Geomorphic Indicators of Neotectonism from the Precambrian Terrain of Peninsular India: A Study from the Bharathapuzha Basin, Kerala

Peninsular India is considered tectonically stable even though a few damaging earthquakes occurred here. Most of the causative faults are detected only after the occurrence of the earthquakes. The present study is an attempt to demarcate such active structures, from the Precambrian crystalline terrain of Peninsular India, through remote sensing, geomorphic analysis and field verification. The study area falls in the vicinity of Palghat Gap, a prominent physiographic break in the Western Ghats, where a low level seismicity is reported since 1989. Our study identified a WNW-ESE regional structure, which has influenced the drainage network of the area. The right angled turn of Bharathapuzha River at Desamangalam near this structure shows the influence of the structure to the drainage system. This structure is also characterized by the presence of a waterfall and a brittle fault dated neotectonic activity. The drainage basins lying south of this structure show anomalous values of asymmetry factors (>65 or <35). The Transverse Topographic symmetry factors also show anomalous pattern on either end of this structure and display a consistent shift in drainages towards southwest in the southern block. It is further observed that the ratio of valley floor width to valley height is very low (<8) in the river segment flowing along the WNW-ESE structure where the river might have been influenced by the on going activity of the structure. The slope induced by the reverse movement of the structure/fault results in the adjustments of drainage network in the form of channel blocks or shifts leaving paleochannels. The present study suggests that the structure, defined by the abandoned river channels, geomorphic anomalies, local seismicity and a brittle fault, is an active fault and capable of producing moderate seismic events.