The 2014 Cephalonia Earthquakes: Finite Fault Modeling, Fault Segmentation, Shear and Thrusting at the NW Aegean Arc (Greece)

Abstract

We present refined finite fault models (FFM) for the 2014 Cephalonia (Keffalinia, Kefalonia) seismic sequence (Mw ~ 6.0), at the NW edge of the Aegean Arc (Ionian Sea). The area represents the seismically most active part of Europe and a continental promontory in which fault modeling is a challenge because of structural complexity and poor coverage by seismological, GPS and InSAR data. Inversion was based on GPS data and a new algorithm permitting fusion of slip vectors of individual earthquakes and of their cumulative dislocation and accepting constraints and collocation-type analysis of uncertainties. Computed FFM, which correspond to an essentially strike-slip fault and a blind, shallow oblique slip thrust, were assessed by sensitivity analysis and InSAR data and are consistent with the tectonic fabric of the area. They can also explain the observed extreme peak ground accelerations. The 2014 faults, in combination with FFMs of the 2003 and 2015 Leucas (Lefkada, Lefkas) earthquakes farther NE and of the 1983 M7.0 earthquake farther SW, constrain a > 100 km long immature, strike-slip fault zone along/close to the Cephalonia–Leucas coasts. This fault pattern, previously regarded as a poorly documented Cephalonia Transform Fault, consists of occasionally overlapping oblique slip segments with variable geometric and kinematic characteristics in a shear zone landwards of the plate interface, as evidence from seismic profiles reveals. This pattern may explain the enigmatic superimposition of shear and compression in the NW edge of the Aegean Arc.