On the occurrence of small and moderate earthquakes of the Himalayan Seismic Belt

Abstract

Small and moderate magnitude earthquakes occur along a narrow belt in the Himalaya. The belt of these earthquakes, referred to as the Himalayan Seismic Belt (HSB), lies close to the surface trace of the Main Central Thrust (MCT). It coincides with the topographic front between the Lesser and Higher Himalaya, the zone of increased gradient of the Himalayan rivers, high interseismic elevation change rates deduced from repeat levelling measurements, and the high conductive feature beneath the southern Higher Himalaya. The hypocentres of these earthquakes mark the inferred downdip edge of the main thrust zone (MTZ). In this article, we suggest that the earthquakes of the HSB occur as a result of strain accumulation on the MTZ. Our simple calculations of change in static stress due to strain accumulation on the MTZ suggest that the static stress increases on the gentle planes above and close to the downdip edge of the MTZ, facilitating the occurrence of these earthquakes.