Abstract:
The north eastern region of India is interwoven with numerous tectonic faults. The movement along these faults have resulted in high seismic activity as well as given rise to the Shillong Plateau (SP). The SP is surrounded by the Oldham, Kopili, Dauki and Dhubri faults. Each of these faults has generated earthquakes (EQs) in the past which have caused damages in the SP and surrounding areas. Present study aims at understanding the location and orientation of the faults surrounding the plateau. In order words, this study aims at characterizing the seismic sources located in the vicinity of the SP. Hence a seismotectonic province of 500km radius is developed for identifying and characterizing the potential seismic sources. The seismotectonic region is found to vary in terms of seismicity, tectonic features, geology, thickness of overburden, rupture characteristics, rate of movement. Hence, the seismotectonic region is divided into four seismic source zones namely; 1) the Shillong Plateau - Assam Valley Zone (SP-AVZ), 2) the Indo-Burma Ranges Zone (IBRZ), 3) the Bengal Basin Zone (BBZ) and 4) the Eastern Himalaya Zone (EHZ). EQ catalogues for each source zone is analyzed for completeness of magnitude and time. Seismic parameter ‘b’ estimated using maximum likelihood method are found as 0.91±0.03 0.94±0.02, 0.80±0.03 and 0.89 ± 0.03 for SP-AVZ, IBRZ, BBZ and EHZ respectively. The SP-AVZ shows relatively high recurrence rate for 1000 years period. Based on ‘b’ value and return period, SP-AVZ is found as zone of high hazard. The ‘b’ values are used to estimate the maximum potential magnitudes (Mp) generated by the identified faults.
