Seismic hazard estimation and medium-term earthquake precursor analysis of North East India: an assessment on large earthquake scenario

The North-Eastern region of India has the distinction of being one of the most seismically active and tectonically complex regions in the world. The region has periodically jolted by a number of large earthquakes. The temporal and spatial frequency-magnitude distribution (FMD) of earthquakes in three major selected regions of North-East India, namely Shillong-Mikir Hills, Arunachal Himalaya, and Assam Foredeep region, are examined in this study. Temporal variation of ‘b’ shows a significant declination prior to a large earthquake, which strongly advocates for a medium-term (months-year) earthquake precursor. Similarly, spatial distribution map is prepared by estimating b-value at every ${0.01}^o\times {0.01}^o$ grid using the nearest 150 events, which is vital in understanding the stress regime of a specific region. The present study critically demonstrates the higher b-value regions associated with minimum seismicity and vice-versa, especially focusing on large earthquake scenario. High anomalies of ‘b’ were found in the regions of Shillong-Mikir hills and Arunachal Himalaya, whereas the Assam-Foredeep region, free from seismic activity for a long period, shows a low. It may be due to the accumulation of stress energy within the region for a long time and could be an alarming sign for future large events.