Source Parameters and Scaling Relation for Local Earthquakes in the Garhwal and Kumaun Himalaya, India

Abstract

Earthquake source parameters provide great deal of information about the characteristics of earthquake source. Parameters such as stress drop, corner frequency, and f_max have applications in the estimation of strong ground motion. In the present study source parameters of 107 local events (0.1≤M_L≤3.5), have been estimated using software EQK_SRC_PARA. 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: Δσ (bars) = 6x10^-16 M₀^0.8. A scaling law M₀f_c^2.7 =5.0 x 10¹³ N-m/sec^2.7 between seismic moment and corner frequency (1.0<M_w<3.3) has been developed for the region. Almost similar trend between f_c and f_max with seismic moment has been observed and f_c and f_max follow the empirical relation: f_max = 3 f_c -2.6 for the region. Consistency in the f_c and f_max which decreases with seismic moment has confirmed the stochastic nature of high frequency ground motion in the Garhwal and Kumaun Himalaya.