Temporary strong motion observation and microtremor exploration around the Fujikawa-kako fault zone

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  • 富士川河口断層帯周辺での臨時強震観測と微動探査
  • フジガワ カコウ ダンソウタイ シュウヘン デ ノ リンジ キョウシン カンソク ト ビドウ タンサ

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<p>　We had conducted a temporary strong ground motion observation around the Fujikawa-kako fault zone in the eastern part of Shizuoka prefecture, Japan, for understanding of earthquake ground motion features in the area. In this paper we explain the outline of the strong motion observation and characteristics of observed ground motions. We calculated ratios of horizontal spectra of ground motion records at the stations to that of a rock reference site, and found that the large ratios are concentrated in the river mouth area of the Fujikawa river. The ratios at frequencies less than 0.8 Hz are particularly large in the coastal part of the mouth area. The spatial variation of the ratios at frequencies from 0.8 to 3 Hz is significant suggesting complex site amplification effects. On the other hand, the ratios are small at the stations in the southern part of Yamanashi prefecture. Small ratios are also found at the stations with firm soil conditions in the Izu peninsula and the western coastal part of the Suruga bay. We conducted microtremor array explorations at the stations to know shallow S-wave profiles. Average S-wave velocities in the top 30 meters were calculated from the profiles. We found that the spectral ratios in a frequency range from 0.8 to 3 Hz are well correlated with the average velocities.</p>

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