Estimation of Source Parameters of Local Earthquakes Originated in Shillong-Mikir Plateau and its Adjoining Region of Northeastern India

We estimate the source parameters (seismic moment, source radius, stress drop, and source displacement) and scaling laws for local earthquakes that occurred in the Shillong-Mikir plateau, Assam Valley, and Arunachal Himalaya in northeast India during 2001-2008. The source parameters were determined using the spectral analysis of P waves from the vertical component seismograms, after correction for attenuation. Seismic moments are observed within the range from 9.51 x 10(12) to 2.74 x 10(15) N.m; stress drop ranges from 4 x 10(5) to 9 x 10(7) Pa for the Brune model and 7 x 10(5) to 1 x 10(8) Pa for the Madariaga model. Seismic events in this study are prominent with an average stress drop of 0.1-10 MPa. The effect of site geology may be a contributing factor for such a variation in stress drop. Source dimensions are, however, found to be smaller within the major part of the plateau. It is suggested that local earthquakes in the region are associated with a brittle shear-failure mechanism on fault segments and/or the presence of weakened zones, and earthquakes are triggered by low deviatoric stress. Empirical relations between M-w-M-L and M-0-M-L are developed leading to the future prediction of calibration coefficients for the local earthquakes in the Shillong-Mikir plateau and its adjoining region.