Active tectonics and seismicity of the Manisa Basin, Western Anatolia, Turkey

The Manisa Basin, forming a connection with the Gediz Graben, has a two-stage basin evolution, distinguished by an ancient and modern graben fill. The ancient basin-fill is made up of a folded and normal-to-reverse faulted and strike-slip-faulted Miocene volcano-sedimentary sequence. The younger modern basin-fill is represented by the early-middle Pleistocene continental clastics of the Turgutlu Formation, Quaternary Bahadır Alloformation comprising fluvial deposits, alluvial/colluvial sediments of late Pleistocene-early Holocene Emlakdere Alloformation, and alluvial-fluvial sediments of Holocene Manisa Alloformation. Structural and stratigraphical data reveal that the basin was initially formed as a lacustrine basin bounded by a volcanic ridge from the west; it was subsequently uplifted and deformed probably as a result of Pliocene wrench-dominated strike-slip tectonics. Post-Miocene strike-slip faulting along the İzmir Balıkesir Transfer Zone (İBTZ) occured along a right-lateral shear zone in the Manisa Basin. This suggests that some branches of the right-lateral movement of the North Anatolia Fault continues into the West Anatolian Extensional Province (WAEP). The youngest stage shows an NE?SW trending extension-dominated transtension. Modern graben fill forming under the control of the youngest stage is bounded by NE-trending strike-slip fault zone to the west and E?W-trending Manisa Fault Zone (MFZ) to the south. MFZ comprises three major seismogenic zones; western, central and eastern sectors providing minimum slip rates of 0,1, 0,3 and 0,26 mm/year, respectively. Tectonic geomorphology studies and computed geomorphic indices along three sectors suggest that the analyzed normal fault segments are linear and highly active. On the western sector of the MFZ, we performed trenching studies and find evidence for three palaeoearthquakes which correspond to 926 AD, 1595 or 1664 AD, with the most recent event in 1845 AD. The results suggest that the earthquake risk assessment for Manisa area is primarily essential.