3D Dynamic Rupture Modeling of the 6 February 2023, Kahramanmaras, Turkey Mw 7.8 and 7.7 Earthquake Doublet Using Early Observations

The 2023 Turkey earthquake sequence involved unexpected ruptures across numerous fault segments. We present 3D dynamic rupture simulations to illuminate the complex dynamics of the earthquake doublet. Our models are constrained by observations available within days of the sequence and deliver timely, mechanically consistent explanations of the unforeseen rupture paths, diverse rupture speeds, multiple slip episodes, heterogeneous fault offsets, locally strong shaking, and fault system interactions. Our simulations link both earthquakes, matching geodetic and seismic observations and reconciling regional seismotectonics, rupture dynamics, and ground motions of a fault system represented by 10 curved dipping segments and embedded in a heterogeneous stress field. The first, Mw 7.8 earthquake features delayed backward branching from a steeply branching splay fault, not requiring supershear speeds. The asymmetrical dynamics of the distinct, bilateral second Mw 7.7 earthquake are explained by heterogeneous fault strength, prestress orientation, fracture energy, and static stress changes from the previous earthquake. Our models explain the northward deviation of its eastern rupture and the minimal slip observed on the Srg fault. 3D dynamic rupture scenarios can elucidate unexpected observations shortly after major earthquakes, providing timely insights for data-driven analysis and hazard assessment toward a comprehensive, physically consistent understanding of the mechanics of multifault systems. Our models illustrate the predisposition of complex fault geometries, prevalent in tectonically complex immature fault systems, for cascading multi-fault and multi-event earthquake sequences. The unexpected doublet dynamics maybe explained by stress and strength heterogeneity, and include branching and delayed triggering in backward direction; triggered high-stress drop events, a single fault system with variable relative strength hosting rupture propagating at highly variable rupture speeds across different segments and in different directions.