TIME DOMAIN MOMENT TENSOR INVERSION OF BALA-SIRAPINAR (CENTRAL TURKEY) EARTHQUAKES OF 2005-2008

The goal of this study is to analyse source parameters of Bala-Sirapinar (Ankara) earthquakes occurred during 2005-2008, and to explain the geometry of active fault structures and seismotectonic characteristics in the region by using seismological data. For this purpose, we have analysed 35 earthquakes with magnitudes ranging 3.5 ≤ M ≤ 5.7 occurred between 30.07.2005 and 18.12.2008. Methodology used in this study developed by Dreger (1992), Dreger and Helmberger (1993), and it is known as Time Domain Moment Tensor Inverse Code (TDMT_INVC). Regional Moment Tensor (RMT) method is commonly used to determine source parameters of moderate earthquakes (4.0 ≤ M ≤ 6.0) recorded at regional distances (1° ≤ Δ ≤ 10°), and it is widely accepted technique due to availability of number of high quality broad-band stations. With regard to the earthquake history of the region, there is not clear surface ruptures of active faults which can produce a major earthquake. Nevertheless, the study region has been affected significantly from earthquakes generated by North Anatolian Fault located 120 km to the north and cross-cutting fault zones (splay faults) to the south. We have consequently obtained focal mechanism and moment tensor solutions of 27 earthquakes which have good signal-to-noise (S/N) ratios. According to source mechanism solutions, right-lateral strike slip fault characteristics are common in NW-SE direction and left-lateral strike-slip fault characteristics in NE-SW direction. Some mechanisms include normal faulting components and partially E-W directions exist. It has known that the existence of conjugate fault systems are located both in NW-SE and NE-SW in region. In this respect, plenty of NW-SE directions indicate that common characteristics of 2005-2008 earthquake activity in this region could have represented with right lateral strike slip faulting mechanism and source mechanism solutions are consistent with active tectonics and local geological features.