Spatial Distribution of Random Velocity Inhomogeneities in the Southern Aegean From Inversion of S Wave Peak Delay Times

The southern Aegean is characterized by an ongoing process of oceanic subduction. In this study, 1,718 intermediate depth (>35 km) events recorded in the southern Aegean are used to calculate the peak delay times (t_p). The t_p are measured as the time difference between S wave onset and the peak of the S wave envelope in 2-to 4-, 4- to 8-, 8- to 16-, and 16- to 32-Hz bands. The t_p are also inverted to estimate the scattering parameters (κ and ε_param) and power spectral density function (P (m)) at large wave numbers (m = 15 km⁻¹ or m_l) of the medium modeled as von Kármán type. κ controls frequency dependence of scattering while P (m_l) represents the scattering strength in high frequencies for ɑm_l >> 1 (ɑ = correlation length of inhomogeneities). High P (m_l) with low κ across Peloponnese in 0- to 20-km depth may result from intermixing of oceanic material with continental rocks at different levels with a possibility of fluid activity and salt diapirism in northwest Peloponnese. Moderate P (m_l) in 0- to 60-km depth across Crete is likely due to a combination of factors including past megathrust earthquakes, sediment underplating, and flow of metamorphosed material in a subduction channel. Cyclades shows low κ in 0- to 40-km depth, indicative of inhomogeneities produced by metamorphic core complexes. Very low κ in 60- to 80-km depth is consistent with the location of mantle magma reservoir in the back-arc region. Our results suggest that a significant portion of total S wave attenuation (Q_s ⁻¹) in eastern Cyclades for 20- to 80-km depth may be due to scattering losses.