Spatio temporal seismicity variation in earthquakes of Uttaranchal region

The spatio temporal variations of seismicity preceding Uttarkashi, 1991 and Chamoli, 1999 earthquakes were studied based on the data during period 1981 to 2000 using catalogues prepared by India Meteorological Department. Two scenarios examined. In one case epicentral distance from respective impending worked out for all recorded a ten years prior earthquake Uttarkashi Chamoli respectively. other case, epicenter near latitude 30.2° N longitude 80.2° E Nepal border (where 1966 1980 occurred) considered compute distance. second was included because it is seismically active region where Dharachulla 1916 (magnitude 7.5) occurred. 1999, in Uttaranchal characterised six phases seismic activity namely (i) first quiescence or gap, (ii) swarm, (iii) (iv) foreshocks, (v) main shock (vi) aftershocks. Some differences among these could however, be noticed which explained through source mechanism, isoseismals, ‘b’ (Gutenberg Richter’s relationship), ‘h’ values (Omori’s law ) fractal dimension. It interesting point that occurrence swarms (second phase) pattern exhibits development gap (first after decay aftershock associated with previous large magnitude greater than equal M: 6.0 this region. We infer ‘gap’ (third characteristic complexity tectonics Uttaranchal. Thus, simple Kanamori’s asperity model modified consist complex tectonic zone Garhwal Himalaya. Detailed difference patterns dimensions estimated ‘b’values.