Bala (Ankara) Earthquakes: Implications for Shallow Crustal Deformation in Central Anatolian Section of the Anatolian Platelet (Turkey)

Abstract

Central Anatolia is quiet in terms of seismic activity, and rarely earthquakes up to magnitude 5.6 occur in the inner part of the Anatolian block or Anatolian platelet. Southeast of Ankara, the capital city of Turkey, two earthquake sequences with maximum magnitude of 5.6 occurred in 2005 and 2007. We discuss these shallow crustal deformation in the Anatolian platelet, in the light of seismological data from these earthquakes (M(L) = 5.6) and their aftershocks. Following the earthquake of December 20, 2007 near Bala town, Ankara, we installed seven temporary stations in the first 24 hours to observe the aftershock activity and these operated for more than 2 months. Approximately 920 aftershocks with magnitudes 5.5>M(L)>0.8 were located precisely. This is the first well-observed earthquake activity in the Central Anatolian section of the Anatolian platelet. We also re-analyzed the 2005 Bala earthquake sequence. The distribution of the well-located aftershocks and the focal mechanism solutions of the December 20, 2007 event define NW-SE-oriented right-lateral strike-slip faulting on a possible weak zone, namely the Afsar fault zone, as a result of the internal deformation in the Anatolian platelet. Our analyses seem to indicate that the Bala earthquake sequences are probably related to increasing seismic activity, following devastating 1999 earthquakes in the Marmara region, to the west.