Unraveling Holocene surface-faulting history of the Çay segment, Sultandağı Fault (SSW Türkiye): linking paleoseismic evidence to segment-scale seismic behavior

Abstract The ~ 115 km long Sultandağı Fault forms the southern boundary of the Quaternary Afyon–Akşehir Graben in western Türkiye and represents a major active normal fault within the regional extensional regime. The Mw 6.5 Çay earthquake of 3 February 2002 produced surface rupture along its central segment, confirming its seismogenic capacity. This study presents the first detailed paleoseismological investigation of the Çay segment based on two trenches (Eskiköprü and Maltepe) excavated across faulted Holocene deposits. Stratigraphic and structural evidence documents five Holocene surface-rupturing earthquakes (E1–E5), including the historically documented 2002 Çay earthquake. Fourteen AMS radiocarbon samples (charcoal, bone, and carefully selected bulk organic sediments) were analyzed and modeled using a Bayesian approach in OxCal with stratigraphic constraints. Event ages and inter-event intervals were calculated at the 95.4% probability level (2σ), yielding millennial-scale recurrence behavior with uncertainty ranges extending up to ~ 1.59 kyr. The ~ 26 km cumulative surface rupture length observed during the 2002 earthquake corresponds to Mw ≈ 6.7 based on the Wells and Coppersmith (1994) normal-fault scaling relation, consistent with instrumental estimates. Measured vertical displacements (~ 20–25 cm) in trench exposures support moderate-magnitude (Mw 6–7) earthquake potential for single-segment ruptures. These results demonstrate repeated Holocene surface faulting with millennial recurrence intervals and confirm the capacity of the Çay segment to generate Mw ≥ 6.5 earthquakes. The findings provide quantitative input for time-dependent seismic hazard assessment within the Akşehir-Simav extensional system.