MASW Imaging of the Deccan Basalt Lava Flows and Their Weathering Zones: A Case Study from Ghatia, India

The Deccan basalt province controls the hydrologic regime of an area of ∼500,000 km² in the central India. These basalts are largely layered flows with massive, vesicular and amygdaloidal varieties. We have studied the basalt sequence in the Ghatia micro-watershed in Madhya Pradesh, India, using the multichannel analysis of surface waves at several sites. The shear wave velocity sections reveal the layered nature of the basalt sequence with a cap of low velocity weathered zones. In some sections, the weathering zones are undulating. Interestingly, in some of the massive flows, there are low-velocity vertical zones that can be interpreted to be either vertical columnar joints or tectonic fracture zones. It is suggested that the low-velocity weathered flows can be the good groundwater reservoirs, and the vertical low velocity zones can efficiently transport ground water from one flow to the other flows. Geotechnical applications of the results are also discussed.