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1. Linked and fully-coupled 3D earthquake dynamic rupture and tsunami modeling for the Húsavík-Flatey Fault Zone in North Iceland

   Kutschera, F; Gabriel, A-A; Wirp, SA; Li, B; Ulrich, T; Abril, C; Halldórsson, B (February 2024, Solid earth)

   Tsunamigenic earthquakes pose considerable risks, both economically and socially, yet earthquake and tsunami hazard assessments are typically conducted separately. Earthquakes associated with unexpected tsunamis, such as the 2018 Mw  7.5 strike-slip Sulawesi earthquake, emphasize the need to study the tsunami potential of active submarine faults in different tectonic settings. Here, we investigate physics-based scenarios combining simulations of 3D earthquake dynamic rupture and seismic wave propagation with tsunami generation and propagation. We present time-dependent modeling of one-way linked and 3D fully coupled earthquakes and tsunamis for the ∼ 100 km long Húsavík–Flatey Fault Zone (HFFZ) in North Iceland. Our analysis shows that the HFFZ has the potential to generate sizable tsunamis. The six dynamic rupture models sourcing our tsunami scenarios vary regarding hypocenter location, spatiotemporal evolution, fault slip, and fault structure complexity but coincide with historical earthquake magnitudes. Earthquake dynamic rupture scenarios on a less segmented fault system, particularly with a hypocenter location in the eastern part of the fault system, have a larger potential for local tsunami generation. Here, dynamically evolving large shallow fault slip (∼ 8 m), near-surface rake rotation (± 20∘), and significant coseismic vertical displacements of the local bathymetry (± 1 m) facilitate strike-slip faulting tsunami generation. We model tsunami crest to trough differences (total wave heights) of up to ∼ 0.9 m near the town Ólafsfjörður. In contrast, none of our scenarios endanger the town of Akureyri, which is shielded by multiple reflections within the narrow Eyjafjörður bay and by Hrísey island. We compare the modeled one-way linked tsunami waveforms with simulation results using a 3D fully coupled approach. We find good agreement in the tsunami arrival times and location of maximum tsunami heights. While seismic waves result in transient motions of the sea surface and affect the ocean response, they do not appear to contribute to tsunami generation. However, complex source effects arise in the fully coupled simulations, such as tsunami dispersion effects and the complex superposition of seismic and acoustic waves within the shallow continental shelf of North Iceland. We find that the vertical velocity amplitudes of near-source acoustic waves are unexpectedly high – larger than those corresponding to the actual tsunami – which may serve as a rapid indicator of surface dynamic rupture. Our results have important implications for understanding the tsunamigenic potential of strike-slip fault systems worldwide and the coseismic acoustic wave excitation during tsunami generation and may help to inform future tsunami early warning systems. 

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2. Hellenic Arc tsunami generation from M W 8+ 3-D margin-wide dynamic rupture earthquake scenarios

   https://doi.org/10.1093/gji/ggag181  

   Wirp, S A; Kutschera, F; Ulrich, T; Bader, M; Lorito, S; Gabriel, A -A (July 2026, Geophysical Journal International)

   SUMMARY The Hellenic Arc Subduction Zone is the most seismically active region in the Mediterranean, capable of generating large earthquakes and tsunami. Given the proximity of densely populated coastlines, understanding the characteristics of potential future large tsunamigenic earthquakes is crucial for assessing tsunami hazard. We present nonlinear shallow water tsunami simulations sourced from the static seafloor displacements of five $$M_{\rm W}$$ 8–9 dynamic rupture earthquake scenarios along the Hellenic Arc, varying in hypocentral location, rupture extent and moment magnitude. Our results show that shallow slip and off-fault plastic deformation control the vertical near-trench uplift, tsunami height, and tsunami arrival time, particularly towards the south-west of the Hellenic Arc. Plasticity increases the tsunami amplitudes by over 50 percent. Maximum tsunami amplitudes reach up to 6.6 m near central and eastern Mediterranean coastlines, while the northern Aegean and the western Mediterranean remain mostly shielded by landmasses in all scenarios. We use the time-dependent seafloor deformation of the worst-case scenario among those considered to highlight differences between static and time-dependent sourcing for tsunami modelling. The results show up to 12 percent higher maximum wave heights in the near-field and slightly lower tsunamis in the far-field compared to a static sourcing, while the waves arrive later. The same scenario is further extended to a large-scale, fully coupled 3-D earthquake-tsunami model that captures dynamic rupture, seismic and acoustic wave propagation, and time-dependent tsunami generation. The fully coupled simulation reveals complex interactions between acoustic and tsunami waves during the early generation phase, including dispersion and wave conversions between seismic and ocean-acoustic waves, which static or linked models do not capture. Overall, our results provide quantitative evidence that source complexity, both spatial and temporal, affects tsunami near–field amplitudes, far–field decay, and arrival metrics, with important implications for physics–based tsunami hazard assessment along the Libyan and Egyptian coasts, the southern Aegean, and eastern Mediterranean shorelines. These results also highlight the value of integrating 3-D dynamic rupture modelling with tsunami simulations and enhance our understanding of tsunami generation mechanisms. 

