Earthquake source parameters as inferred from the body waveform modeling, southern Turkey

Focal mechanism parameters of some significant earthquakes from southern Tu rkey have been estimated using either the body waveforms or the first motio ns of P-waves. It is observed that fault plane solutions derived from first motions may not be well constrained and may often be in error because of p oor signal-to-noise ratios at some stations, poorly distributed recording s tations in azimuth, lack of recognition of the reversed polarities at some stations, and positions of stations in terms of the crustal velocity struct ure, focal depth and, hence, take-off angles in the source area. The use of the inversion method introduces a considerable improvement in the focal pa rameters estimated in previous studies that have been used to construct sei smotectonic models in the study area. The focal depths inferred from the in version of body waveforms for the earthquakes occurring in southwestern Tur key are compatible with those reported by the ISC bulletins and other previ ous studies while the focal depths of earthquakes from the Antalya Bay are found to be less than those given by different agencies. Waveform inversion of earthquakes that have occurred in and around the Antalya Bay implies a low velocity layer showing azimuthal dependence. Hence, depth of rupture an d lateral extent of velocity structure are of importance in the investigati on of earthquake faulting process in this area. The source time duration of shallow earthquakes is generally longer than that for the deep focus earth quakes from the Antalya Bay and the Rhodes area. The events with relatively short and simple time functions may be interpreted as low stress drop even ts relative to the crustal ones. (C) 1999 Elsevier Science Ltd. All rights reserved.