STUDY ON EVALUATION METHOD FOR VERTICAL SEISMIC GROUND MOTION IN S-WAVES CONSIDERING THE SIMULTANEOUS INCIDENCE OF SV-WAVE AND P-WAVE

In this study, we examined an evaluation method of the vertical component of S-waves part in sedimentary layers. In the study of Kyuke et al.(2010), we have proposed an evaluation method of vertical motion by simultaneous incidence of P-wave and SV-wave, using vertical array records. However, there was a problem that the simulation results couldn't explain the observed records in certain frequency range. First, in order to improve the simulation accuracy, we focused on the estimation method of the incident wave. In the study of Kyuke et al.(2010), the incident wave inferred only from the deepest sensor's records of vertical array. In this study, we introduced a new technique that estimates the incident wave using all of the vertical array records. Then, we simulated the records at an observation point where vertical array observation down to the seismic basement has been conducted at 6 depths. As to the transfer function and response spectrum, simulation results of vertical component were shown to be better consistent with the observed value than the results of SV-wave oblique incidence or P-wave vertical incidence. Next, we examined the ratio of P incident wave to S incident wave. It has been shown that the average ratio of the six records was distributed between 0.4 and 2.0 in the frequency range of 0.1Hz to 20Hz. Furthermore, in order to confirm the validity of this method, we examined the inferred incident wave. Using the incident waves at the above station, we simulated the records of nearby site. The calculated waves have well explained the observed records of both of the vertical component and the radial component.