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Fault‐damage zones comprise multiscale fracture networks that may slip dynamically and interact with the main fault during earthquake rupture. Using 3D dynamic rupture simulations and scale‐dependent fracture energy, we examine dynamic interactions of more than 800 intersecting multiscale fractures surrounding a listric fault, emulating a major listric fault and its damage zone. We investigate 10 distinct orientations of maximum horizontal stress, probing the conditions necessary for sustained slip within the fracture network or activating the main fault. Additionally, we assess the feasibility of nucleating dynamic rupture earthquake cascades from a distant fracture and investigate the sensitivity of fracture network cascading rupture to the effective normal stress level. We model either pure cascades or main fault rupture with limited off‐fault slip. We find that cascading ruptures within the fracture network are dynamically feasible under certain conditions, including: (a) the fracture energy scales with fracture and fault size, (b) favorable relative pre‐stress of fractures within the ambient stress field, and (c) close proximity of fractures. We find that cascading rupture within the fracture network discourages rupture on the main fault. Our simulations suggest that fractures with favorable relative pre‐stress, embedded within a fault damage zone, may lead to cascading earthquake rupture that shadows main fault slip. We find that such off‐fault events may reach moment magnitudes up to Mw ≈ 5.5, comparable to magnitudes that can be otherwise hosted by the main fault. Our findings offer insights into physical processes governing cascading earthquake dynamic rupture within multiscale fracture networks. Plain Language Summary: Large geological faults are surrounded by many small fractures of different sizes and orientations, forming a fracture network around the main fault. The characteristics of an earthquake and its size may depend on the orientation of the main fault (and surrounding fractures) within the ambient stress field. Can a small (initial) rupture within a fracture network start a domino‐like (cascading) earthquake across the entire fault network? How does the compounded earthquake process depend on fracture orientation, local stress, and rupture starting point? To address these questions, we study earthquake rupture physics in a complex fault‐zone model comprising over 800 multiscale fracture planes surrounding a main fault. Using 3D dynamic rupture simulations and supercomputing, we explore how different ambient stress orientations, earthquake hypocenters, and levels of fault loading affect earthquake dynamics in fracture networks. The simulations demonstrate that cascading rupture in a fault zone is possible under certain conditions. Our results provide important insights into the physics of cascading earthquakes in multiscale fracture systems and hence are useful for advancing seismic hazard assessment for both natural and induced earthquakes. Key Points: We perform 3D dynamic rupture simulations in a network of >800 fractures and a listric main fault, assuming scale‐dependent fracture energyCascading rupture is possible under high fracture connectivity if a subset of fractures is favorable with respect to the ambient stressWe demonstrate the feasibility of dynamic rupture cascade irrespective of hypocenter locations within the fracture network [ABSTRACT FROM AUTHOR]

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 Mw7.5 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. [ABSTRACT FROM AUTHOR]

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 3D earthquake dynamic rupture with tsunami generation and propagation for the ~100 km long Húsavík-Flatey Fault Zone in North Iceland using time-dependent one-way linked and 3D fully-coupled earthquake-tsunami modeling. Our analysis shows that the HFFZ has the potential to generate sizeable tsunamis. The six dynamic rupture models sourcing our tsunami scenarios vary regarding hypocenter location, spatio-temporal evolution, fault slip, and fault structure complexity but coincide with historical earthquake magnitudes. We find that the 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 Ölafsfjöröur. In contrast, none of our scenarios endanger the town of Akureyri, which is shielded by multiple reflections within the narrow Eyjafjöröur 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 complex superposition of seismic and acoustic waves within the shallow continental shelf of North Iceland. We find that the vertical velocities 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 co-seismic acoustic wave excitation during tsunami generation and may help to inform future tsunami early warning systems. [ABSTRACT FROM AUTHOR]

