Thenmala Fault System, Southern India: Implication to Neotectonics

Abstract

Abstract The Achankovil shear system is one of the major crustal scale structures in Peninsular India. This NW-SE trending shear zone stretches across the Western Ghats for a strike length of 120 km. A number of parallel lineaments demarcate this 15-20 km wide shear zone. Many studies were carried out to understand the origin and delineation of this structure. Low level seismicity reported in this region, however, does not suggest any relation with this shear zone and thus no significant study was carried out to understand its neotectonic behavior. However, there are a couple of faults identified in the southern end of this shear system viz., Thenmala and Thenmala south faults. Even though these faults were demarcated in hilly terrain of Western Ghats, its expression into the plain area east of the mountain terrain were not identified during the earlier studies. The present study however, delineated the signatures of these faults further in the southeast from satellite images. The traces of these faults are observed as multiple slip planes with varying deformation pattern. A group of N-S trending lineaments are also observed in hill ranges. Similarly, N-S trending long persistent vertical joints are observed in the plain area are free from displacement. The traces of NW-SE trending brittle faults observed in these areas crosscut all the joints including the N-S trending vertical ones. These observations suggest that the geomorphic signature associated with Thenmala lineaments may represent the youngest deformation (brittle) of the region.