Intra-Crustal Seismicity Triggering in Shillong Massif – An Appraisal on Recent Seismicity

Shillong plateau in the North East India resembles a kind of inselberg, confined in between the great Hilamalayan mountain belts in the north and the Arakan-Yoma towards east. The study area is governed by a system of complex seismotectonic features responsible for the intense seismicity in the region, significantly the devastation aftermath the 1897 great Assam Earthquake (Ms~8.7). Spatio-temporal distribution of seismicity triggering inside the plateau from 1966 to 2013 suggests distinctly variable depth-ranges of seismicity zones within the crust. The depth section counterparts of the seismicity monitoring within Shillong plateau and its periphery infers the bottom of the seismogenic zone to lie at ~40km depth with an average depth of earthquake occurrence at 22.31km; besides, the study also dictates the dominant earthquake magnitude as ≤4.99Mw, wherein most of the earthquakes are confined within magnitude 3-5 Mw with an average magnitude 3.42 MW. The study reveals intense seismic activity in the central and western part of Shillong plateau owing to the conjecture of a number of active faults. The present study incorporates both qualitative as well as quantitative approach while understanding the types of recent seismicity pattern in the Shillong massif.