Search for buckling of the southwest Indian coast related to Himalayan collision

Microseismicity and moderate earthquakes occurring throughout Peninsular India indicate that stresses associated with the Himalayan collision may result in weak deformation of the subcontinent. One geometric response to stress in a thin elastic plate is the creation of buckles, a feature of the oceanic plate south of the Indian continent, but not normally a feature of continental deformation. Geomorphic studies of the Malabar coastline identify erosional and accretional coastlines, and occasionally invoke vertical neotectonics as an underlying cause for their observed distribution. In support of these geological observations are numerous historical accounts that suggest that coastal features have changed in the past 500 yr. We investigated several locations along the southwest coast of India where uplift or subsidence has been reported. We found that evidence for recent vertical motions is ambiguous along much of the coast but geologic, geomorphic, and tide-gauge data near Mangalore (13°N) confirm previous studies that require uplift relative to points to the north and south. Quaternary rates are lower than current rates indicated by tide-gauge data (≈3 mm/yr) and spirit-leveling data (≈6 mm/yr), but both are consistent with recent strain rates observed geodetically in southern India (<10 nanostrain/yr). Although the apparent wavelength of warping (200 km) along the west coast of India is symptomatic of buckling, the known rheological structure of India is not conducive to its development.