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

Small and moderate magnitude earthquakes occur along a narrow belt in the H imalaya(1-4). The belt of these earthquakes, referred to as the Himalayan S eismic Belt (HSB), lies close to the surface trace of the Main Central Thru st (MCT)(1,4,5). If coincides with the topographic front between the Lesser and Higher Himalaya(1) the zone of increased gradient of the Himalayan riv ers(6), high interseismic elevation change rates deduced from repeat levell ing measurements and the high conductive feature beneath the southern Highe r Himalayan(12). The hypocentres of these earthquakes mark the inferred dow ndip edge of the main thrust zone (MTZ)(5,8,10,11). In this article, we sug gest that the earthquakes of the HSB occur as a result of strain accumulati on on the MTZ. Our simple calculations due to strain accumulations of chang e in static stress on the MTZ suggest that the static stress increases on t he gentle planes above and close to the downdip edge of the MTZ, facilitati ng the occurrence of these earthquakes.