Differences between site characteristics obtained from microtremors, S-waves, P-waves, and codas

We examine differences of empirical site characteristics among S waves, P w aves, coda, and microtremors using records at 20 sites in and around the Se ndai basin, Japan, and interpret the differences theoretically. At soft soi l sites the horizontal-to-vertical spectral ratios (HVRs) for early P coda become different from HVRs for a P wave with increasing time and eventually converge on HVRs for microtremors. The HVRs for an S coda become similar t o HVRs for microtremors with increasing time in the frequency range lower t han 3 Hz at soft soil sites. By contrast, at a rock site and two hard soil sites, HVRs for S coda agree well with HVRs for an S wave. The soil-to-rock spectral ratios for horizontal (HHRs) and vertical (VVRs) components for e arly S coda are larger than those for an S wave at soft soil sites. When we use the deep sedimentary structures above the bedrock before Tertiary age, theoretical HVR for the fundamental mode of Rayleigh waves is consistent w ith observed HVR for microtremors and theoretical HVR for an obliquely inci dent SV wave is consistent with observed HVR for an S wave. Theoretical S-w ave site amplification factor explains well observed HHR for S wave but doe s not coincide with HVR for microtremors. In general the frequencies of max imum peaks of HVRs for microtremors do not coincide with those of HVRs and HHRs for S wave. However, if we select HVRs with peak frequencies lower tha n 1 Hz and peak amplitudes larger than three, the peak frequencies of HVRs for microtremors roughly coincide with those of HVRs and HHRs for S wave. E ven under these constraints, their amplitudes do not coincide with each oth er. Concerning: coda, we conclude that the Rayleigh wave contamination in c oda is significant in the frequency range lower than 3 Hz at soft soil site s.