Structural Heterogeneity and Seismogenesis of the National Capital Region NCR-Delhi, India

Abstract

The local earthquake tomography technique has been applied to determine seismic velocities (Vp and Vs) and Poission’s ratio (ϭ) to unravel the connection between the variability of structural heterogeneities and seismogenesis with reference to seismotectonic of the National Capital Region (NCR) of India. This investigation analyzed about 6000 direct phase arrival data for crustal earthquakes recorded by 26 seismic stations ascribed to the National Seismological Network of India. We observed that the seismogenic structures are closely aligned with the sub-surface geological and tectonic patterns. Structural heterogeneities in high seismic velocities (Vp, Vs) and low Poisson’s ratio (ϭ) are associated with in-situ geological structures at depths < 30 km, where seismicity is concentrated conspicuously. This suggests that the competed rocks at shallow depths may be capable of seismogenesis in the area where most earthquakes occur. Specifically, ridges of the NCR inferred low Vp, Vs, and a high ϭ at deeper depths > 30 km, suggesting underneath geological formations associated with potentially fluid-filled rock matrix. In contrast, areas with several fault dispositions exhibited high Vp, Vs, and low ϭ, suggesting the competency for brittle failure. The seismic events are prevalent across various velocity zones but are much pronounced in areas with high ϭ, from which we infer that seismogenesis of the NCR-Delhi is dictated by weaker structural heterogeneities associated with fluid-filled rock matrix having interlinkages with past river microchannels containing fluids at depths where a majority of earthquakes occurred.