Asymmetric growth of strike-slip faults controlled by 3-D fault structure: Insights from the Mw 7.8 2023 Kahramanmaraş (Turkey) earthquake

The reactivation of deep-seated, throughgoing strike-slip faults produces highly segmented fault zones at shallower levels, yet how displacement is partitioned among segments as the fault grows remains poorly constrained. We address this by examining a ∼160-m-long section of the East Anatolian fault surface rupture of the Mw 7.8 2023 Kahramanmaraş strike-slip earthquake (Turkey). The rupture offsets meter-spaced ridges and furrows in a ploughed field, providing a unique opportunity for detailed displacement measurements, which were obtained from an orthophoto and a digital elevation model (DEM) built for this study. The surface rupture consists of ten primary segments separated by nine restraining stepovers and is associated with a 3-D strain field dominated by ∼3.5 m of left-lateral offset. Displacement patterns allow us to derive a new model for strike-slip fault growth in which deformation is asymmetric and controlled by the 3-D structure of the fault—specifically, by the position of the underlying fault relative to shallow fault segments. Initially, displacement is accommodated by contraction within restraining stepovers. With increasing displacement, fault segments located closer to the trace of the underlying fault consistently accumulate greater displacement. This asymmetry is facilitated by enhanced synthetic rotation within stepovers. With further displacement, the higher-displacement segment bounding a stepover becomes dominant, while the other one is bypassed and layer rotation ceases. These results not only improve fault growth models but could also inform seismic hazard models and impact industrial applications dealing with subsurface faulted reservoirs.