Moment Magnitude (M _W) and Local Magnitude (M _L) Relationship for Earthquakes in Northeast India

摘要

An attempt has been made to examine an empirical relationship between moment magnitude (M _W) and local magnitude (M _L) for the earthquakes in the northeast Indian region. Some 364 earthquakes that were recorded during 1950-2009 are used in this study. Focal mechanism solutions of these earthquakes include 189 Harvard-CMT solutions (M _W ≥ 4. 0) for the period 1976-2009, 61 published solutions and 114 solutions obtained for the local earthquakes (2. 0 ≤ M _L ≤ 5. 0) recorded by a 27-station permanent broadband network during 2001-2009 in the region. The M _W-M _L relationships in seven selected zones of the region are determined by linear regression analysis. A significant variation in the M _W-M _L relationship and its zone specific dependence are reported here. It is found that M _W is equivalent to M _L with an average uncertainty of about 0. 13 magnitude units. A single relationship is, however, not adequate to scale the entire northeast Indian region because of heterogeneous geologic and geotectonic environments where earthquakes occur due to collisions, subduction and complex intra-plate tectonics.