Stratigraphic and Structural Evidence for Fault Reactivation: The Active Manisa Fault Zone, Western Anatolia

Authors: ÇAĞLAR ÖZKAYMAK, HASAN SÖZBİLİR

Abstract: In this paper, we aim to present stratigraphic and structural evidence for fault reactivation that is linked with evolution of the western part of the Manisa fault zone - a major range-bounding fault that is geomorphologically expressed as a trace of north-facing scarps bounding the southern margin of the Manisa basin which is subsidiary to the Gediz Graben. We identify that the Manisa fault zone, at its western end, consists of three fault segments which are en échelon arranged in left step. Each segment is identified as steep topographic scarps visible on topographic maps and in landsat images. Fault scarps range in height from a few metres to several hundred metres. Each segment is approximately 3 km long and display through-going zigzag trace with a total length of up to 10 km; the fault segments show evidence for linkage and breaching at the relay ramps. We interpret that such fault patterns are characteristic for regions experiencing extension where fault segments are reactivated pre-existing structures with an oblique sense of motion. The solid evidence comes from the presence of three sets of striations with different orientations on the fault segments. Where preserved, two variably oriented strike-slip slickenlines are overprinted by dip-slip striations. Kinematic analysis has also revealed a systematic variation in slip direction along the Manisa fault zone: while the motion along the central parts of the fault zone - as section oriented almost perpendicular to the regional extension direction - is almost pure dip-slip, substantial oblique-slip motion prevails near the fault tips. We therefore suggest that the Manisa fault zone is a reactivated structure with at least three different motions since the Miocene: (i) the earliest motion was sinistral and consistent with an E-W-trending contraction during the Miocene-Early Pliocene time interval; (ii) during the Plio-Quaternary, the Manisa fault zone was a dextral oblique-slip normal fault associated with NE-SW-trending extension; and (iii) the youngest configuration is represented by an almost dip-slip normal fault that is attributed to a NE-SW-trending extensional tectonic regime commenced by the Quaternary. We also speculate that extreme attention must be given to the palaeostress data on the fault surfaces and that many of the the E-W-trending normal faults in western Anatolia are in fact reactivated structures that formed under different stress regimes since the Miocene. The general orientation of these normal faults can therefore not be regarded as evidence to support N-S-trending extension.

Keywords: Manisa fault zone, active fault, relay ramp, reactivation, west Anatolia

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