SOURCE INVERSION OF THE OCTOBER 1, 1995, DINAR EARTHQUAKE (M-S = 6.1)- A RUPTURE MODEL WITH IMPLICATIONS FOR SEISMOTECTONICS IN SW TURKEY

An earthquake of M-s = 6.1 devastated the town of Dinar (SW Turkey, po pulation 35,000) on October 1, 1995, killing 90 people and destroying 30% of the town. The earthquake generated complex body-waveforms varyi ng with azimuth at teleseismic distances. The method of complex body-w aveform inversion developed by Kikuchi and Kanamori (1991) was used to infer a source process for the earthquake. Two subevents were necessa ry to explain the observed seismic records. The inversion result sugge sts that the Dinar earthquake initiated at the SE end of the Dinar fau lt with a subevent of seismic moment M-o = 0.5 x 10(18) Nm. Six second s later, the second subevent took place about 10 km to the northwest o f the first subevent with a seismic moment a few times larger than the first. The CMT depths of the first and second subevents were found to be 10 and 15 km, respectively. Both subevents had a predominantly nor mal faulting mechanism with slip-vectors oriented NE-SW, showing good agreement with the velocity-vectors obtained from the recent SLR and G PS studies as well as with the regional stress orientation obtained fr om geological data. The main shock was preceded by foreshock activity concentrated at the SE end of the Dinar fault where the first subevent took place, while the aftershock activity was concentrated in the vic inity of the second subevent. The spatial distribution of the foreshoc k and the aftershock activities and the locations of the subevents sug gest that the first subevent broke an asperity and the second subevent broke a barrier on the fault, following the definition by Aki (1984) of an asperity and barrier earthquake model. About 10 km of surface ru ptures were associated with the earthquake while the estimates yield a rupture length of 25 km. The calculated source parameters of the sube vents and their locations suggest that the surface ruptures were proba bly associated with the first subevent. The estimates also show that t he rupture zones of the two subevents overlapped where the maximum ver tical displacement was observed. (C) 1998 Elsevier Science B.V. All ri ghts reserved.