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Instituto de Geofisica UNAM, CU, 04510 Mexico, DF Mexico
Indian Meteorological Department, Lodhi Road, New Delhi 110003, India
National Geophysical Research Institute, Hyderabad 500007, India
Department of Science and Technology, New Mehrauli Rd, New Delhi 110016, India
Abstract
In the past two years, a permanent network of 10 broadband seismographs has become operational in the Indian Peninsular shield region. In this article, we analyze the data recorded by this network with two goals: (1) to lay ground for a quick estimation of source parameters of future earthquakes in the region and (2) to estimate the source parameters of the destructive Jabalpur earthquake of 21 May 1997 (Mw = 5.8), which occurred within the network. Toward these goals, we measure Rayleigh- and Love-wave group velocity dispersion curves in the period range of 10 to 75 sec and invert these curves to estimate the crustal and the upper mantle structure below the Indian shield region. Our best model consists of a two-layer crust; the upper layer is 14-km thick with a shear-wave velocity (Vs) of 3.55 km/sec; the corresponding values for the lower layer are 25 km and 3.85 km/sec. Vs for the upper mantle is 4.65 km/sec. Based on this structure, we perform a moment tensor (MT) inversion of the bandpassed (0.05-0.02 Hz) seismograms of the Jabalpur earthquake. The best fit is obtained for a source located at a depth of 42 km, with a seismic moment, M0, of 7.7 x 1024 dyne cm, and a focal mechanism with strike 61°, dip 64°, and rake 74°. These source parameters are similar to those previously reported in the literature, demonstrating that a routine MT inversion of moderate and large Indian Penisular earthquakes is now possible. A careful examination of the seismograms and modeling of the two closest records reveal that the Jabalpur earthquake nucleated in the lower crust at a depth of 
36 km. It consisted of two subevents separated in time by 0.65 sec, with the second subevent located 2 km above the first one. The total source duration was 1.4 sec.
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