The Húsavík‐Flatey Fault Zone (HFFZ) is the largest strike‐slip fault in Iceland and poses a high seismic risk to coastal communities. To investigate physics‐based constraints on earthquake hazards, we construct three fault system models of varying geometric complexity and model 79 3‐D multi‐fault dynamic rupture scenarios in the HFFZ. By assuming a simple regional prestress and varying hypocenter locations, we analyze the rupture dynamics, fault interactions, and the associated ground motions up to 2.5 Hz. All models account for regional seismotectonics, topo‐bathymetry, 3‐D subsurface velocity, viscoelastic attenuation, and off‐fault plasticity, and we explore the effect of fault roughness. The rupture scenarios obey earthquake scaling relations and predict magnitudes comparable to those of historical events. We show how fault system geometry and segmentation, hypocenter location, and prestress can affect the potential for rupture cascading, leading to varying slip distributions across different portions of the fault system. Our earthquake scenarios yield spatially heterogeneous near‐field ground motions modulated by geometric complexities, topography, and rupture directivity, particularly in the near‐field. The average ground motion attenuation characteristics of dynamic rupture scenarios of comparable magnitudes and mean stress drop are independent of variations in source complexity, magnitude‐consistent and in good agreement with the latest regional empirical ground motion models. However, physics‐based ground motion variability changes considerably with fault‐distance and increases for unilateral compared to bilateral ruptures. Systematic variations in physics‐based near‐fault ground motions provide important insights into the mechanics and potential earthquake hazard of large strike‐slip fault systems, such as the HFFZ. Plain Language Summary: The Húsavík‐Flatey Fault Zone (HFFZ) is the largest strike‐slip fault in Iceland, located in the Tjörnes Fracture Zone in Northern Iceland where the largest earthquakes in Iceland have occurred. At present the seismogenic potential of HFFZ suggests that an earthquake of magnitude ∼7 is possible, which poses a high earthquake hazard in the region. In this study, we generate a set of plausible earthquake rupture scenarios on the HFFZ that account for multi‐physics, regional geology and topo‐bathymetry. We simulate the corresponding seismic ground motions by exploring various assumptions, for example, in terms of slipping fault geometry and hypocenter locations. Our simulated scenarios have comparable magnitudes with historic events. The physics‐based ground motion scaling conforms to new empirical ground motion models, but shows varying ground motion variability with distance. Our study provides an overview of multiple rupture scenarios on the HFFZ and suggests that an ensemble of physics‐based dynamic rupture scenarios can complement classical seismic hazard assessment methods to better characterize the hazard in tectonically and seismically complex regions, especially in data‐scarce regions. Key Points: Observational constrained dynamic rupture scenarios of the Húsavík‐Flatey Fault Zone match expected regional earthquake scaling and magnitudesSegmented fault geometry, hypocenter location, fault prestress and roughness affect rupture dynamics and ground motionsOur physics‐based scenarios show magnitude‐consistent average attenuation relationships and match empirical ground motion models [ABSTRACT FROM AUTHOR]

