A Frequency-Dependent Model for the Shape of the Fourier Amplitude Spectrum of Acceleration at High Frequencies

Publisher Website
Google Scholar
Abstract
The high-frequency decay term of the acceleration spectrum kappa is a commonly used parameter in engineering seismology. In recent years, the assumption of a linearly decaying spectrum in log-linear space has been recognized to not always be valid as the value of kappa depends on the analyzed frequency band. We present an alternative model for the spectral falloff in which the frequency dependence is explicitly taken into account. This is motivated by observations that the quality factor Q has a power-law dependence on frequency at high frequencies. The new model describes the spectral decay with the help of two variables, opposite to the single parameter kappa. The approach is applied to borehole data of the EUROSEISTEST site in Greece. The misfit between modeled and observed spectra is reduced with the new approach compared with the classical kappa model. The new estimates compare well with kappa estimates if the same frequency interval is considered but additionally allows for the capture of the frequency dependence of the spectral shape.