The 24 August 2021 Mw 5.1 earthquake, 320 km northeast of Chennai, India: brittle rupture of a fault line

Abstract

On 24 August 2021 at 12:35:50 IST, an undersea earthquake of magnitude Mw 5.1 on the Richter scale occurred at a depth of around 10 km and shook some parts of the southeast coast of India (source: USGS). The epicentre of the quake lay in the Bay of Bengal (BoB) at 14.440°N lat. and 82.991°E long., about 296 km southeast of Kakinada, Andhra Pradesh and 320 km northeast of Chennai (Figure 1). A few coastal parts of Tamil Nadu and Andhra Pradesh felt mild tremors, but there was noreported destruction, tsunami warning and aftershocks. Although the eastern BoB has witnessed a few earthquakes in the historical past (see figure 1 of Krishna et al.1), the western BoB has remained relatively stable. The last activity was noticed more than a century ago on 19 May 1918 at a location of 15.9°N, 83.7°E (Figure 1). Inthe recent past, on 21 May 2014, the eastern BoB had witnessed a 6.0 magnitude earthquake at 18.3°N, 87.9°E. These quakes are situated in the far interior away from active seismic zones such as divergent/convergent/transform plate boundaries, and also from diffusive plate boundary in the Indian Ocean. Therefore, the present earthquake event has drawn our attention to examine available geophysical data around the earthquake location to discern possible causes that may have generated this unusual, shallow-depth earthquake