Joint Modeling of the Receiver Function and Horizontal to Vertical Spectral Ratio for Shallow Shear Velocity Structures

Joint Modeling of the Receiver Function and Horizontal to Vertical Spectral Ratio for Shallow Shear Velocity Structures

It has been proven, in our previous study, that receiver functions (RF) of strong-motion records are effective for estimating shallow subsurface structures, especially for bedrocks and basin structures. The shallow shear velocity profiles of over 700 strong-motion stations in Taiwan were estimated by modeling of receiver functions. The theoretical transfer functions of stations derived based on their velocity structures are calculated and compared with the average horizontal to vertical spectral ratio (HVSR) of historical records to evaluate the site amplification of the results. Most of the theoretical site amplifications agree well with the observed results. However, some stations show notable differences between the theoretical and observed amplification, indicating misestimates of the inverted velocity profiles from the receiver functions. Therefore, an approach is herein designed, termed the HVSREC method, to model the RF and HVSR jointly for estimating shallow velocity profiles beneath strong-motion stations, as RFs are primarily sensitive to velocity contrasts based on the time-domain converted phases, and HVSRs are also sensitive to velocity contrasts but based on the frequency domain site amplification. The joint modeling provides a reliable estimation of velocity structures that conform to the real site effects in the time and frequency domains. The velocity contrasts, generating the converted phases and controlling the site amplification, can be reconstructed in the estimated velocity structure. The differences between the results estimated from the RF, HVSR, and joint methods are also compared and discussed.