Shallow Subsurface Velocity Structure using the ambient noise for the Himalaya Region.

Abstract

The Gorkha earthquake 25 April 2015 has attention the entire worlds to Himalaya due to large scale damage caused in the region. This heavy damage happened due to site amplification of the ground motion was clearly evident during the Nepal earthquake. The Himalaya situated in the central seismic gap (CSG) region suggested by Khattri (1987). Region itself has large possibilities of site amplification which can result high damage during future earthquakes. Average shear wave velocity up to 30 m depth are being described as Vs30. Correct estimates of Vs30 provides useful tool for site classification and site amplification at any location. This is important parameters for the engineering uses and is also used in seismic microzonation study of any area. In the present study Vs30 is measured in various locales of the Himalaya using the technique of multi-channel analysis of surface wave (MASW). Data has been acquired from the Sub-Himalaya to Lesser Himalaya for calculation of Vs30. Dispersion curves are obtained using the MASW data and are compared with the theoretical dispersion curve to obtain the shear wave velocity model at various point. Detail analysis of results obtained at various locations suggests that Vs30 in this region varies from 150 ms-1 to 900 ms-1.