Rupture process and spectra of some major Turkish earthquakes and their seismotectonic implications

Abstract

The teleseismic body waveform inversion of 18 large earthquakes in Turkey wereexamined in order to understand rupture processes of these earthquakes. The totalseismic moments thus obtained were compared with the moments estimated from theirspectra. The earthquakes were choosen from different tectonic regimes; 3 from theNortheast Anatolian block that undergoes a continental collision between Arabia (LIlelEurasia, 1 from the East Anatolian Fault Zone (EAFZ) that accomodates the motionbetween the Turkish and Arabian plates, 1 from the Northeast Anatolian Fault (NEAF)which is the northern border of the Northeast Anatolian block, 1 from the Bitlis ZagrosThrust and Fold Belt which is the southern border of the Northeast Allatolian block,3 from the North Anatolian Fault Zone that accomodates the motion betweell Turkeyand Eurasia, 4 from the Western Turkey which is subject to N-S extellsioll, 3 from theAegean Sea, 1 from the Black Sea region, and 1 from the Cyprus region tha,t representsthe motion between Africa and Turkey.The teleseismic records were obtained from WWSSN, GDSN and IRIS data centersand the method of complex body wave inversion developed by Kikuchi alld Kanamori(1991) was used. The results indicate that most of the earthquakes haviug magnitudesof Als :2: 6.8 show complex rupture patterns as revealed by the space aml time distributionsof the subevents which provide information on the details of rupture process.The total seismic moment tensor comprised from the moment tensors of the individualsubevents represents well both the overall tectonic stress regime in the source regionand the observed surface ruptures. The estimated moment magnitude for each eventwas found to be directly related to the surface magnitude in the magnitude range of.5.5 - 7.:3 range.The conclusions of this study are as follows: (1) The northward motion of theArabian plate with slip rate of 24.4 mm/yr is accomodated along the EAF and theBitlis Zagros Thrust and Fold Belt with slip rate of 5-6 mm/yr, as inferred from the1971 Bing()l and 1975 Lice earthquakes. (2) Although the focal mechanisms of the maillsubevents of the 1975 Lice and 198:l Horasan-Narman earthquakes have nearly equallen-lateral strike-slip aud thrust faulting components as also reported by the otherinvestigators. The total seismic moment tensor of this event shows a predominantthrust faulting with E-W strike which is more compatible with the observ(~d rupturesas well as the stress regime in the region. (:3) Not all, but most of til(-' multiple eveutshave a non-double-couple component, resulting from subevents with different faultorientations. (4) The seismic moments determined in frequency domain are drasticallydependent on the radiation pattern correction. This fact could be used as a llsf'ful toolill v('ryii Ilg the source IlWcil<tllislll soilltioll uj' earthquakes.