Publication: Bala (Ankara) earthquakes: implications for shallow crustal deformation in Central Anatolian section of the Anatolian Platelet (Turkey)
Abstract
İç Anadolu depremsellik açısından sessizdir ve Anadolu bloğu içinde az da olsa 5.6 büyüklüğüne kadar depremler meydana gelmektedir. Türkiye’nin başkenti Ankara’nın güneydoğusunda 2005 ve 2007 yıllarında maksimum büyüklükleri 5.6 olan iki deprem dizisi meydana gelmiştir. Bu çalışmada, bu depremler ve artçı sarsıntılarından elde edilen sismolojik veriler ışığında Anadolu levhasının sığ kabuk deformasyonu tartışılmıştır. Ankara’nın Bala ilçesinde 20 Aralık 2007 tarihinde meydana gelen depremden sonraki ilk 24 saat içinde bölgeye yedi geçici deprem istasyonu kurulmuş ve yaklaşık 2 ay çalıştırılmıştır. Büyüklükleri 5.5>ML>0.8 arasında olan yaklaşık 920 arçı sarsıntının hassas lokasyonu yapılmıştır. Bu, Anadolu levhasının Orta Anadolu bölümündeki en iyi gözlemlenebilen deprem aktivitesidir. Ayrıca 2005 Bala depremleri de tekrar analiz edilmiştir. Çok iyi konumlandırılmış 20 Aralık 2007 depremi artçı sarsıntı dağılımı ve fay düzlemi çözümleri, Anadolu levhasının iç deformasyonu nedeniyle olası bir zayıflık zonunda (Afşar fay zonu) KB−GD yönelimli sağ-yanal doğrultu atımlı faylanmanın meydana geldiğini göstermektedir. Yapılan analizlerde, Bala depremlerinin Marmara Bölgesi’nde meydana gelen 1999 depremleri sonrasında daha doğudaki sismik aktivite artışıyla ilişkili olabileceğini göstermektedir.
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 (ML= 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>ML>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 Afşar 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.
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 (ML= 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>ML>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 Afşar 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.