Extensional Neotectonic Regime through the NE Edge of the Outer Isparta Angle, SW Turkey: New Field and Seismic Data

The Akflehir-Afyon Graben (AAG) is a 4—20-km-wide, 130-km-long NW—trending depression that separates central Anatolia in the NE and the Isparta Angle (IA) in the SW. Its southwestern margin-bounding fault determines the northeast edge of the outer IA that was previously interpreted as a compressional neotectonic structure, whereas our field evidence and recent seismic data substantiated that it is an oblique-slip normal fault characterising an extensional neotectonic regime. The AAG has an episodic and asymmetrical evolutionary history. This is indicated by two superimposed graben infills and structures. The older infill is folded, thrust-faulted and Early-early Middle Miocene in age. The younger infill is undeformed (nearly horizontal), Plio-Quaternary in age, and overlies the older infill with angular unconformity. Total throw amounts accumulated on both SW and NE margin-bounding faults, namely the Akflehir Master Fault (AMF) and the Karagoztepe Master Fault (KMF) since the Late Pliocene and Early Pleistocene, are 870 m and 200 m, respectively. Assuming a uniform motion, these values indicate motion rates of 0.3 mm/yr and 0.2 mm/yr, respectively, and the asymmetrical nature of the AAG. Kinematic analysis of surface slip data of both the AMF and KMF showed an oblique-slip motion with a minor right-lateral strike-slip component, and a NE—SW- directed extension. They also fit well with results of focal mechanism solutions of two recent seismic events, namely the 2000 December 15 Sultanda¤› (Mw=6.0) and the 2002 February 3 Cay (Mw=6.5) earthquakes. They have been sourced from the reactivation of the Akflehir-P›narkaya and Sultanda¤›-Maltepe sections of the AMF. The Cay earthquake caused devastating damage to structures and loss of life in the region. The Cay earthquake has also led to the development of ground ruptures and surface deformation. The geometry of the ground ruptures and focal mechanism solutions of both earthquakes proved once more that the southern margin-bounding fault of the AAG or the northeastern edge of the IA is an oblique-slip normal fault. Consequently, all of these field and seismic data reveal an extensional neotectonic regime through the northeast edge of the outer IA despite the previously reported compressional neotectonic regime. Isparta Ac›s›'n›n (GB Turkiye) KD D›fl Kenar›nda Genifllemeli Yenitektonik Rejim: Yeni Arazi ve Sismik Veriler Ozet: Akflehir-Afyon Grabeni (AAG) 4—20 km genifllikte, 130 km uzunlukta ve KB gidiflli, aktif bir cokuntu alan› olup, KD da yer alan orta Anadolu ve GB da yer alan Isparta Ac›s›'n› (IA) birbirinden ay›r›r. AAG'nin GB kenar›n› ve IA'n›n KD kenar›n› s›n›rlayan fay, daha once, s›k›flma turu bir yap› olarak yorumlanm›flt›r. Halbuki bizim arazi verilerimiz ve yeni sismik veriler, bu fay›n, genifllemeli yenitektonik rejimi karakterize eden verev at›ml› normal bir fay olduunu kan›tlam›flt›r. AAG aral›kl› (fas›lal›) ve bak›fl›ms›z bir geliflim tarihcesine sahiptir. Grabenin bu nitelii, ustuste gelmifl iki ayr› graben dolgusu ve grabenin kendine ozgu yap›s› ile belirginlik kazan›r. Daha yafll› olan graben dolgusu k›vr›ml› ve bindirme fayl› olup erken Orta Miyosen yafll›d›r. Daha genc olan graben dolgusu ise hemen hemen yatay konumlu olup s›k›flma turunde hic bir deformasyon gecirmemifltir. Pliyo-Kuvaterner yafll› olan graben dolgusu, daha yafll› olan graben dolgusu uzerinde ac›l› uyumsuzluk ile yer al›r. AAG'nin GB ve KD kenarlar›n› s›n›rlayan faylar (Akflehir ve Karagoztepe Ana Faylar›, AMF ve KMF) boyunca, Gec Pliyosen ve Erken Pliyostesen'den beri gercekleflmifl olan toplam dufley at›m miktarlar› s›rayla 870 m ve 200 m dir. Faylar uzerindeki devinimin tekduze olduu kabul edilirse, bu deerler, grabenin iki kenar› boyunca gercekleflen devinim h›z›n›n s›rayla 0.3 mm/y›l ve 0.2 mm/y›l olduunu ve AAG'nin bak›fl›ms›z niteliini ac›kca gosterir. Yuzeyde her iki ana fay (AMF ve KMF) duzleminden al›nan kayma verilerinin kinematik analizi, bu faylar uzerindeki devinimin, az miktarda sayanal dorultu bilefleni olan verev at›ml› bir devinim olduunu, ayr›ca genifllemenin de KD—GB dorultusunda gercekleflmekte olduunu gostermifltir. Arazi verileriyle elde edilen bu sonuc, 15 Aral›k 2000 Sultanda¤› (Mw=6.0) ve 3 fiubat 2002 Cay (Mw=6.5) depremlerinin odak mekanizmas›