Three-Dimensional Crustal Seismic Velocity Structure of the Aitolo-Akarnania Region (Western Greece)

Western Greece poses significant challenges in terms of understanding its tectonic and deformation context. The Aitolo-Akarnania region of our interest is located in the eastern part of the Ionian Akarnanian Block (IAB). Its main active tectonic structures are the Katouna Stamna fault system (KSF, a left-lateral strike–slip fault that is north–south-oriented), the two east–west grabens of the Amvrakikos Gulf and Lake Trichonis, and the transition between the gulfs of Patras and Corinth. Using a new catalog with 18,710 seismic events, we determined the three-dimensional P-velocity and Vp/Vs structure of the crust by inverting P- and S-wave travel times. We explored a 3D grid with horizontal 10 km node spacing down to a depth of 40 km into 14 layers. The obtained 3D P-velocity and Vp/Vs fields clearly show the following: (1) lateral variations in seismic velocity down to a depth of 10 km, highlighting the heterogeneity of the upper crustal structure; (2) the crustal-scale KSF, which is associated with a high-Vp/Vs zone potentially influenced by fluids; (3) the graben structure of Trichonis Lake, which provides insights into its extensional tectonics through the characterization of its sedimentary fill to a depth of 10 km; and (4) a hypothetical immature decollement, dipping northwards until 25 km depth, at the transition between the gulfs of Patras and Corinth. Two seismic areas that have been observed for several decades—the eastern side of the Amvrakikos Gulf and the Pergandi Mountains—are also discussed.