We study the effects of pore fluid pressure (Pf) on the pre‐earthquake, near‐fault stress state, and 3‐D earthquake rupture dynamics through six scenarios utilizing a structural model based on the 2004 Mw 9.1 Sumatra‐Andaman earthquake. As pre‐earthquake Pf magnitude increases, effective normal stress and fault shear strength decrease. As a result, magnitude, slip, peak slip rate, stress drop, and rupture velocity of the scenario earthquakes decrease. Comparison of results with observations of the 2004 earthquake support that pre‐earthquake Pf averages near 97% of lithostatic pressure, leading to pre‐earthquake average shear and effective normal tractions of 4–5 and 22 MPa. The megathrust in these scenarios is weak, in terms of low mean shear traction at static failure and low dynamic friction coefficient during rupture. Apparent co‐seismic principal stress rotations and absolute post‐seismic stresses in these scenarios are consistent with the variety of observed aftershock focal mechanisms. In all scenarios, the mean apparent stress rotations are larger above than below the megathrust. Scenarios with larger Pf magnitudes exhibit lower mean apparent principal stress rotations. We further evaluate pre‐earthquake Pf depth distribution. If Pf follows a sublithostatic gradient, pre‐earthquake effective normal stress increases with depth. If Pf follows the lithostatic gradient exactly, then this normal stress is constant, shifting peak slip and peak slip rate updip. This renders constraints on near‐trench strength and constitutive behavior crucial for mitigating hazard. These scenarios provide opportunity for future calibration with site‐specific measurements to constrain dynamically plausible megathrust strength and Pf gradients. Plain Language Summary: Large volumes of fluid can lead to high‐pressures that weaken rocks in fault zones and influence earthquake rupture. While fluids are critical to understanding behavior at subduction zones, where the largest earthquakes in the world occur and where tsunami generation increases hazard, measuring fluid and fluid pressure directly across an entire megathrust currently is not possible. Here, we use supercomputers to model the devastating 2004 Mw 9.1 Sumatra‐Andaman earthquake in 3‐D in order to isolate the role of fluid pressure on earthquake behavior. By first building a reliable base model and then varying fluid pressure to generate six earthquake scenarios, we find that fluid pressure is likely very high, and also that the way that fluid pressure varies with depth can greatly influence the earthquake and associated hazard. Fluid pressure controls location of the largest and fastest fault slip along the megathrust, and the possibility for a devastating tsunami. Key Points: Three‐dimensional dynamic rupture modeling of megathrust earthquakes under varying pore fluid conditions reveal very high pre‐earthquake fluid pressureWhen pore fluid pressure increases with the lithostatic gradient, peak slip and peak slip rate occur at shallower depths, controlling hazardApparent co‐seismic principal stress rotations and heterogeneous absolute post‐seismic stress states reflect aftershock focal mechanisms [ABSTRACT FROM AUTHOR]

The kinematic rupture process of the 2011 M 9.0 Tohoku earthquake is inverted with an elliptical-patches method, using a genetic algorithm, for the purpose of rapid and robust estimation of the source parameters of a mega-earthquake. We use the ground-displacement field provided by a continuous GPS network and the ground-velocity field recorded by acceleration networks. In addition to the typical inversion procedure in which a data duration long enough to cover the whole rupture process is used, inversions based on shorter signals, giving an incomplete view over the ground shaking sequence, are also carried out. How fast can a robust estimation of the source parameters be obtained? Using the elliptical approximation, we find that robust solutions of M ~ 9.0-earthquakes are rather quickly obtained regardless of the frequency band and the elliptical patch description. It is also confirmed that, because of the absence of off-shore recording stations on the east side of the fault, some uncertainties in the rupture process cannot be completely removed. In fact, at the very low frequencies considered, the western part of the fault (deeper portion) contributes more significantly to the recorded signals than does the other end close to the trench. This problem also prevents refinement of the description of the rupture process, in particular when using more than one ellipse. [ABSTRACT FROM AUTHOR]

We perform numerical simulations of dynamic rupture processes along the North Anatolian fault in the Sea of Marmara, which poses a high risk to the nearby city of Istanbul. Several fault geometry models, nucleation points, and initial stress states are tested. The likelihood of each earthquake scenario is evaluated, and a probabilistic assessment of the ground-motion estimation is proposed. The simulation results suggest that the fault geometrical configuration is not favorable for producing an earthquake of magnitude 6-7, as no scenario is found. On the contrary, the probability of occurrence of an earthquake of magnitude greater than 7 is high. Most of these large events are characterized by epicenters located in the central or eastern parts of the Sea of Marmara. However, the possibility of a western-initiated rupture propagating eastward, the worst scenario for the Istanbul region, cannot be ruled out. Many simulations led to supershear ruptures, as observed for the nearby 1999 İzmit earthquake, and this significantly influences ground-motion prediction in the region. [ABSTRACT FROM AUTHOR]

The assessment of historical elements at risk from earthquake loading presents a number of differences from the seismic evaluation of modern structures, for design or retrofitting purposes, which is covered by existing building codes, and for the development of fragility curves, procedures for which have been extensively developed in the past decade. This article briefly discusses: the hazard framework for historical assets, including a consideration of the appropriate return period to be used for such elements at risk; the intensity measures that could be used to describe earthquake shaking for the analysis of historical assets; and available approaches for their assessment. We then discuss various unique aspects of historical assets that mean the characterisation of earthquake loading must be different from that for modern structures. For example, historical buildings are often composed of heterogeneous materials (e.g., old masonry) and they are sometimes located where strong local site effects occur due to: steep topography (e.g., hilltops), basin effects or foundations built on the remains of previous structures. Standard seismic hazard assessment undertaken for modern structures and the majority of sites is generally not appropriate. Within the PERPETUATE project performance-based assessments, using nonlinear static and dynamic analyses for the evaluation of structural response of historical assets, were undertaken. The steps outlined in this article are important for input to these assessments. [ABSTRACT FROM AUTHOR]

