IDENTIFICATION OF POTENTIAL AREAS FOR THE OCCURRENCE OF STRONG EARTHQUAKES IN HIMALAYAN ARC REGION

Morphostructural zoning (MSZ) scheme of the Himalayan are region as obtained from a joint study of topographic, geological and tectonic maps as well as satellite imagery is analysed. Three types of morphostructures have been determined: territorial units (blocks of different ranks), linear zones limiting these blocks (lineaments) and intersections of the lineaments (knots). Comparison of MSZ scheme with the known seismicity indicates epicenters of strong earthquakes (M greater-than-or-equal-to 6.5) clustered around some of these knots. Pattern recognition method is used to determine seismically potential areas for the occurrence of strong earthquakes of magnitude greater-than-or-equal-to M(o). We have carried out two such studies for the Himalayan arc region, one for M(o) = 6.5 and the other for M(o) = 7.0. Out of a total number of 97 knots, 48 knots are found to be seismically potential for the occurrence of earthquake of M greater-than-or-equal-to 6.5. The results of the study for M(b) = 6.5 were presented in the symposium on ''Earthquake Prediction'' held in Strasbourg, France, March 1991 (Gorshkov et al 1991). The epicenter of Uttarkashi earthquake of magnitude, M(b) = 6.6 that occurred in the late hours of 19th October 1991 (UTC) lies in the vicinity of one such knot. The second study carried out subsequently shows that only 36 knots are potential for the occurrence of earthquakes of M greater-than-or-equal-to 7.0, which include the knot associated with the Uttarkashi earthquake.