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

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.

Earthquake-generated tsunamis are generally associated with large submarine events on dip-slip faults, in particular at subduction zone megathrust interfaces

Overview of the Tjörnes Fracture Zone (TFZ), which connects the Kolbeinsey Ridge (KR) as part of the Mid-Atlantic Ridge offshore north of Iceland (Eyjafjarðaráll Rift Zone) to its manifestation on land in the Northern Volcanic Zone (NVZ). Yellow circles represent relocated seismicity from 1993 to 2019

Here, we focus on the

North Iceland has experienced several large earthquakes in the past. Two magnitude

A better understanding of the complex interaction between static and time-dependent earthquake displacements, off-fault deformation, and seismic, acoustic, and tsunami amplitudes is now possible, using realistic 3D scenarios. Non-linear earthquake dynamic rupture simulations combining coseismic frictional failure on prescribed faults and seismic wave propagation are powerful tools to investigate earthquake dynamics as a consequence of the model's initial conditions

In this study, we investigate the tsunami potential of the HFFZ using two techniques to couple earthquake and tsunami models. First, we apply a one-way linked approach that links the time-dependent seafloor deformation from 3D earthquake dynamic rupture with a subsequent tsunami simulation based on solving the shallow-water equations

Overview over the six 3D dynamic rupture earthquake scenarios based on

We detail the earthquake and tsunami model setups in Sect.

We present one-way linked (see Sect.

We use six earthquake scenarios based on a suite of 3D spontaneous dynamic rupture simulations developed in

The fault geometry plays an important role in the potential for tsunami generation caused by submarine earthquake rupture. Fault trenching has been conducted for the onshore part of the HFFZ

Summary of dynamic rupture parameters chosen by

Following

The stress shape ratio

The dynamic rupture models use a linear slip-weakening (LSW) friction law with frictional cohesion to model frictional yielding and dynamic slip evolution

The relative fault strength is expressed by the maximum pre-stress ratio

The inferred locking depth for the HFFZ is 6 to 10 km

All dynamic rupture models incorporate off-fault plasticity (Fig.

We use the scientific open-source software package SeisSol (

The one-way linked workflow uses the time-dependent seafloor displacement output from SeisSol to initialize sea surface perturbations within

Traditional earthquake–tsunami modeling is often based on two-step approaches

Based on the six scenarios using the one-way linked approach, we analyze the three plausible “worst-case” tsunamigenic scenarios on the simpler fault geometry with the fully coupled approach, Simple-West, Simple-Middle, and Simple-East. All initial conditions of the dynamic rupture models are kept the same as in the respective linked scenarios.

Moment release rates for the six earthquake dynamic rupture (DR) simulations (up to

Key results of our six earthquake dynamic rupture scenarios. Note that we only report the maximum offshore coseismic vertical displacements (i.e., seafloor offsets) in the table because the onshore vertical displacements do not contribute to the tsunami generation.

The earthquake dynamic rupture scenarios with nucleation in the west and east of the complex fault geometry yield a significantly smaller moment magnitude than the other four scenarios, which is reflected in the moment rates (Fig.

Uplift and subsidence from the surface displacements of earthquake dynamic rupture simulations after accounting for local bathymetry using the Tanioka filter

The coseismic earthquake displacements reach up to

While the maximal coseismic seafloor subsidence of the simulation Complex-Middle is equivalent in size to the maximum subsidence observed for the scenarios on the simpler fault geometry, the rupture generates only half as much uplift (Table

Dynamic rake rotation in the dynamic rupture simulations on

Earthquakes on a vertically dipping, right-lateral fault system, such as the HFFZ, predominantly exhibit rake angles of 180

The coastline of North Iceland includes several smaller islands, like Flatey, Grímsey, and Hrísey island (Fig.

