Estimation of Phase Velocities of Love Wave From Three-Component Microtremor Array Observations By Using Spatial Auto-Correlation and Frequency Wavenumber Analysis

Abstract eng:
Microtremor array technique was a method to estimate S-wave velocity profiles by using dispersions of surface waves from microtremor array records. Rayleigh waves in vertical microtremors were frequently used because of convenient means of array measurements in fields. However, it was difficult to estimate parameters of Vs and thickness in the velocity profiles by using only the dispersions of Rayleigh waves. If other observable geophysical values, e.g. Love wave dispersions, can be used, the unique solvability will be better for the microtremor array technique. Our study tries to detect not only dispersion curves of Rayleigh waves but also those of Love waves from three-component microtremor array records by using threecomponent spatial auto-correlation (SPAC) technique and horizontal frequency-wavenumber (F-K) spectral analysis. At the ground of Iwate University in Morioka City in the northern Honshu Japan, the applicability of SPAC method and F-K method for estimating phase velocities of Love wave in microtremors using a three-component array consisting of 10 sensors was studied. As a result, SPAC method and FK method in different type triangular arrays with same sensor number with different orientations was able to obtain the same phase velocities. For the case of the circular array consisting of nine sensors on a circumstance with same radius and one at a center, both method gave better dispersion of Love wave in a wide frequency range. It was possible to obtain dispersion curves in a wide frequency band using arrays consisting of 10 sensors. In the horizontal microtremor analysis it was possible to obtain the phase velocities of the Love wave using both FK method and SPAC method in a wide frequency band.

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