Depth-dependent seismic anomalies and potential asperity linked to fluid-driven crustal structure in Garhwal region, NW Himalaya

Abstract

Characterizing the stress heterogeneity and crustal complexities are essential to understand the important aspects of rupture development and its propagation in a tectonically active region. We analyze a continuous seismic data (1999–2020) to estimate stress drops, b-value, fractal dimension (Dc) and focal mechanisms using a local network of 14 broadband stations. Seismic periodicity on a Himalayan major thrust above locked zone, involves long period of stress accumulation and interseismic strain. There exist a good spatio-temporal-depth correlation between the estimated results which indicates the positive anomaly at 12–14 km (stress transition) beneath the Chamoli region. Interestingly, this region shows maximum geodetic strain rate with comparatively high-stress drop, low coefficient friction value and very low b- (0.583 ± 0.02) and Dc- (1.20 ± 0.01) values. Majority of moderate to strong earthquakes and swarms activity have occurred in this region with maximum crustal accommodation. It is also observed that the significant temporal decrease in b-value always followed by moderate earthquakes. Here shallow crustal potential seismogenic asperity controls the earthquake's stress drop and rupture propagation. The observed correlations strongly support the evidence of entrapped fluid-faults interaction which alters pore pressure and generates numerous ruptures. Also, the role of pressurized entrapped fluids and roughness of fault-plane responsible for low friction zone and microseismicity. Continuous stress accumulation along the fault-plane within the asperity could release significant amount of energy in future.