Upper crustal structure of the western Corinth Gulf, Greece, inferred from arrival times of the January 2010 earthquake sequence

The western part of the Corinth Gulf attracts attention clue to its seismically active fault system and considerable seismic hazard. A moderate size earthquake occurred close to the town of Efpalio on January 18, 2010, followed by a sequence of smaller earthquakes. In the present paper we use this sequence to derive a local structural model for the region in the vicinity of Efpalio. The model is based on the minimization of travel-time residuals. In particular, we used arrival times from 51 selected events recorded 017 January 19 and 20 by at least 5 stations at epicentral distances less than about 25 kin. A variant of the method of conjugate gradients has been used for this purpose. In comparison with several previous models, the new model is characterized by higher velocities to a depth of about 8 km. The velocity ratio in the model is upsilon(P)/upsilon(S) = 1.83. The hypocentres of the selected earthquakes lay at depths between about 5 and 9 km, but their distribution is rather irregular.