Identification of a previously unrecognized listric fault beneath the Acıpayam Graben: Insights from integrated DInSAR and field observations

The 20 March 2019 Acıpayam earthquake (Mw 5.7) offers a valuable opportunity to examine the complex seismotectonic behavior of the Fethiye-Burdur Fault Zone (FBFZ), a transtensional structure in southwestern Türkiye. This study integrates field observations and focal mechanism data with differential interferometric synthetic aperture radar (DInSAR) analysis to reassess the geometry of the causative fault. In contrast to previously proposed northeast-dipping blind fault models, the data obtained in this study indicate a southwest-dipping listric normal-fault system centered on the Yeniköy Fault, projecting beneath alluvial cover. Vertical displacement maps from Sentinel-1 show coseismic subsidence up to 5.8 cm and broader postseismic deformation. The deformation asymmetry, surface cracks, vertical displacement zones, and morphotectonic lineaments collectively support the continuity of a shallow fault. Aftershock patterns and kinematic indicators corroborate the activation of a segmented fault network, while the deformation field highlights the roles of stress transfer and viscoelastic relaxation in shaping postseismic responses. Additionally, historical seismicity suggests a recurrence interval of approximately 122 years for destructive events, whereas previous paleoseismological studies identify three Holocene surface ruptures with an average recurrence of about 350 years, highlighting both short- and long-term earthquake cycles. The 2019 rupture may reflect strain transfer from the most recent paleo-event to adjacent segments, reinforcing the seismogenic significance of the Yeniköy fault despite the absence of a clear surface rupture. DInSAR-derived deformation and focal mechanism patterns align with a steeply dipping listric normal-fault whose curvature explains the lack of a clear surface trace. These findings underscore the importance of integrating geodetic, field-based, and historical perspectives to refine seismic hazard assessments in Acıpayam and comparable extensional settings.