Spectral decomposition of S-waves in investigating regional dependent attenuation and improving site amplification factors: A case study in western Greece

Seismic-hazard analysis is based on the knowledge of the factors that configure the wave attenuation properties due to the loss of energy radiated away from the source (geometrical spreading and anelastic attenuation) and the site amplification due to surface geological conditions (the so-called site effects). Both factors can be separately investigated based on Generalized Inversion Techniques (GIT), through spectral decomposition of earthquake recordings in terms of Fourier Amplitude Spectra (FAS). In this study a parametric GIT algorithm, was applied in western Greece, allowing a simultaneous spectral decomposition of S-wave records in order to estimate parameters controlling seismic motion. The analyses provided a regional variation of the quality factor, Q s between 23—91, with a geometric mean value of 45, a distance dependent geometrical spreading attenuation factor gamma, γ, smoothly decreased between 12 and 200 km, from 0.98 to 0.77, as well as Site Amplification Factors for both horizontal and vertical components of 24 sites located in the study area. Moment Magnitudes, M w and corner frequencies, f c , were computed for the examined earthquakes, indicating an increasing trend of stress drop, Δσ from ~ 6 to ~ 55 bar for M w = 2.5 to 5.2. The estimated values of these parameters, are in good agreement with the corresponding ones based on other methodologies, concluding to the relevant low average logarithmic misfit (~ 0.17) between observed and synthetic FAS. Consequently, attenuation and site amplification factors computed in this study, can provide rational input parameters for stochastic S-wave simulations, improving thus deterministic seismic hazard assessment.