Focal mechanism and source time function of selected aftershocks of the Egion 1995 earthquake, Gulf of Corinth, Greece

Numerous aftershocks, which followed the 1995 Egion earthquake of magnitude Ms = 6.2, were recorded by the seismic network PATNET of the University of Patras and by a temporary local network EGINET. The well recorded aftershocks were located by the Patras Seismological Centre, University of Patras. The complete data set, received from the Centre, contains the records of over a hundred events. The spatial distribution of their epicentres forms an E-W elongated cloud with a central cluster and a few stray-away epicentres west and north-west from the cloud. The events from the central cluster, which is the source area of the main shock, that occurred during the first decade of August 1995, were selected for the analysis. Additionally, a few events from the small cluster located west of the main one were also analysed. Altogether, it was possible to perform the moment tensor inversion in the time domain for 29 aftershocks from the main cluster and for 4 events from the small cluster. The selected aftershocks have moment magnitude ranging from 1.7 to 3.2. The source time function of the larger events was determined by the empirical Green's function technique. The records of several pairs of large-small aftershocks, close to each other and with similar focal mechanism, were selected for deconvolution. The source time function was recovered for 5 larger aftershocks from the central cluster and for 3 events from the small cluster. The small number of available stations used for the moment tensor inversion limit stable results to the constrained double couple solutions. The solutions show a mixture of various types of the focal mechanism, though dip-slip events prevail over strike-slip events, and normal faulting prevails over reverse faulting. The pulse widths of relative source time functions depend on the station azimuth, indicating that the ruptures propagated unilaterally. The azimuth of rupture direction ranges from about 90 to 250 degrees with the dominant direction of about 200 degrees. The fracture velocity ranges from 0.4 to 0.8 of the shear wave velocity. The obtained results indicate complexity of the stress distribution in the source area of the Egion earthquake.