Higher modes of surface waves in microtremor analysis

We usually analyzed microtremors using a fundamental mode only. However, recent studies demonstrated that higher modes should be considered in SPAC method. In order to investigate this theoretically, we simulate microtremors numerically and applied the proposed method using higher modes. Also we applied this method to field data. In this method, we calculated apparent phase velocity from phase velocity and amplitude of higher modes, and compare the apparent velocity with the observed phase velocity. Since the phase velocity obtained from simulated data and field microtremor data is well consistent with the apparent phase velocity, the analysis method using the apparent velocity works well in S-wave velocity estimation.