Anatomy of the Right‐Lateral Strike‐Slip Cephalonia Fault to the Western Hellenic Arc Frontal Thrust

The region offshore the Ionian Islands (Kefalonia or Cephalonia, Lefkada, Zakynthos, and Ithaca), western Greece, is characterized by very high seismogenic and tsunamigenic potential. Despite numerous studies, many questions remain regarding the structures and kinematics in this area. Here, the right-lateral Cephalonia Transform Fault divides the Hellenic Arc from the Albanian compressional system. Historically, this area has been hit by several destructive earthquakes, such as the 1953 sequence (Mw >6) that destroyed Cephalonia. To improve the understanding of shallow sediment deformation, fault geometry and potential hazard, we carried out two oceanographic cruises (May 2022 and June 2023) during which a significant multiscale and multidisciplinary geophysical and geological data set has been collected. These data allowed us to define the deformation style of sediments at the intersection between the Cephalonia Fault and the thrust fronts of the Hellenic System, and the geometry of the Cephalonia Fault. The Fault, south of Cephalonia, opens in a 25 km-wide fan composed of elongated, sigmoidal, positive flower structures - features indicative of transpressive tectonics regime. In the area to east of Cephalonia we mapped for the first time a series of seaward-verging anticlines with strike-slip component and uplifted blocks. While to southeast of Cephalonia the deformation regime changes, becoming dominated by extensional and large landslides, affecting mainly superficial sediments. These new data allow us to map the transition between the transcurrent and compressional domains, unveiling the geometry of the faults laying the foundation for future studies on slip rates and seismic hazard.