Fault Model for the 2015 Leucas (Aegean Arc) Earthquake: Analysis Based on Seismological and Geodetic Observations

The 17 November 2015 M-w 6.6 earthquake in Leucas (Leukas, Lefkas, or Lefkada) Island in the Ionian Sea, western Aegean arc, was modeled using teleseismic long-period P and SH waveforms and Global Positioning System (GPS) slip vectors. Detailed fault modeling in this region, characterized by intense seismicity and deformation rates, usually assigned to the Cephalonia Transform fault, is a challenge because of the unfavorable observation system. To overcome this problem, we independently analyzed seismological and geodetic data and then jointly evaluated the results. The adopted model indicates that the 2015 earthquake can be assigned to a shallow strike-slip fault, with a minor component of thrusting, along the southwest coasts of Leucas and with relatively high slip for the area. Additionally, mostly lowangle fault solutions satisfying geodetic observations were identified but were not further investigated. The preferred fault model permits recognition that recent M-w > 6.0 earthquakes in the area, some marked by extreme peak ground accelerations, are associated with a string of strike slip (or oblique slip), occasionally overlapping fault segments with variable characteristics, along or close to the west coasts of Leucas and Cephalonia (Keffalinia, Kefalonia) Islands, whereas the catastrophic 1953 M-w 7.2 Cephalonia and other previous major earthquakes were associated with thrust faulting.