STUDY OF SOURCE PARAMETERS OF LOCAL EARTHQUAKES IN THE GARHWAL AND KUMAUN HIMALAYA

Abstract

Earthquake source parameters provide great deal of information about the characteristics of earthquake source. Parameters such as stress drop, corner frequency, and fm, have applications in the estimation of strong ground motion. In the present study source parameters of more than 100 local events (0.1<M3.5), have been estimated from the available digital time histories and using Brune model. Epicenters of majority of events are distributed along the trace of MCT between Barkot and Chamoli. Few events occurred in the Higher Himalaya to the northwest of Barkot and also in the Sub Himalaya. Seismic moments, Source radii, and Stress drops span the range from 3.03 x 1017 dyne-cm to 2.75 x 1021 dyne-cm, 111.7 m to 314.4 m, and 0.01 bars to 40 bars respectively. Maximum observed stress drops are associated with the events located at a distance of about 25 km in the west of epicenter of the Chamoli earthquake. Events with stress drops between 5 bar and 40 bars occurs at a depth of about 15 km. Stress drop increases with seismic moment for events with seismic moments above 1 x 1019 dyne-cm, and follows the relation: A6 (bars) = 6E-'6 M00'8. A scaling law M. f C3 =5.0 x 1013 N-m/sec3 between seismic moment and corner frequency (1.0<MW<3.3) has been developed for the region. Almost similar trend between f and fm with seismic moment has been observed and f and fm follow the empirical relation: fma,, = 3f -2.6 for the region. Consistency in the f0 and fmax which decreases with seismic moment has confirmed the stochastic nature of high frequency ground motion in the Garhwal and Kumaun Himalaya.