Rupture dynamics and velocity structure effects on ground motion during the 2023 Türkiye earthquake doublet

Earthquake doublets defy typical aftershock patterns, challenging seismic hazard assessment. Understanding their rupture dynamics and interactions is crucial for advancing earthquake forecasting and hazard analysis. The destructive February 6, 2023, earthquake doublet of magnitudes 7.8 and 7.6 rocked south-central Türkiye and northwestern Syria. Here, we investigate ground motion characteristics through dynamic rupture modeling, revealing intricate rupture evolution driven by a 3D complex fault system and a rotational stress regime. Our models, validated by interferometric synthetic aperture radar, global navigation satellite system, local strong motion, and teleseismic data, reliably reproduce the observed shaking. Synthetic ground motions show directivity-driven amplification during subshear rupture, whereas supershear rupture elevates ground-motion levels off the fault but mitigates directivity amplification. Ground-shaking patterns are further affected by 3D Earth structure and topographic effects, and exhibit distance-decaying peak-ground velocity (1 Hz resolution) consistent with observations and empirical expectations. Our results highlight the value of integrating physics-based rupture simulations to enhance seismic hazard assessment. Dynamic rupture modeling suggests that heterogeneous seismic velocity structure increased ground motion, with off-fault shaking intensified by supershear rupture and strong directivity amplification generated by subshear rupture.