首都圏における微動アレイ観測による堆積層のS波速度構造の推定(<特集>首都直下地震防災・減災特別プロジェクトPart 2)

概要

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Microtremor array explorations were conducted at 33 sites in the Tokyo Metropolitan area to estimate the S-wave velocity profiles of deep sedimentary layers. The purpose was to provide data required to understand the characteristics of long-period strong ground motions in the area. Two arrays spaced at intervals from 0.3 to 1.5km were temporarily installed with seven vertical seismometers at each site to record vertical microtremors over periods of 30 to 90 minutes. We applied a frequency-wave number spectral analysis to the array records to obtain Rayleigh wave phase velocity at periods from 0.5 to 6 seconds. The phase velocity at each site was inverted to an S-wave velocity profile down to the basement with an S-wave velocity of 3km/s using hybrid heuristic inversions. The resultant S-wave velocity profiles were compared to previous 3D models of the area. We found differences between our results and the previous results mainly at sites located in mar ginal parts of the basin. This comparison clearly indicates the need for future improvements to the existing 3D S-wave velocity model in the area.
2010-02-26