Application of Geophysics in Landslide Studies - A Case Study from Manthada, Nilgiri District, Tamil Nadu

摘要

Electrical Resistivity surveys in the form of spot Vertical Electrical Soundings (VES) were conducted in Manthada landslide area of Nilgiri district, Tamil Nadu, to estimate the thickness of overburden / depth to bed rock. Twenty seven VES using Schlumberger array have been carried out over the study area. Interpretation of the field data suggests three and fourlayer earth sections to exist with thickness varying from 1 metre to more than 30 m. The bed rock has resistivity higher than 500 ohm.m. Resistivity lows and highs of the order of a few hundred ohm.m to a few thousands of ohm.m correspond to highly jointed to massive Charnockite rocks respectively. Depth to the bed rock or overburden thickness map reveals that the depth to bed rock is shallow in the western and north western portions whereas it is deep in the southeastern part varying from 2.5 metre to more than 30 metres in the surveyed area Apparent Resistivity, resistivity pseudo-section and depth to basement rock maps were prepared. The apparent resistivity maps bring out resistivity lows of order 200 ohm.m to 400 ohm.m disposed in NNE-SSW direction indicative of a weak zone which may be prone to landslides. On the other hand, high resistivity trends may indicate a stable land mass of massive charnockite rocks.