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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS011 Oral Presentation 2097
Crust and mantle structure from the Northern Indian Shield to Western
Himalaya and Ladakh using receiver functions
Dr. Shyam Rai
Seismic Tomography National Geophysical Research Institute IASPEI
K. Suryaprakasam, Keith Priestley, Vinod Gaur
We analysed over 2000 P-S converted receiver functions from 24 broadband seismograph locations from
the northern edge of the Indian shield to the western Himalaya and Ladakh- Karakoram to model the
structure of the crust and the underlying mantle transition zone. Crustal structure is imaged through
joint inversion of the receiver functions with the surface wave group velocity measurements while the
mantle transition zone discontinuities are mapped through the common depth point stacking of the
mantle converted receiver functions. The Moho depth beneath northern India is ~38 km that
progressively deepens to ~55 km beneath Higher Himalaya and ~75 km beneath the Ladakh and
Karakoram. Upper crust beneath northern India is more felsic (Vs 3.6 km/s. Unlike the central Tibet and
Nepal, the crust beneath western Himalaya, Indus suture and Ladakh does not contain signature of low
velocity. In the mantle transition zone (MTZ), beneath the Gangetic plain we mapped the 410 km
discontinuity at ~392 km depth while the discontinuity at the base of the transition zone splits into 660
and 715 km with the MTZ thickness ~ 260 km. These observations support the presence of high velocity
slab beneath the Gangetic plain and Himalaya whose interaction with the upper mantle was responsible
for the observed complexity of 660 km discontinuity possibly due to phase transformation from garnet
to perovskite. We interpret this as the signature of fossil slab broken off the subducting Indian margin
or the Tethys. In contrast, beneath Ladakh 410 is at its normal depth and the average MTZ thickness is
242 km suggesting distinct thermal state of mantle between Himalaya and Ladakh.
Keywords: western himalaya, receiver function, crust mantle