微動アレー探査における周波数-波数スペクトル法と空間自己相関法から推定したRayleigh波の有効波長範囲の上限の検討

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In a microtremor array technique phase velocities must be obtained in a wide-range of wavelength in order to estimate underground structures precisely. Frequency-wave number spectrum (F-K) method and Spatial auto-correlation (SPAC) method are used to estimate phase velocities of surface waves in microtremors. Recent studies using techniques of numerical simulation or field experiment show that SPAC method can observe longer wavelength possible to estimate phase velocities in microtremors than F-K method.We also examine and discuss the upper limits of wavelength calculated using microtremor array data by the two kinds of methods. For the above purpose, microtremor array observations were carried out in four sites of Morioka city, Iwate Prefecture. The array configuration is a triangle with seven vertical seismometers. The array size defined by the distance between a center and an apex of the triangle ranges from 10m to 100m. Three or four arrays with different sizes were used at one observation site. Phase velocities of Rayleigh wave in microtremors were observed by F-K method and SPAC method. We defined a standard phase velocity which was calculated from all the array records at one site. To estimate the upper limits of wavelength, a residual between standard phase velocity and observed phase veloclty for each array was defined with in 0.1. The range of the estimated upper limits of wave lengths by F-K method were from 2.3 to 6.8 times for a distance between a center and an apex of the triangle array, and those by SPAC method were ranging from 3.2 to 17.2 times. These results show that SPAC method can observe longer wavelength possible to estimate phase velocities in microtremors than F-K method.
2002-10-01

微動アレー探査における周波数-波数スペクトル法と空間自己相関法から推定したRayleigh波の有効波長範囲の上限の検討

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