The seismogenic fault of the 2010 Efpalion moderate-size seismic sequence (western Corinth gulf,Central Greece)

The 2010 Efpalion seismic sequence with two main moderate earthquake events occurred in the northwestern part of the Corinth Gulf (Central Greece)—a region that has been intensely stretched due to an on-going N–S extensional stress regime. Previous studies assign these two events to activations of (a) two faults dipping to the north with low angles; (b) two faults dipping at high angles, the first dipping to the south, and the second to the north; and (c) two faults dipping at high angles, but the first dips to the north, and the second to the south. The recently proposed TR method for focal mechanisms that identifies the seismogenic fault of an earthquake sequence is applied on the available focal mechanisms of the sequence, and its results are interrelated with the geology of the region, and previous contradictory interpretations. The focal mechanisms constructed with MT inversion define a steep north-dipping normal fault, whereas those constructed with first motions of P-waves define the activation of two adjoining faults that dip with high angles to the SSE and south, respectively, and which are characterized by strain (slip) compatibility. The latter option fits well with the geology of the region that is dominated by a SE to S-dipping horse-tail splay fault zone which exists at the eastern tip of the Nafpaktos Mountain Front. The application of the TR method reveals that the usage itself of different methods for the construction of the focal mechanisms complicates the problem of correctly identifying the seismogenic fault.