Sea surface height anomaly (ssha) of all six one-way linked earthquake–tsunami scenarios at 10

We define the sea surface height anomaly (ssha) as the deviation from the ocean surface at rest. We place six synthetic tide gauge stations offshore, in direct proximity to the towns of Húsavík, Akureyri, Dalvík, Ólafsfjörður, Siglufjörður, and Grímsey island. Every tsunami is simulated for 40

We show snapshots of tsunami propagation after 120

Sea surface height anomaly (ssha;

Maximum sea surface height anomaly (ssha;

We first analyze the three one-way-linked tsunami scenarios sourced by dynamic rupture simulations on the simpler fault geometry which cause overall larger wave heights. All dynamic ruptures on the simpler fault geometry are still propagating after 10

The initiating tsunami wavefronts from scenarios Simple-East and Simple-Middle evolve similarly, as seen in the snapshots at 2

Overall, the tsunami scenarios initiated by dynamic rupture scenarios on the complex fault geometry cause smaller tsunamis (Fig.

The tsunami scenario caused by dynamic rupture in the middle of the complex Húsavík–Flatey Fault, in scenario Complex-Middle, affects the town of Húsavík within the first minute. Wave heights reach

The 3D fully coupled earthquake–tsunami scenario Simple-East, with dynamic rupture on the simple fault geometry and a hypocenter in the east (yellow star). Snapshots at

Based on the results from the one-way linked simulations, we select those earthquake–tsunami scenarios causing larger wave heights for the computationally more demanding fully coupled models. A single fully coupled simulation of joint dynamic rupture and tsunami generation (for 3

First, we see the propagation of the tsunami at a speed of

Second, we observe the complex seismo-acoustic wave excitation and interaction in the initial phase of tsunami generation. The high-amplitude acoustic waves are clearly visible in all three scenarios. The seismic-generated acoustic waves propagate at a speed of

Next to ocean acoustic waves, we observe normal dispersion, i.e., frequency-dependent wave speeds, of the tsunami (Fig.

Submarine ruptures across strike-slip fault systems were long assumed to produce only minor vertical offsets and hence no significant disturbance of the water column. Linked and fully coupled earthquake dynamic rupture and tsunami modeling for the 2018

Our earthquake dynamic rupture scenarios can generate enough vertical seafloor displacements to source a localized tsunami. The scenarios on the simpler fault geometry may be considered worst-case events because the ruptures break over the entire main fault length, accumulating large fault slip (equivalent to

For all scenarios, we observe pronounced dynamic rake rotation near the surface, which we consider to be a plausible dynamic mechanism for generating increased coseismic vertical offset. The dynamic deviations from pure right-lateral strike-slip faulting are on the order of

In contrast to the suggested important contribution of off-fault deformation to strike-slip tsunami generation in Palu Bay

Modeling tsunami scenarios for hazard assessment or rapidly after submarine earthquakes often relies on simplifications, such as the negligence of source time-dependency, only considering vertical seafloor deformation without bathymetry effects, solely planar fault geometries, or neglecting tsunami dispersion and acoustic wave effects.

Non-dimensional parameters for the justification of modeling assumptions as introduced by

We see that the shallow water limit is fulfilled (

From the average water depth

In our study, we compare a simple fault geometry representing the Húsavík–Flatey Fault Zone and a very complex fault network consisting of 55 individual fault segments.

The three tsunami scenarios sourced by dynamic rupture simulations across the complex fault geometry cause significantly smaller tsunamis. This is due to lower and more segmented fault slip, leading to less vertical seafloor displacements which are spatially more restricted. The largest total wave height (i.e., crest to trough difference) of

We find that our scenario Simple-East poses the largest impact for coastal communities, except for Húsavík. Here the hypocenter is near the town, which may experience strong ground shaking

These differences may be due to our dynamic rupture models including dynamically evolving relatively large shallow fault slip (up to

