Estimation of 3D S-wave velocity model of deep sedimentary layers in Kanto plain, Japan, using microtremor array measurements

摘要

Array measurements of long-period microtremors were conducted at 22 sites in the Kanto basin to explore S-wave velocity profiles for estimating long-period ground motion. Two arrays were temporarily deployed at each site. Each array consists of 7 vertical seismometers with a station spacing of 0.2 to 3 km. A frequency wavenumber spectral analysis was applied to the array records to obtain frequency-dependent propagation direction and phase velocity. The phase velocities at all the sites are dispersive from 0.3 to 5 seconds suggesting propagation of Rayleigh waves. The phase velocity at each site was inverted to a 1D S-wave velocity profile of the sedimentary layers over the basement with an S-wave velocity of about 3km/s using a genetic inversion technique. A 3D S-wave velocity model for the Kanto basin was constructed compiling the estimated S-wave profiles and S-wave data from previous researches.