A computational approach for bedrock regressions with diffuse field concept beneath the Japan Islands

The present computational approach using the theory of diffuse field concept for earthquake (DFCe) is introduced to retrieve the subsurface velocity structures at the whole K-NET and KiK-net stations and to estimate the associated uncertainties. Remarkable agreement could be achieved between the identified velocities retrieved from DFCe and those obtained from in-situ PS loggings. The effective bedrock depth (Deff) is assumed to correlate with the fundamental peak frequency (f0) based on a proposed quarter wavelength approach. The Deff must be larger than its corresponding wavelength (lambda) and have the minimum difference (Deff -lambda). The newly established frequency-depth regression needs to be defined as a function of the average S-wave velocity overlying the Deff. The f0 has correlation trends with the depths to the layers, where S-wave velocities >= 800 m/s and >= 3000 m/s. The outliers in these correlation trends exist because of unsatisfying the condition of the Deff.