Seismic evidence of pop-up tectonics beneath the Shillong Plateau area of Northeast India

Abstract

Our detailed 3-D seismic tomographic assimilation using high-quality phase arrival time data recorded by the local seismographic network demonstrated that heterogeneities in the crustal faults have contributed significantly to the pop-up tectonics beneath the Shillong Plateau, characterized by high-V and low-σ. The major seismogenic faults, namely, the north-dipping Dapsi thrust in association with Dauki fault in the south and south dipping Brahmaputra fault in the north, located either side of the Shillong Plateau that acted as the causative factors for the pop-up, which attributed to the lithostatic (high-V, low-σ) and sedimentary (low-V, high-σ) load, respectively. Seismicity is found confined to a depth ≤ 60 km. Uneven distribution of structural heterogeneities in the upper crust is responsible for earthquake genesis of varying strengths. It is intriguing to note that high-velocity anomalies and low-ϭ in the uppermost crust, interpreted as the Shillong Plateau that acted as a geometric asperity and the juxtaposition of high-V and low-V became the source zone of the 1897 Shillong earthquake (Ms 8.7) as a novel observation for the region. Structural heterogeneities are distinctly distributed between low-V, high-σ and high-V, low-σ in the lower crust plays a major role for future intense seismogenesis due to differential strain accumulation.