INVERSION OF SOURCE PARAMETERS FOR SUBCRUSTAL EARTHQUAKES IN THE HELLENIC ARC

A one‐station method was developed to invert simultaneously for seismic moment, focal depth, and the orientations of the nodal planes. This method was tested on seismograms recorded at the broadband Gréfenberg array (GRF) for earthquakes in the central to eastern Hellenic arc and southern Turkey. The complete P and S body‐wave responses, including all near source surface reflections, were synthesized using the reflectivity method. The minimum misfit between the observed and theoretical seismograms in the WWSSN‐LP band was determined by cross‐correlation, searching the whole parameter space of strike, dip and rake of a pair of orthogonal nodal planes, and adjusting the source depth and seismic moment. The initial searching step of 20° was reduced to 5° in the vicinity of the minimum misfit position, for a final search. The best fitting solution was then compared to the Harvard (HRVD) moment tensor solution best double couple which was derived using long‐period data and to the P‐wave first motion polarities reported by the ISC. Most solutions based on GRF data agree well with those found by HRVD, but in some cases some features of the observed GRF signals cannot be matched by the HRVD solution or solutions similar to it. The nine earthquakes we analysed in detail had magnitudes between 5.2 and 5.8. Our depth determinations ranged from 35 to 155 km. The deepest events (80–155 km) were located near Rhodes and to the east of it. One earthquake located in southern Turkey was confirmed to have a focus at about 125 km depth. The focal mechanisms of the intermediate depth earthquakes in the eastern Hellenic arc show P‐axes approximately parallel to the strike of the deep slab. Copyright © 1990, Wiley Blackwell. All rights reserved