Finite difference simulations of seismic wave propagation are performed in the Niigata area, Japan, for the 2007 Mw 6.6 Niigata-ken Chuetsu-Oki earthquake at low frequencies. We test three 3D structural models built independently in various studies. First aftershock simulations are carried out. The model based on 3D tomography yields correct body waves in the near field, but later phases are imperfectly reproduced due to the lack of shallow sediment layers; other models based on various 1D/2D profiles and geological interpretation provide good site responses but generate seismic phases that may be shifted from those actually observed. Next, for the mainshock simulations, we adopt two different finite source models that differ in the near-field ground motion, especially above the fault plane (but under the sea) and then along the coastline. Each model is found to be calibrated differently for the given stations. For engineering purposes, the variations observed in simulated ground motion are significant, but for seismological purposes, additional parameter calibrations would be possible for such a complex 3D case. [ABSTRACT FROM AUTHOR]

On 14 November 2016, the Northern part of New Zealand's South Island was struck by the Mw7.8 Kaikōura earthquake, an event of unprecedented geometric complexity rupturing at least 21 segments of the contractional North Canterbury and of the Marlborough fault systems. Geological, geodetic, tsunami and seismic data reveal puzzling features as well as observational difficulties of the event leading to competing views on its key features, such as the role played by the Hikurangi subduction interface, the exact rupture sequence, and the higher than expected local tsunami. We present a dynamic rupture model of the 2016 Mw 7.8 Kaikōura earthquake to unravel the event's riddles in a physics-based manner and provide insights on the mechanical viability of competing hypotheses proposed to explain them. The event is modeled using the open-source software SeisSol (www.seissol.org), based on a arbitrary high-order accurate DERivative Discontinuous Galerkin method (ADER-DG). We verify our model with strong ground-motions, high rate GPS, long-period teleseismic and tsunami data. Our model reproduces key characteristics of the event and constraints puzzling features inferred from high-quality observations including a large gap separating surface rupture traces, the possibility of significant slip on the subduction interface, the non-rupture of the Hope fault, and slow apparent rupture speed. We show that a rupture cascade sequentially breaking the Papatea and Kekerengu faults is dynamically consistent with regional stress estimates and a crustal fault network geometry inferred from seismic and geodetic data. A coseismically triggered tsunami caused by the rare occurrence of an earthquake starting on-land and crossing to two faults off-shore matches local tide gauge data.We find, that such complex rupture cascade links the crustal fault system when operating at low apparent friction thanks to the combined effects of overpressurized fluids, low dynamic friction and stress concentrations induced by deep fault creep. Understanding the physical conditions that allow rupture cascades on complex fault systems advances our ability to quantify earthquake hazard, especially to evaluate the possibility of extreme events on real fault networks. [ABSTRACT FROM AUTHOR]

