SOURCE MECHANISMS OF RECENT EARTHQUAKES IN THE HELLENIC ARC FROM BROAD-BAND DATA

Three-component long-period seismograms from the Global Digital Seismic Network (GDSN) are used to determine the focal mechanisms of recent large (m(b) > 5.5) earthquakes in the Hellenic arc, using the relative amplitude method. Results are consistent with the regional stress regime obtained from other methods but they are better constrained. Broadband seismograms have been deconvolved from GDSN short-period data and preliminary modelling of the P-phases has been carried out using a two-dimensional finite dislocation model. This results in better fits to the data than earlier models using point-source trapezoids as a source-time function. The relatively shallow hypocentral depths and stress drops typical of interplate contact zones (30 bar) are consistent with previous observations. This latter contrasts with the relatively low intraplate earthquake stress drops (< 15 bar) reported for back-arc events using the same technique.