2019 Volume 72 Pages 25-33
In order to utilize not only the Rayleigh wave but also the Love wave for microtremor array survey, we verify the effectiveness of frequency wavenumber analysis (FK) method extended to horizontal components of microtremors by Saito (2007). An FK analysis seems to be practically effective because the arrangement of observation positions can be an arbitrary shape. In addition, this FK analysis has an advantage that it is not necessary to rotate radial / transverse coordinate system from EW / NS coordinate system. In this study, we used the FK analysis by Saito (2007) and a spatial autocorrelation (SPAC) analysis for microtremor records observed with a triplet triangle array consisting of 10 sensors whose radius is changed every 3 times in order to try to estimate phase velocities of Love wave. We could obtain phase velocities of transverse and radial components by the two methods. The phase velocities obtained from the FK method were approximately equal to the phase velocities obtained from the SPAC method. In the case of the radial FK analysis, phase velocities of higher mode Rayleigh wave which were faster than ones of the fundamental mode one were detected in the high frequency band. The Love wave power fractions calculated by SPAC analysis showed to be 40 % - 60 % in the ground of Faculty of Science and Engineering, Iwate University. Since Love wave and Rayleigh wave were present at almost the same ratio at frequencies of 3 Hz to 13 Hz, it was thought that an estimation of both Love wave and Rayleigh wave succeed.