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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
JSS014 Oral Presentation 2253
Seismic image of the Central Himalaya (India) from broadband seismic
network
Mr. Ashish Kr.
Seismic Tomography Group National Geophysical Research Institute IASPEI
K. Sivaram, P. Rajgopala Sarma, K. Suryaprakasam, S. S. Rai
We investigate the variation in crustal S-wave velocity structure, 3-D distribution of seismic cloud and
the nature of mantle layering from the exposed Indian shield (Aravalli craton ) in south to the southern
Tibetan Detachment (STD) in the Kumaon- Garhwal segment of the central Himalaya using a network of
25 broadband seismographs operating in the region since April 2005. The seismic network comprising of
Guralp CMG-3T (120 s) seismometer and REFTEK data logger record the seismic waveform in
continuous mode at 50s/s. The stations were aligned NE- SW direction almost perpendicular to the
strike of the Himalaya. The stations were closely spaced at ~7-10 km interval from the Himalayan
Frontal Thrust (HFT) in south to the STD in north and are widely spaced in Gangetic plain and Aravalli
craton. We analysed over 100 teleseismic and 600 local earthquakes recorded by the network during
April 2005- Oct 2006 to generate velocity model and the seismicity pattern. The 1-D shear velocity
structure model at individual station is created through joint inversion of receiver functions from
different azimuths with the surface wave group velocity measurements. Some of the important results
include: 1.Northern Indian shield (Aravalli craton) characterized by a ~38 km thick crust with a
comparatively lower velocity (3.6 km/s. 2.Dip of the Indian Moho is 6-8 deg. beneath the lesser
Himalaya with the average Pn and Sn velocity of 8.2 and 4.7 km/s, derived from the travel times of
updip and downdip refracted waves. 3.Receiver function modeling results clearly map the Main
Himalayan Thrust and also the Indian Moho, both showing significant change in their dip to the north of
MCT. This is also supported by the seismic trend. 4.Presence of low velocity in the depth 20-30 km in
the region between MCT and STD is modeled from receiver function time series. 5.Uplifted 410
discontinuity while the 660 km discontinuity split into 660 and 710km depths. 6.Seismicity is prevalent in
the lower crust while it is nearly absent in the uppermost mantle.
Keywords: himalaya, crust structure, receivar function