Estimation of shearwave velocity in drifts using multichannel analysis of surface wave (MASW) technique — A case study from Jammu & Kashmir, India

Multichannel analysis of surface waves (MASW) is a non-destructive seismic prospecting method utilizing Rayleigh waves for imaging and characterizing shallow sub-surface structure. Multichannel analysis of surface waves (MASW) studies were conducted in drift areas of two bridge sites in the hilly terrain of J&K for imaging and characterizing shallow sub-surface structure. The purpose of the present study is to estimate the shear wave velocity (VS) and subsurface structure in four drifts made in a hilly terrain for construction of two bridges. Rayleigh waves are having dispersive properties, travelling along or near the ground surface and are usually characterized by relatively low velocity, low frequency, and high amplitude. The study area comprises of Tertiary group of rocks which are underlain by Siwalik group. The main rock type in the study area is dolomite which has undergone various geological processes like weathering, jointing, fracturing and shearing. MASW data was collected inside four drifts in the mountainous terrain of J&K state which are located on either sides of Chenab river. The data was analyzed by relevant processing software using dispersion and inversion technique. Shear wave velocities were estimated up to 30 m depth. Average shear wave velocity (VS30) up to top 30m was also computed. It is observed that, VS in the range 400–800 m/s upto 10–15 m corresponding to weathered rock, followed by compact dolomite rock up to the depth of about 30 m with VS in the range 1200–1600 m/s. Some low velocity zones are also identified from these sections which represent shear zones.