Mapping Intrinsic and Scattering Attenuation in the Southern Aegean Crust Using S Wave Envelope Inversion and Sensitivity Kernels Derived From Perturbation Theory

We applied sensitivity kernels based on perturbation theory to map the crustal intrinsic and scattering attenuation of S wave envelopes in the southern Aegean. The southern Aegean crust is under extension due to the rollback of the Nubian plate, which is subducting beneath the Aegean plate. The waveforms of 104,531 crustal events (<40 km) were used to calculate S wave envelopes in four frequency bands. The S wave envelopes were modeled using the 3-D isotropic solution of the radiative transfer equation with a factor for energy leakage. A two-stage grid search with linear least squares was applied to estimate the attenuation parameters from each S wave envelope. Then we calculated the 2-D scattering and absorption sensitivity kernels for each wave path based on perturbation theory. These kernels and the envelope attenuation parameters were inverted using the Markov chain Monte Carlo algorithm to obtain maps of intrinsic and scattering attenuation (Q_i⁻¹ and Q_sc⁻¹). High Q_i⁻¹ has thermal origin associated with fluids while high Q_sc⁻¹ stems from velocity contrasts caused by deformed structure such as faults, folds, or fractures. The Corinth rift, the Santorini-Amorgos zone, and the Gulf of Gökova show strong extensional deformation, which may produce high Q_sc⁻¹. The deformed oceanic material accreted below the continental crust and fractures generated by large thrust earthquakes likely produce high Q_sc⁻¹ in Crete. The Corinth rift with its repeated earthquake swarms demonstrates fluid activity, which can explain high Q_i⁻¹. Thermal contrasts generated by metamorphic core complexes are a potential source of Q_i⁻¹ in Cyclades and Crete.