The 2004 Mw 9.1-9.3 Great Sumatra-Andaman Earthquake is one of the strongest and most devastating earthquakes in recent history. It generated a powerful tsunami, causing more than 220,000 fatalities. Despite its huge spatial extent, the analysis of the earthquake is impeded by a lack of near-source observations. Static ground-deformation data, polluted by significant after-slip in the near-source region, and teleseismic data do not fully constrain the source, leading to significant differences in its characterization. Specifically, the tsunamigenic aspects of the earthquake, such as the large but mostly horizontal seafloor displacements and potential splay fault activation, remain puzzling.In this study, we investigate the earthquake using high-resolution 3D dynamic rupture simulations. We use the open-source software SeisSol (www.seissol.org) which is based on an arbitrary high-order accurate DERivative Discontinuous Galerkin method (ADER-DG). We account for complex megathrust-splay fault geometries, high resolution topography and bathymetry, 3D subsurface structure and off-fault plasticity. We resolve the full frictional sliding process as well as the seismic wave field in the to-date longest (500 s) and largest (1500 km) dynamic rupture earthquake scenario.We discuss macroscopic earthquake source characteristics inferred from a smoothly initialized model, in which we prescribe regional, smoothly varying fault pre-stresses constrained by earthquake focal mechanisms, interacting with frictional fault conditions changing only depth-dependently. The interplay of complex fault geometry and simple pre-stress state yields good agreement of ground-deformations in the near field and very long-period teleseismic data. We are specifically interested in the effects of off-fault plasticity: overall reducing rupture speed but increasing or decreasing fault slip depending on regional stress orientation in conjunction with the fault geometry. We then refine the regional stress state based on static inversion and mechanical viability arguments to fully capture dynamic features such as lower slip release in the Southern megathrust and slow rupture velocity at around 8° latitude. Our models are verified by generating synthetic geodetic, teleseismic and tsunami records, employing off-line coupling of SeisSol to established global seismic wave propagation and tsunami simulation tools. [ABSTRACT FROM AUTHOR]

The destructive 2023 moment magnitude (Mw) 7.8-7.7 earthquake doublet ruptured multiple segments of the East Anatolian Fault system in Turkey. We integrated multiscale seismic and space-geodetic observations with multifault kinematic inversions and dynamic rupture modeling to unravel the eventsÕ complex rupture history and stress-mediated fault interactions. Our analysis reveals three subshear slip episodes during the initial Mw 7.8 earthquake with a delayed rupture initiation to the southwest. The Mw 7.7 event occurred 9 hours later with a larger slip and supershear rupture on its western branch. Mechanically consistent dynamic models accounting for fault interactions can explain the unexpected rupture paths and require a heterogeneous background stress. Our results highlight the importance of combining near- and far-field observations with data-driven and physics-based models for seismic hazard assessment. [ABSTRACT FROM AUTHOR]

• Families of dynamic models can guarantee the mechanical viability of kinematic models. • Geological constraints can ensure the compatibility of the assumed friction values. • The developed approach permits to validate the plausibility of kinematic models. • Dynamic scenarios match seismic and geodetic observations and geological constraints. The 2016 Central Italy earthquake sequence is characterized by remarkable rupture complexity, including highly heterogeneous slip across multiple faults in an extensional tectonic regime. The dense coverage and high quality of geodetic and seismic data allow us to image intriguing details of the rupture kinematics of the largest earthquake of the sequence, the M w 6.5 October 30th, 2016 Norcia earthquake, such as an energetically weak nucleation phase. Several kinematic models suggest multiple fault planes rupturing simultaneously, however, the mechanical viability of such models is not guaranteed. Using 3D dynamic rupture and seismic wave propagation simulations accounting for two fault planes, we constrain "families" of spontaneous dynamic models informed by a high-resolution kinematic rupture model of the earthquake. These families differ in their parameterization of initial heterogeneous shear stress and strength in the framework of linear slip weakening friction. First, we dynamically validate the kinematically inferred two-fault geometry and rake inferences with models based on only depth-dependent stress and constant friction coefficients. Then, more complex models with spatially heterogeneous dynamic parameters allow us to retrieve slip distributions similar to the target kinematic model and yield good agreement with seismic and geodetic observations. We discuss the consistency of the assumed constant or heterogeneous static and dynamic friction coefficients with mechanical properties of rocks at 3-10 km depth characterizing the Italian Central Apennines and their local geological and lithological implications. We suggest that suites of well-fitting dynamic rupture models belonging to the same family generally exist and can be derived by exploiting the trade-offs between dynamic parameters. Our approach will be applicable to validate the viability of kinematic models and classify spontaneous dynamic rupture scenarios that match seismic and geodetic observations as well as geological constraints. [ABSTRACT FROM AUTHOR]

