Moment magnitude – local magnitude relationship for the earthquakes of the Shillong-Mikir plateau, Northeastern India Region: a new perspective

Abstract

An attempt has been made to examine the empirical relationship between moment magnitude (M W) and local magnitude (M L) of earthquakes recorded in the Shillong-Mikir Plateau of Northeastern India. Moment tensor solutions of 106 earthquakes recorded during the period 1976–2009 are used. The focal mechanism solutions of these earthquakes include 1 Harvard-CMT solution (M W ≥ 4.0), 54 solutions from different publications and 51 solutions obtained for the local earthquakes (2.0 ≤ M L ≤ 5.0) recorded by a 20-station permanent broadband network during 2001–2009 in the region. The moment tensor solutions of these local earthquakes are obtained by the discrete wave number method. The M W –M L relationship in the region is determined by generalized orthogonal regression analysis, which is found to be M W = M L (1.00 ± 0.02) + (0.02 ± −0.05). It is observed that, on average, M W is equivalent to M L with an uncertainty of about (0.02 ± −0.05) magnitude units for earthquakes of the Shillong-Mikir Plateau. Conversion of M L to M W is recommended for seismic hazard analysis and tectonic studies in the region.