Array measurements of long-period microtremors were conducted in Kawasaki and Yokohama cities in the Kanto basin to know S-wave velocity profiles for estimating strong ground motion. We observed long-period microtremors at 8 sites by installing temporarily two arrays at each site. Each array consists of 7 vertical seismometers with station spacing of 0.2 to 3km. Phase velocities of microtremors were estimated from an frequency-wavenumber analysis. They show dispersive features in a period range from 0.5 to 5 seconds, suggesting propagation of Rayleigh wave. The phase velocity data were inverted to S-wave velocity profiles of thick sediments by an inversion based on a genetic algorithm. The S-wave velocity profiles are mainly approximated by four layers with S-wave velocities of 0.4-0.6km/s, 1.0km/s, 1.7km/s and 3km/s, respectively. It was found that the S-wave velocity of the 3rd layer is site-dependent. The depths to the interfaces of these layers in the deduced profiles are in agreement with results of seismic refraction and reflection explorations.
No takes yet. Share an insight, caveat, or question.
Yamanaka et al. (1999) studied this question.