Homogenization of Earthquake Catalog for Northeast India and Adjoining Region

A catalog for northeast India and the adjoining region for the period 1897–2009 with 4,497 earthquakes events is compiled for homogenization to moment magnitude M _w,GCMT in the magnitude range 3–8.7. Relations for conversion of m _b and M _s magnitudes to M _w,GCMT are derived using three different methods, namely, linear standard regression, inverted standard regression (ISR) and orthogonal standard regression (OSR), for different magnitude ranges based on events data for the catalog period 1976–2006. The OSR relations for M _s to M _w,GCMT conversion derived in this paper have significantly lower errors in regression parameters compared to the relations reported in other studies. Since the number of events with magnitude ≥7 for this region is scanty, we, therefore, considered whole India region to obtain the regression relationships between M _w,GCMT and M _s,ISC. A relationship between M _w,GCMT and M _w,NEIC is also obtained based on 17 events for the range 5.2 ≤ magnitude ≤ 6.6. A unified homogeneous catalog prepared using the conversion relations derived in this paper can serve as a reference catalog for seismic hazard assessment studies in northeast India and the adjoining region.