Geomorphic and geological constraints on the active normal faulting of the Gediz (Alaşehir) Graben, Western Turkey

Abstract

The Gediz (Alaşehir) Graben is located in the highly tectonically active region of Western Turkey. Extension owing to regional geodynamic controls has resulted in a broadly two-phase evolution of the graben; first, low-angle normal faulting relating to the exhumation of the Menderes Massif metamorphic core complex took place between 16 and 2.6 Ma; second, high-angle normal faulting initiated c. 2 Ma forming the Gediz and other east–west-trending graben in the region. Here we quantify the throw rate along the fault array over the last 2.6, 2 and 0.7 myr using structural and geological constraints, along with analysis of topographic relief as a proxy for footwall uplift. We derive, for the first time, time-averaged rates of fault motion from 0.4 to 1.3 mm a −1 along the strike of the Gediz Graben, with variation in throw rate associated with the geometry of single fault strands. Patterns in throw rate along-strike of the graben-bounding fault array also suggest that the fault segments have become linked during the last 2.6–2 myr, possibly at 0.8–0.7 Ma. Furthermore, these data suggest that an earthquake occurring along the graben-bounding fault could have a maximum predicted M w of 6.3–7.6.