Velocity structure inversion from H/V spectral ratios of earthquake data: Application to the Tohoku region, Japan

Abstract : In this study we focus on sites where the site effect for seismic ground motions can be described using a one dimensional model. Previous studies show that the imaginary part of the Green's function at the free surface is proportional to the square of the absolute value of the corresponding transfer function for a plane, vertically incident wave with unit amplitude. It is then possible to carry out an inversion of the 1D velocity structure using the relationship between the horizontal-to-vertical (H/V) spectral ratio and the ratio of horizontal and vertical transfer functions. We carry out inversions of the velocity structure for three sites of the KiK-net network in the Tohoku area, Japan, following the proposed theory for earthquake H/V ratios. We verify that there is a good match between the earthquake H/V ratio and the transfer function corresponding to the new proposed velocity structure for the three sites studied in the present work.