The 2005-2007 Bala (Ankara, central Turkey) earthquakes: a case study for strike-slip fault terminations

Abstract

An intense seismic activity has been observed after the Bala (Ankara, NW central Turkey) earthquakes (30 July 2005: Mw=5.3, 20 December 2007: Mw=5.4, and 26 December 2007: Mw=5.3), continuing up to the present. The epicenters and the focal mechanism solutions of the earthquakes indicate that the right lateral strike-slip Afar fault, trending N55-60 degrees W, is responsible for the main shocks. The Afar fault is thought to be the NW continuation of the Tuzgolu fault zone, which is one of the main neotectonic elements in central Anatolia. On the other hand, the aftershock distributions of the 2005 event have a NNE trend, and those of the 2007 event show a NW trending. Some focal mechanism solutions of the 2005 Bala earthquake aftershocks indicate normal and oblique normal faulting that corresponds to the NNE-trending Karakecili fault. It seems that seismic activation of the NNE-trending Karakecili fault was triggered by the 2005 main shock (Mw=5.3) that occurred on the NW-trending right lateral strike-slip Afar fault. The overall neotectonic framework is that the northwestern edge of the Tuzgolu fault zone, represented by the Afar fault in B ala, terminates in an extensional system represented by the oblique-slip Karakecili fault.