Kinematics and Basin Formation Along the Ezinepazar-Sungurlu Fault Zone, NE Anatolia, Turkey

Authors: MEHMET KORHAN ERTURAÇ, OKAN TÜYSÜZ

Abstract: The Ezinepazar-Sungurlu Fault (EzSF) is a major offshoot of the dextral North Anatolian Fault (NAF) zone, which bifurcates from the main fault strand around the Niksar pull-apart basin (37°E) and strikes through the Central Anatolian Block for 200 km to the west (34°E). The easternmost segment of the EzSF, the Ezinepazar Fault (EzF), which ruptured during the 1939 Erzincan earthquake (Mw= 7.8), has a very remarkable expression as a single-strand fault. Micromammal dating of young sediments along this segment indicate that the EzF was initiated during the Middle Pleistocene (0.7-1 Ma) and propagated westward accumulating 6.5±0.5 km maximum morphological offset. The central segment of the EzSF, the Deliçay Fault (DF), is expressed as an en-échelon pattern and controlled the formation of a narrow fault-wedge basin (Aydınca Plain). The stepover between the DF and its western continuation, the Geldingen Fault (GF), forms a young pull-apart basin (Geldingen Basin) where the maximum morphological offset is measured at 3.5±1 km. In the westernmost part of the fault zone, the deformation zone widens and the EzSF bifurcates into the Mecitözü (MF) and the Sungurlu faults (SF). The MF controlled the deposition of continental clastics, dated as Late Miocene-Early Pliocene by using mammal chronology (MN13-14). The Neogene-Quaternary stratigraphy of the basins along the EzSF indicates two phases of faulting-related basin formation. The first period took part during the Late Miocene-Early Pliocene; the second phase started with the initiation of the EzF in the east during the Middle Pleistocene. The western propagation of the fault caused the reactivation of older tectonic lines as an element of the NAF system. The offset distribution measured along the EzSF shows that accumulated long-term slip is not uniform along the fault, as it decreases gradually where the fault becomes distant from the NAF main strand. This projection is applicable to present day slip rate distribution along the EzSF, which is shown also by GPS measurements and is therefore important for earthquake hazard estimates for the region.

Keywords: North Anatolian Fault, Ezinepazar-Sungurlu Fault, morphotectonics, splay faulting, Amasya Basin

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