We present a coupled modeling approach of large-scale physics-based dynamic earthquake rupture simulations to tsunami propagation and inundation models. Two simple test cases are designed illustrating earthquake-tsunami interaction and establishing baselines for realistic coupled scenarios. The 3D earthquake models incorporate a planar fault, extending from the seafloor to 35 km depth, dipping 16 degrees, and surrounded by a homogeneous crust. They are run with SeisSol (www.seissol.org), which can incorporate many aspects of realistic source physics, such as geometrically complex fault systems, various modern friction laws and off-fault plasticity, all in the framework of efficient HPC computation. The modeled time-dependent seafloor displacements are used as the source in the tsunami model with the help of ASAGI, an open-source library with a simple interface to access Cartesian material and geographic datasets in massively parallel simulations. An accurate and efficient representation of the evolution of the tsunami and the following coastal inundation are achieved with an adaptive mesh discretizing the shallow water equations with a Runge-Kutta discontinuous Galerkin scheme. Across-model complexity is explored using earthquake sources both with and without elevated near-trench cohesion. We specifically compare tsunami models using static (final) versus dynamic (time-dependent) seafloor displacements as sources. In order to better constrain the initial conditions governing earthquake models, we further present the ASCETE framework, which couples a subduction zone seismic cycle model to the earthquake and tsunami models. The seismic cycle model is a 2D seismo-thermo-mechanical simulation of long term deformation. Slip instabilities that approximate earthquakes arise spontaneously within the subduction zone channel. Within this framework, we attain physically consistent initial conditions for a megathrust earthquake, capture the full dynamics of the rupture, and determine the resulting seafloor displacements to source the tsunami. This work is part of the project "Advanced Simulation of Coupled Earthquake and Tsunami Events" (ASCETE), funded by the Volkswagen Foundation. [ABSTRACT FROM AUTHOR]

The highest earthquake hazard in Egypt and Saudi Arabia is close to Gulf of Aqaba and Strait of Tiran (at the gulf's southern end), an area we refer to as GAST. The hazard is due to the left-lateral Dead Sea transform fault system, which at this location is trans-tensional with three major basins within the gulf and one more immediately south of the strait. While the fault system has produced many devastating earthquakes to the north of Aqaba in the past 2000 years, less is known about historical earthquakes in the GAST area. The last major earthquake occurred in 1995 (Mw=7.3) in the central part of the gulf and it caused several fatalities and considerable damage both in Egypt and in Saudi Arabia. The 1995 earthquake only ruptured a part of fault system within the gulf, leaving other segments undisturbed that have not ruptured for several centuries. Saudi Arabia and Egypt have decided to build a bridge across Strait of Tiran, linking the two countries, and construction of an entirely new high-tech city (NEOM) has started on the Saudi side of the gulf. These major infrastructure projects have greatly increased the need for better knowledge about the earthquake hazard in the GAST area. To address this challenge, we have started an international and interdisciplinary project aimed at locating the active faults in the gulf and constraining better its overall tectonics, as well as obtaining new information about how frequent and how large major earthquakes in the area likely are. The project title is "Interdisciplinary earthquake hazard research in Gulf of Aqaba and Strait of Tiran (GAST)". During a research cruise in May-June 2018 we mapped the bathymetry of large parts of the gulf with high-resolution multibeam sounder and collected 23 sediment cores in search for evidence of past major earthquakes. The multibeam data show well the locations of the active fault strands leading to a new fault map of the GAST area. In addition, to learn more about the structure and activity of normal faults bounding the basins in the gulf, we carried out a seismic survey along a 7 km long profile, crossing one of the onshore faults, as well as collected and dated samples from uplifted coral terraces along the gulf's coastline. Furthermore, we installed a new GPS network in the area and the results of the first remeasurements show well the relative motion across the gulf, which helps to constrain better the moment accumulation rate in the area. The collected sediment cores show clear evidence of the 1995 earthquake and two older earthquakes, of which one is likely the 1588 earthquake. Finally, using earthquake scenario calculations, we are estimating expected shaking levels of possible future major earthquakes occurring on faults in the GAST area. Together the results will significantly improve knowledge of the active tectonics in the Gulf of Aqaba area and provide valuable information for future seismic hazard assessments. [ABSTRACT FROM AUTHOR]