Northeast India is one of the world’s most seismically active regions. The event data included in this research for the period 1737–2012 is mostly obtained from worldwide database agencies such as ISC, NEIC, and GCMT. Historical seismicity is collected from published and unpublished documents and some earthquake events are collected from the Indian Meteorological Department Bulletins. As the M_w scale is developed and validated in the southern California region and overestimates the smaller magnitude earthquakes, therefore, recent literature suggested an improved version of the seismic moment magnitude scale (M_wg) applicable for the entire globe considering both long- and short-period frequency-spectra using modern instrumental data. To update the earthquake catalog of Northeast India, we prepared empirical relationships between different magnitudes to M_wg using robust statistical General Orthogonal Regression. A procedure is also suggested for converting different earthquake sizes towards seismic moment scale. The Magnitude of Completeness (M_c) and the Gutenberg–Richter (GR) recurrence parameter values for the declustered homogenized catalog in four time periods, namely 1737–1963, 1964–1990, 1964–2000, and 1964–2012, have been computed. Our analysis suggests that the use of the M_wg scale improves seismicity parameters ‘b’ up to 30%, ‘a’ up to 17%, and ‘M_c’ up to 18% for the Northeast India region. A complete unified earthquake catalog in terms of advanced seismic moment magnitude scale could help understand seismicity and earthquake engineering studies of the region.

This study uses the Das magnitude scale (M_wg) to improve probabilistic seismic hazard assessment (PSHA) in Northeast India, where traditional M scales introduce inaccuracies for events below M 7.5. The M scale is mathematically flawed in this range, being based on an equation derived for Ms ≲ 7.0—an inconsistency evident in the observed data. Using a unified earthquake catalog of 9,968 events, calibrated to M_wg, in conjunction with region-specific seismogenic zones and observed-data-validated ground motion models, hazard spectra were derived for 475- and 2475-year return periods. The resulting PSHA indicates maximum peak ground accelerations (PGA) of 0.908 g and 1.5405 g for 10% and 2% exceedance probabilities over 50 years, respectively. Comparative analysis revealed significant discrepancies between M and M_wg, with M overestimating ground motion by up to 40% for the 475-year return period and 20% for The 2475-year return period, particularly in regions prone to medium-range earthquakes. This overestimation of the M scale (mainly for smaller and medium earthquakes) was previously reported by Choy and Boatwright in 1995 using the Gutenberg–Richter energy equation. This issue can be effectively addressed by adopting the M_wg scale, which provides a more accurate representation of seismic energy. Furthermore, M scale underestimated PGA by up to 10% for very large magnitude events. These discrepancies, particularly overestimation in smaller and medium earthquake ranges, have critical implications for structural design. The adoption of M_wg provides a more accurate seismic hazard representation, necessitating a reevaluation of current building codes and emergency response protocols in Northeast India.