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3. Dynamic Rupture Modeling of Large Earthquake Scenarios at the Hellenic Arc Toward Physics‐Based Seismic and Tsunami Hazard Assessment

   https://doi.org/10.1029/2024JB029320  

   Wirp, Sara Aniko; Gabriel, Alice‐Agnes; Ulrich, Thomas; Lorito, Stefano (November 2024, Journal of Geophysical Research: Solid Earth)

   Abstract The Mediterranean Hellenic Arc subduction zone (HASZ) has generated several 8 earthquakes and tsunamis. Seismic‐probabilistic tsunami hazard assessment typically utilizes uniform or stochastic earthquake models, which may not represent dynamic rupture and tsunami generation complexity. We present an ensemble of ten 3D dynamic rupture earthquake scenarios for the HASZ, utilizing a realistic slab geometry. Our simplest models use uniform along‐arc pre‐stresses or a single circular initial stress asperity. We then introduce progressively more complex models varying initial shear stress along‐arc, multiple asperities based on scale‐dependent critical slip weakening distance, and a most complex model blending all aforementioned heterogeneities. Thereby, regional initial conditions are constrained without relying on detailed geodetic locking models. Varying epicentral locations in the simplest, homogeneous model leads to different rupture speeds and moment magnitudes. We observe dynamic fault slip penetrating the shallow slip‐strengthening region and affecting seafloor uplift. Off‐fault plastic deformation can double vertical seafloor uplift. A single‐asperity model generates a 8 scenario resembling the 1303 Crete earthquake. Using along‐strike varying initial stresses results in 8.0–8.5 dynamic rupture scenarios with diverse slip rates and uplift patterns. The model with the most heterogeneous initial conditions yields a 7.5 scenario. Dynamic rupture complexity in prestress and fracture energy tends to lower earthquake magnitude but enhances tsunamigenic displacements. Our results offer insights into the dynamics of potential large Hellenic Arc megathrust earthquakes and may inform future physics‐based joint seismic and tsunami hazard assessments. 

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4. Anatomy of strike-slip fault tsunami genesis

   https://doi.org/10.1073/pnas.2025632118  

   Elbanna, Ahmed; Abdelmeguid, Mohamed; Ma, Xiao; Amlani, Faisal; Bhat, Harsha S; Synolakis, Costas; Rosakis, Ares J (May 2021, Proceedings of the National Academy of Sciences)

   Tsunami generation from earthquake-induced seafloor deformations has long been recognized as a major hazard to coastal areas. Strike-slip faulting has generally been considered insufficient for triggering large tsunamis, except through the generation of submarine landslides. Herein, we demonstrate that ground motions due to strike-slip earthquakes can contribute to the generation of large tsunamis (>1 m), under rather generic conditions. To this end, we developed a computational framework that integrates models for earthquake rupture dynamics with models of tsunami generation and propagation. The three-dimensional time-dependent vertical and horizontal ground motions from spontaneous dynamic rupture models are used to drive boundary motions in the tsunami model. Our results suggest that supershear ruptures propagating along strike-slip faults, traversing narrow and shallow bays, are prime candidates for tsunami generation. We show that dynamic focusing and the large horizontal displacements, characteristic of strike-slip earthquakes on long faults, are critical drivers for the tsunami hazard. These findings point to intrinsic mechanisms for sizable tsunami generation by strike-slip faulting, which do not require complex seismic sources, landslides, or complicated bathymetry. Furthermore, our model identifies three distinct phases in the tsunamic motion, an instantaneous dynamic phase, a lagging coseismic phase, and a postseismic phase, each of which may affect coastal areas differently. We conclude that near-source tsunami hazards and risk from strike-slip faulting need to be re-evaluated. 

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5. Dynamic restrengthening and fault heterogeneity explain megathrust earthquake complexity

   https://doi.org/10.1038/s41467-026-71722-3  

   Wong, Jeremy_Wing Ching; Gabriel, Alice-Agnes; Fan, Wenyuan (April 2026, Nature Communications)

   Abstract Megathrusts host Earth’s largest earthquakes. Understanding the physical conditions controlling their rupture dynamics is critical for assessing seismic and tsunami hazards. These earthquakes often display complex rupture dynamics, exemplified by the 2011 Tohoku-Oki earthquake, which exhibited multiple rupture episodes, depth-dependent seismic radiation, and substantial tsunamigenic slip near the trench. However, how such complexity arises from preexisting physical conditions remains uncertain. Here, we demonstrate that the observed rupture complexity of the Tohoku-Oki earthquake can spontaneously and self-consistently emerge, driven by rapid coseismic frictional restrengthening and data-informed fault heterogeneity. We use an ensemble of 3D dynamic rupture simulations to identify that mixed downdip pulse-like and updip crack-like rupture are driven by dynamic stress redistribution with episodic rupture reactivation. By featuring low fault strength compared to its dynamic stress drop, a preferred model can consistently reproduce the observed complex depth-dependent propagation speeds, multiple rupture fronts as imaged by back-projection, and large tsunamigenic slip at the trench. Our findings demonstrate that preexisting fault heterogeneity conjointly with dynamic frictional weakening and restrengthening drives seemingly unexpected megathrust rupture complexity, highlighting the need to include dynamic effects into physics-based seismic and tsunami hazard assessments of future earthquakes. 

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