309 United States
AU: Gibert, H
EM: hgilbert@geo.arizona.edu
AF: University of Colorado, 2200 Colorado Ave UCB 399, Boulder, CO 80309 United States
AU: Wu, F
EM: francis@binghamton.edu
AF: SUNY Binghamton, PO Box 6000, Binghamton, NY 13902 United States
AU: Aryal, R K
EM: nscdmg@mos.com.np
AF: Department of Mines and Geology, Lainchour, Kathmandu, 4119783 Nepal
AU: Bilham, R
EM: bilham@colorado.edu
AF: University of Colorado, 2200 Colorado Ave UCB 399, Boulder, CO 80309 United States
AB: Receiver functions from the first broadband seismic deployment to cover the plains of south Nepal, the Lesser and Greater Himalaya, and southern Tibet, reveal the base of the Indian continental crust to be descending gently from 45 km depth in the plains through a steeper ramp in the transition through the high ranges, to 70-80 km depth underneath the Tibetan Plateau. Our data from a network of 29 stations span 20 months and provide roughly 3000 high signal to noise 3-component teleseismic P-SV seismograms, allowing the construction of 3D images of the Himalayan crustal and mantle structure. Receiver functions at most stations exhibit strong back azimuthal variations, and we calculate common conversion point stacks to correctly locate P to S converters. We see a clear Moho descending from the south to the north. The crustal thickness in Tibet is consistent with results from INDEPTH studies to the east of our deployment area. At the transition from the Nepalese foothills to the high Himalaya, we observe a midcrustal conversion at an average of 20 km depth, which coincides with a zone of shallow earthquakes relocated using our stations (Monsalve et al., this meeting). We observe along-arc variations in the depth of the Moho and of midcrustal structures. It is possible that some of these midcrustal features are associated with regions of partial melt observed in the INDEPTH data. Our new seismic results allow us to constrain previous inferences from gravity and structural studies for a clearer picture of the mechanisms of the Himalayan collision.
DE: 7205 Continental crust (1242)
DE: 7218 Lithosphere and upper mantle
DE: 8102 Continental contractional orogenic belts
DE: 8122 Dynamics, gravity and tectonics
DE: 9320 Asia
SC: Seismology [S]
MN: 2003 Fall Meeting