Source characteristics of the NW Himalaya and its adjoining region: Geodynamical implications

Abstract

In this study, we propose a novel interpretation of source parameters estimated using Brune model for the NW Himalaya and its adjoining region. Analysis of 157 events (2.2 ≤ Mw ≤ 4.9) resulted in the scaling relationship between seismic moment (M0) and corner frequency (fc) for the region as: M0 = 8 × 1022 fc−2.89, which is in good unison to the Garhwal and the Kumaon Himalaya with analogous seismogenic potential. Variability of Kappa (0.01 s - 0.08 s) with varying number of events (2.5 ≤ M ≤ 5.0) at different depths is indicative of nature and extent of structural heterogeneity beneath the source zone, which controls the propensity of background seismicity that provides enough testimony to complex geodynamical set-up of the NW Himalaya and its adjoining region.Source radii of source zone varying from 148 m to 975 m with static stress drops calculated for a given constant stress of 0.1 bar, 1 bar, 10 bar and 100 bar correspond to an average stress drop varied from 0.4 bar to 99.9 bar. Seismic moments of events vary from 2.64 × 1019 dyne-cm to 2.32 × 1023 dyne-cm with increase of the source radii. We infer that variability in stress drop (Δσ) for seismic moment (Mo) is attributed to different seismic sources of varying strengths associated with different structural heterogeneities. Stress drop (Δσ) of the events has good correspondence with source depth, having the linear relationship of shear stress regime in the brittle crust with stress drop (Δσ) and source depth, suggesting the presence of intricate subsurface seismogenic sources beneath the NW Himalaya and its adjoining region.