Evaluation of Crustal and Upper Mantle Structures Using Receiver Function Analysis: ISM Broadband Observatory Data

A three-component broadband seismograph is in operation since January 2007 at the Indian School of Mines (ISM) campus, Dhanbad. We have used the broadband (BB) seismograms of 17 teleseismic events (M ≥ 5.8) recorded by this single BB station during 2008-09 to estimate the crust and upper mantle discontinuities in Dhanbad area which falls in the peninsular India shield. The converted wave technique and the Receiver function analysis are used. A 1-D velocity model has been derived using inversion. The Mohorovicic (Moho) discontinuity (crustal thickness) below the ISM observatory is estimated to be ~41 km, with an average Poisson ratio of ~0.28, suggesting that the crust below the Dhanbad area is intermediate to mafic in nature. The single station BB data shed new light to the estimate of crustal thickness beneath the eastern India shield area, which was hitherto elusive. Further, it is observed that the global upper mantle discontinuity at 410 km is delayed by ~0.6 sec compared to the IASP-91 global model; this may be explained by a slower/hotter upper mantle; while the 660 km discontinuity is within the noise level of data.