Site characterization of strong-motion stations of Himalaya and adjoining plains

Abstract

Site investigation is crucial for any strong-motion station’s installation due to the modifications caused by underlying soil strata on strong-motion records. Hence, this study focuses on the geophysical exploration of 54 strong-motion stations located in the Himalaya and adjoining plains to estimate the shear wave velocity (Vs) profile and depth of bedrock of underlying soil strata. The methodology adopted in this study for site characterization is the joint inversion of the surface wave dispersion curve and horizontal to the vertical spectral ratio of microtremor. Joint inversion of these two methods helps reduce the uncertainty in the results and provides deep VS profiles up to the bedrock. Such VS profiles would improve the results of ground response analysis required for seismic hazard assessment. The study results are presented in the form of complete VS profiles and essential parameters such as VS30 and depth of engineering bedrock. Seismic site classification is also presented using VS30 as a proxy. Site-class evaluated in the present study for several sites are compared with the results of earlier studies. The comparison of the site class shows dissimilarities for few site locations. The dissimilarity could be due to the adoption of indirect methods for site classification by earlier studies. The sensitivity analysis is also performed for evaluating the effect of possible uncertainties in VS profiles on ground response analysis. The results suggest that the VS profiles and site classes estimated in this study shall be preferred for future seismic hazard studies of the region.