A Kinematic Rupture Generator for Ground-Motion Simulations: Validation and Scenarios in South Iceland

ABSTRACT

Physics-based ground-motion simulation can reduce epistemic uncertainty in regions with sparse strong-motion data, but hazard applications require fault rupture ensembles that are physically plausible, statistically controlled, and computationally efficient. We present a modular kinematic rupture generator for physics-based simulations (PBS) in which final slip, rupture speed ratio (VR/VS), and peak slip velocity (Vmax) are modeled as heterogeneous, mutually correlated spatial fields governed by prescribed one-point statistics and covariance-based two-point structure. The generator supports both event-constrained ruptures (for validation) and fully stochastic scenario ruptures, while enabling systematic propagation of source uncertainty through an effective stress-parameter scaling with Vmax. We demonstrate the approach using a regional three-dimensional numerical model of South Iceland (accurate up to 1.9 Hz) solved with the spectral-element code SPEED. A broadband extension is obtained via the artificial neural network to broadband (ANN2BB) method. Validation against the June 2000 moment magnitude (Mw) 6.5 and 6.4 earthquakes shows good agreement between recorded and simulated low-frequency waveforms and response spectra, supported by goodness-of-fit metrics across duration, peak measures, and long-period spectral ordinates. We then generate Mw 6.5 and Mw 7 scenario ensembles and compare their spectral-acceleration attenuation and variability with local and global ground-motion models. Mw 6.5 scenarios track the Icelandic model within its calibration range, whereas Mw 7 scenarios diverge from extrapolated local predictions, indicating substantial epistemic uncertainty in large-magnitude, short-distance scaling where observations are unavailable. The simulated variability is consistent with empirical expectations, supporting the use of the proposed rupture-generator–PBS framework to produce region-specific, nonergodic ground-motion ensembles for scenario-based risk analysis and PBS-informed hazard assessment.