2019 Volume 72 Pages 8-16
We carried out microtremor observations with a miniature array in the coastal area of Kuji city, Iwate prefecture and we tried to estimate shallow S wave velocity structures using microtremor H/V and phase velocity dispersion curves. The site amplification factors from the engineering bedrock based on an average S-wave velocity were evaluated. Then, the SH wave amplification ratios as a function of frequency were also calculated by using the S-wave velocity structure model. The results are shown as follows: Shallow S-wave velocities in the coastal area of Kuji City were very slow and were about 100m/s. The estimated structure in this area indicated the bowl-shape. The amplification factors obtained from microtremor observations were larger than the site amplification factor of J-SHIS. The amplification characteristics of the SH wave showed that the maximum of the amplification factor was six times at a frequency of 1 Hz.