APPLICABILITY OF A SPATIAL AUTOCORRELATION METHOD (SPAC)USING A LINEAR ARRAY IN COMPARISON WITH TRIANGULAR ANDL-SHAPED.ARRAYS

摘要

We have examined the applicability of a spatial auto-correlation (SPAC) method using a linear array in comparison with triangular and L-shaped arrays. The SPAC requires two dimensional arrays, such as a circle, a triangle and a crossing for calculating the phase-velocity of the microtremor. Theoretically, isotropic arrays; such as a circle or an equilateral triangle, are preferable in the SPAC analysis. However, the isotropic arrays required wide space and it is difficult to obtain such wide space in urban area. Recently, several theoretical and experimental studies have shown the validity of irregular arrays. Results of these studies have also implied the validity of linear arrays in which receivers are placed only on a line. The use of linear arrays will enable us to apply passive methods in urban area much easily. In this paper, we are going to examine the applicability of the linear array in terms of numerical simulation and field experiments. The result of field experiment showed that the linear array provides almost identical dispersion curves as that of two dimensional arrays although numerical simulation showed clear disadvantage of the linear array. It implies: that that the sources of the microtremor are distributed, randomly in space and the microtremor does not have any specific propagation direction at most of sites