Array Measurements of Long-period Microtremors in Southwestern Kanto Plain, Japan

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  • YAMANAKA Hiroaki
    Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology
  • SATO Hiroaki
    Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology Present Address: Central Research Institute of Electric Power Industry
  • KURITA Katsuml
    Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology
  • SEO Kazuoh
    Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology

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Other Title
  • 関東平野南西部におけるやや長周期微動のアレイ観測
  • 関東平野南西部におけるやや長周期微動のアレイ観測--川崎市および横浜市のS波速度構造の推定
  • カントウ ヘイヤ ナンセイブ ニ オケル ヤヤ チョウシュウキ ビドウ ノ アレイ カンソク カワサキシ オヨビ ヨコハマシ ノ Sハ ソクド コウゾウ ノ スイテイ
  • 川崎市および横浜市のS波速度構造の推定
  • Estimation of S-wave Profiles in Kawasaki and Yokohama Cities

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Abstract

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.

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