Widespread earth tremors in parts of Central Tamil Nadu on 12th August 2011 and its significance

The southern part of the Indian Peninsular has started witnessing fast recurring seismicities and earth tremors with the magnitude of 3–5 in the recent years. In this context, the earthquake occurred, with a magnitude of 3.5, east of Ariyalur, Central Tamil Nadu, on 12^th August, 2011 is significant. It is because, followed by the earthquake, tremors were felt in over 35–40 villages in an area of 8000 sq km along with the development of cracks and dislocations in buildings in several places. The remote sensing observations showed that while the Ariyalur epicenter is in the eastern Tertiary formations, the tremor felt villages lie in the western crystalline formations. Again the correlation of remote sensing based lineaments with Ariyalur earthquake, the related tremors and also a few past seismic events of the area showed that these epicenters mostly lie along NE-SW lineaments. The tremors related to Ariyalur event were also felt mostly in villages located again in the vicinity of NE-SW lineaments. The lineaments appear to be post collision tectonic grains related to the still on going northerly compressive force due to which only the Indian plate is buckling and fracturing now. Hence the 12^th August, 2011 seismic event of Ariyalur cannot be taken as an isolated phenomenon and appears to be related to the Indian plate deformation as a whole. So it calls for in depth studies in the context of fast relapsing seismicities in peninsular India.