We extend recent 3D dynamic rupture models by

Our simulated maximum fault slip occurring within the shallow offshore part of the HFFZ, i.e., the part which is relevant for the subsequent tsunami generation, is comparable to geological observations from earthquakes rupturing along faults with similar length to the HFFZ. Examples of strike-slip ruptures as summarized by

We exclude inundation in the one-way linked approach to enable a more meaningful comparison with the fully coupled method. Our fully coupled simulations are computationally demanding and do not allow us to model inundation

Our 3D fully coupled simulations include unexpectedly high-amplitude acoustic waves, which may serve as a rapid indicator of surface dynamic rupture. A better understanding of such acoustic wave signals may improve tsunami early warning, since these can be detected earlier in the far-field, e.g., at ocean-bottom pressure sensors, in comparison to the tsunami recorded at conventional DART buoys

We present a suite of realistic earthquake–tsunami scenarios for North Iceland, comparing one-way linked and 3D fully coupled modeling techniques. Both approaches agree in the resulting tsunamis from strike-slip earthquake dynamic rupture scenarios on the Húsavík–Flatey Fault Zone. We investigate two distinct fault system geometries – a simpler fault geometry with three fault segments and a highly complex fault system composed of 55 fault segments – to represent the 100

Accumulation of off-fault plastic strain (

Accumulated fault slip of the earthquake dynamic rupture simulations on

Normalized cumulative slip with depth for all six earthquake dynamic ruptures. The amount of shallow slip deficit (SSD) is indicated at the top left for each model on the respective fault geometry. In total, 0 % of SSD represents no near-surface reduction in the fault slip, while a higher percentage indicates that coseismic slip in the uppermost crust is less than the slip occurring at average depths of the seismogenic layer (i.e., 4–6

Sea surface height anomaly (ssha;

Waveform comparison for scenario Simple-East.

The 3D fully coupled earthquake–tsunami scenario Simple-Middle, with dynamic rupture on the simple fault geometry and a hypocenter in the middle (yellow star). Snapshots at

The 3D fully coupled earthquake–tsunami scenario Simple-West, with dynamic rupture on the simple fault geometry and a hypocenter in the west (yellow star). Snapshots at

Sea surface height anomaly (ssha;

SeisSol is available from GitHub (

Supplementary videos showing the propagation of the rupture front together with the seismic wave field spreading across the surface are available (

FK performed the formal analysis and used the dynamic rupture (DR) models provided by BL for earthquake–tsunami modeling. FK proceeded with the visualization and writing of the original draft. AAG supervised the project and gave substantial feedback for conceptualizing the research goals. SW and TU helped in the tsunami model setup and provided their expertise in post-processing earthquake–tsunami simulations. CA provided the data set of relocated seismicity up to 2019, the 3D velocity model for TFZ, and the simplified fault geometry on the basis of her analyses. Both AAG and BH acquired financial support. BH further supervised the work done at IMO. AAG, BL, SW, TU, and BH all provided comments on the article and helped to review and edit the original draft. Each author contributed to the article and approved the submitted version.

The contact author has declared that none of the authors has any competing interests.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors.

This article is part of the special issue “(D)rifting into the future: the relevance of rifts and divergent margins in the 21st century”. It is not associated with a conference.

We thank Lukas Krenz, Lauren Abrahams, and Eric Dunham for invaluable discussions and their contributions to the 3D fully coupled earthquake–tsunami modeling capabilities in SeisSol. We thank all participants of the NorthQuake 2022 workshop (

This work received funding from the European Union's Horizon 2020 research and innovation programme (TEAR ERC Starting; grant no. 852992) and Horizon Europe (ChEESE-2P, grant no. 101093038; DT-GEO, grant no. 101058129; and Geo-INQUIRE, grant no. 101058518). We acknowledge additional funding from the National Science Foundation (grant no. EAR-2121666) and the National Aeronautics and Space Administration (grant no. 80NSSC20K0495).

This paper was edited by Jordan J. J. Phethean and reviewed by two anonymous referees.