IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS011 Poster presentation 2171
Crustal and upper mantle structure beneath the Deccan Volcanic Province
of India
Dr. Mohan Gollapally
Earth Sciences Indian Institute of Technology Bombay
Pankaj Kr. Tiwari
An experiment was launched during 1999-2006 to map the crustal and upper mantle discontinuities
beneath the Deccan Volcanic Province (DVP) through deployment of broadband seismographs in phases
at thirteen sites along a 600 km long profile in western India. The Receiver function analysis using
about 1200 teleseismic events enabled imaging the Moho and the mantle discontinuities beneath DVP
and the adjoining regions. The crustal thicknesses are estimated to range between 33 and 38 km
averaging 36 2 km at all stations in DVP suggesting a normal crust. The P-to-s conversion times from
the 410 and 660 km discontinuities beneath DVP are normal, as per IASP91 model. In comparison, the
P410s and P660s from the mantle discontinuities beneath the Cambay rift and the Gulf of Cambay are
delayed by 0.5 to 1s respectively with respect to the IASP91 model. The delays suggest presence of
zones of low velocities (LVZs) in the upper mantle, coinciding with the low velocity track presumably
representing the Deccan plume track starting from north Cambay. However, the LVZs are dominant only
in the Gulf of Cambay and appear to extend north into the Cambay rift with diminished magnitude
contrary to that expected for a plume track. Contrasting upper mantle images beneath DVP and the
adjoining offshore region suggests the absence of anomalous thermal or compositional anomalies in the
upper mantle beneath DVP, south of the Narmada rift, while possible rift related signatures in terms of
LVZs are preserved beneath the Gulf of Cambay.
Keywords: deccan volcanic province, mantle discontinuities, receiver function