Northeast India region is one of the most seismically active areas in the world. Events data for the period 1897–2010, used in this study has been largely compiled from global ISC, NEIC and GCMT databases. Historical seismicity catalogue of Gupta et al (1986) and some events data from the bulletins of India Meteorological Department are also used. Orthogonal regression relations for conversion of body and surface wave magnitudes to 𝑀_w,HRVD based on events data for the period 1978–2006 have been derived. An Orthogonal Standard Regression (OSR) relationship has also been obtained for scaling of intensity estimates to 𝑀_{w,NEIC} using 126 global intensity events with intensity VI or greater during the period 1975–2010.

Magnitude of completeness and Gutenberg–Richter (GR) recurrence parameter values have been determined for the declustered homogenized catalogue pertaining to four different time periods namely, 1897–1963, 1964–1990, 1964–2000 and 1964–2010. The $M_c$ and ‘𝑏’ values are observed to decrease and increase, respectively, with addition of newer data with time. The study region has been subdivided into nine seismogenic zones keeping in view the spatial variations in earthquake occurrence and prevalent tectonics. $M_c$, ‘𝑏’ and ‘𝑎’ values have been estimated with respect to each zone, and the variations in the values of these parameters have been analysed.