GEOSITES > The Gediz Graben

The Gediz Graben

Western Anatolia forms one of the most seismically active and rapidly extending regions in the world. It is currently experiencing an approximately N- S continental extension, at a rate of 30-40 mm year. It forms a part of the “Aegean Extensional Province”, a region of distributed extension that covers parts of Greece, Macedonia, Bulgaria and Albania. The approximately E. – W. trending grabens (e.g. Edremit, Bakırçay, Kütahya, Simav, Gediz, Küçük Menderes, Büyük Menderes, and Gokovagrabens) and their basin-bounding, active normal faults are the most prominent neo-tectonic features of Western Turkey. The activity of the basin bounding faults is shown from the numerous historical earthquakes. The cause and origin of the crustal extension of the Aegean Extensional Province has been debated at length, and proposals form four different models: (I) The ‘Tectonic escape’ model: (2) The ‘Back-arc spreading’ model: (3) The ‘Orogenic collapse’ model: (4) The ‘Episodic’: this being a two-stage graben model that involves a Miocene-Early Pliocene first stage (orogenic collapse), and a Plio-Quaternary second phase (the westward escape of the Anatolian block) of a N. – S. extension. The age of the grabens is also controversial and the proposals fall into three major categories: (I) The grabens began to form during the Tortonian. (2) The basins started to form during the Early Miocene and have continued their evolution since then. (3) The grabens are Plio-Quaternary structures.


The Gediz Graben is one of the grabens formed due to the tectonic movements in the region. It is thought that this graben began to form in consequence of the formation of the Karadut fault which is a separation fault. There are listric faults to either side of the graben which have caused the graben to intermittently collapse. From the mountainous areas towards the plain the age of these faults become younger. The difference in height between the base of the graben and the highest part of the Bozdag Mountains is about 2000 meters. This difference in elevationis remarkable, clearly indicating the severity of the tectonic movements in the neo-tectonic period.

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