Abstract
During the 1948 Fukui earthquake, heavy damage was experienced in and around the Fukui City. Most of the heavily damaged areas concentrated in the Fukui plain covered with sediments. This suggests that the sedimentary layers can be one of the most important factors to elucidate the damage distribution. In this study, S-wave structures were explored in the Fukui plain from microtremor array measurements. Vertical microtremors were observed in two arrays with station spacing from 0.1 to 2km at 5 sites in and around the Fukui plain. The Rayleigh wave phase velocities in a period range from 0.4 to 2 seconds were estimated from a frequency-wavenumber spectral analysis. The phase velocities at each site were inverted to a 1D S-wave profile using a genetic inversion. The profiles are characterized by 4 layers with S-wave velocities of 0.4, 0.67, 1.8 and 3.2km/s, respectively. The top layer is absent in the profiles at the sites in the margin and out of the plain. The depth to the third layer is about 0.2km at all the sites. However, the basement depth is 1km in the center of the basin and shallow at the marginal part.
