From Interseismic Coupling to Ground Motions: An Empirical Amplitude and Phase Approach for Megathrust Earthquake Simulations

Time-dependent seismic hazard assessments require ground-motion models that capture source complexity, rupture timing, and the spatial variability of intensity measures, while remaining applicable to engineering practice. Here, we present a simulation framework that combines empirical models for the Effective Amplitude Spectrum (EAS) and the Group Delay Time (GDT) with physics-informed rupture scenarios to generate broadband ground-motion time histories for large interface earthquakes and potential future events based on interseismic coupling models. The empirical EAS and GDT models are derived from a curated strong-motion dataset from the Chilean subduction zone, encompassing relatively small events with magnitudes ranging from 4.6 to 7.0. To extend the approach to megathrust earthquakes, we adopt a rupture-decomposition strategy in which the total seismic moment is distributed among subevents with prescribed rupture and travel times. We first apply the framework to the 2010 Mw 8.8 Maule, 2014 Mw 8.1 Iquique, and 2015 Mw 8.3 Illapel earthquakes, using coseismic slip models and also interseismic coupling distributions, to examine whether coupling can serve as a proxy for earthquake ruptures. The observed-versus-predicted comparison of seismic intensities includes Fourier amplitudes, Arias intensity, pseudo-spectral acceleration ordinates, PGA, and PGV. Despite its relative simplicity, the approach reproduces the main amplitude and temporal characteristics of observed ground motions. Slip-based simulations tend to slightly overestimate shaking amplitudes, whereas coupling-based scenarios produce lower, more conservative ground motions while preserving realistic durations. Residual analyses show improved temporal coherence and spatial variability compared to commonly used predictive ground-motion models. In light of these results, we finally apply this approach to mature seismic gaps identified from geodetic coupling models along the Chilean margin, including the Atacama and Central Chile segments, last ruptured in 1922 (Mw~8.5) and 1730 (Mw~9.0), respectively. Simulations at virtual stations reveal high seismic intensities in densely populated cities such as Valparaíso and Santiago, underscoring the importance of integrating time-dependent exposure and vulnerability models to compute the seismic risk associated with the 1730-type scenario. These findings highlight the value of including coupling information into time-dependent ground-motion simulations and demonstrate how rupture timing and fault loading influence seismic hazard assessments. The proposed framework provides a physically consistent and engineering-relevant tool for seismic hazard analysis in subduction environments.