HR: 16:30h
AN: S22G-03    [PDF]
TI: Regional and Upper-Mantle Structure Model of Peninsular India and Relevance to High-Frequency Lg Seismograms
AU: * Saikia, C K
EM: chandan_saikia@urscorp.com
AF: URS Group, Inc., 566 El Dorado Street, Pasadena, CA 91101 United States
AB: The primary objective of this study is to develop regional and upper-mantle crustal structures of Peninsular India for estimating source parameters of smaller seismic events. To this end, we modeled regional seismograms generated by the May 21, 1997 Jabalpur earthquake in central India which occurred in the lower crust at a depth of 35 km. It was recorded at many teleseismic stations with usable signal-to-noise ratio, including several broadband regional stations in India. Teleseismic P waves were used to establish the complexity of the source process, focal mechanism and source depth of the earthquake by modeling amplitude and travel times of the pP and sP depth phases relative to the P wave onsets. Regional waveforms from this master event with known source parameters were used to develop corresponding Greens' functions for the paths to stations, namely Bhopal (BHPL), Bilaspur (BLSP) and Hyderabad (HYB). The complexity in teleseismic P and sP can also be observed in Pn and sPn with excellent compatibility. These same features can be identified in upper-mantle triplications at LSA ($\Delta$=$12\deg$), NIL ($Delta$=$12\deg$), CHTO ($\Delta$=$18\deg$), and AAK ($Delta$=$20\deg$) when modeled with existing shield models. The upper-mantle Pn phases (i.e., pP, sP, sPn, sSP, sPP, sPPPP etc.) can be positively identified in these observations and were found to be sensitive to the presence of gradient in the transition zones, especially beneath the 400 km discontinuity. The usefulness of these Green's functions is demonstrated by modeling the regional and sparse teleseismic data for a small earthquake (April 4, 1995) located near the Indian Nuclear Test Site at Pokhran. This study also establishes a regional waveguide for the path from the Pokhran Test Site to station Nilore (NIL) in Pakistan. We have also extended these regional models to have the capability of generating high-frequency Lg waves by introducing thin layers in the crust with alternating high and low-velocity distribution.
DE: 0689 Wave propagation (4275)
DE: 0935 Seismic methods (3025)
DE: 1020 Composition of the crust
SC: Seismology [S]
MN: 2003 Fall Meeting