Physics-based dynamic rupture models, fault interaction and ground
motion simulations for the segmented Húsavík-Flatey Fault Zone, Northern
Iceland
Abstract
We present 3-D spontaneous dynamic rupture earthquake scenarios for the
Húsavík–Flatey Fault Zone (HFFZ) in Northern Iceland. We construct
three fault system models consisting of up to 55 segments of varying
geometric complexity. By varying hypocenter locations, we analyze
rupture dynamics, fault interactions and their associated ground motions
and observational uncertainties in 79 scenarios. We use regional
observations to constrain 3-D subsurface velocities and viscoelastic
attenuation as well as fault stress and strength. Our models account for
topo-bathymetry, off-fault plasticity and we explore the effect of fault
roughness. Our spontaneous dynamic rupture scenarios can match historic
magnitudes. We show that the fault system segmentation and geometry,
hypocenter locations, initial stress conditions and fault roughness have
strong effects on multi-fault rupture dynamics across the HFFZ. Breaking
of different portions of the same fault system leads to varying rupture
dynamics, slip distributions and magnitudes. All dynamic rupture
scenarios yield highly heterogeneous near-field ground motions. We
observe amplification from rupture directivity, geometric complexities,
and amplification and shielding due to topography. We recover a
magnitude-consistent attenuation relationship in good agreement with new
regional empirical ground motion models. Physics-based ground motion
variability changes with distance and increases for unilateral vs.
bilateral rupture. Our study illustrates important ingredients for fully
physics-based, regional earthquake scenarios, their respective
importance for rupture dynamics and ground motion modeling and how they
can be observationally constrained and verified. We entail that dynamic
rupture scenarios can be useful for non-ergodic probabilistic seismic
hazard assessment, specifically in data-limited regions.