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Numerical modeling of earthquake dynamics and derived insight for seismic hazard relies on credible, reproducible model results. The sequences of earthquakes and aseismic slip (SEAS) initiative has set out to facilitate community code comparisons, and verify and advance the next generation of physics-based earthquake models that reproduce all phases of the seismic cycle. With the goal of advancing SEAS models to robustly incorporate physical and geometrical complexities, here we present code comparison results from two new benchmark problems: BP1-FD considers full elastodynamic effects, and BP3-QD considers dipping fault geometries. Seven and eight modeling groups participated in BP1-FD and BP3-QD, respectively, allowing us to explore these physical ingredients across multiple codes and better understand associated numerical considerations. With new comparison metrics, we find that numerical resolution and computational domain size are critical parameters to obtain matching results. Codes for BP1-FD implement different criteria for switching between quasi-static and dynamic solvers, which require tuning to obtain matching results. In BP3-QD, proper remote boundary conditions consistent with specified rigid body translation are required to obtain matching surface displacements. With these numerical and mathematical issues resolved, we obtain excellent quantitative agreements among codes in earthquake interevent times, event moments, and coseismic slip, with reasonable agreements made in peak slip rates and rupture arrival time. We find that including full inertial effects generates events with larger slip rates and rupture speeds compared to the quasi-dynamic counterpart. For BP3-QD, both dip angle and sense of motion (thrust versus normal faulting) alter ground motion on the hanging and foot walls, and influence event patterns, with some sequences exhibiting similar-size characteristic earthquakes, and others exhibiting different-size events. These findings underscore the importance of considering full elastodynamics and nonvertical dip angles in SEAS models, as both influence short- and long-term earthquake behavior and are relevant to seismic hazard.

This zip file contains the SeisSol input files necessary to create a mesh and to perform the dynamic rupture simulations described in "Fault-size dependent fracture energy explains multi-scale seismicity and cascading earthquakes".The detailed description of each file and SeisSol version used is described in README, and parameter choice is explained in each ".yaml" and parameter file.

This zip file contains the SeisSol input files necessary to create a mesh and to perform the dynamic rupture simulations described in "Rupture Dynamics of Cascading Earthquakes in a Multiscale Fracture Network".The detailed description of each file and SeisSol version used is described in README, and parameter choice is explained in each ".yaml" and parameter file.

Transients of aseismic fault slip, slow slip events (SSEs), have been observed in spatial and temporalproximity to the initiation of megathrust earthquakes. However, the underlying physics potentially connecting a preceding SSE to earthquake rupture remains to be determined. Here, we link 3Dobservation-driven slow-slip cycle models with dynamic rupture simulations of the 2014 Mw7.3 Guerrero, Mexico earthquake across the geometrically complex flat-slab Cocos plate. Our physics-based models reproduce key regional geodetic and teleseismic observations on timescales ranging from decades toseconds. We find that accelerating SSE fronts transiently increase shear stress at the down-dip end of the seismogenic portion of the megathrust. The stresses cast by the 2014 Mw 7.6 SSE are significantlylarger than those during the three previous episodic SSEs, and can dynamically initiate earthquakerupture. We show that in addition to the transient stresses caused by SSEs, megathrust asperitiesexplain the observed complexities in the coseismic energy release and static surface displacements. Weconclude that it is crucial to jointly analyze the long- and short-term interactions of SSEs and megathrustearthquakes across several (a)seismic cycles. Our study has important implications for identifyingearthquake precursors and understanding megathrust faulting processes.

A recently developed continuum formulation of rate and state friction (Pranger et al., 2022) treats fault friction as an internal flow process in a granular medium, instead of its conventional treatment as a sliding process on a surface between juxtaposed rocks. The spurious mesh dependency that is typically associated with strain softening rheologies is avoided by including a diffusion process with an associated diffusion length scale.We show that this granular rate and state friction law can be understood as a flow involving the breakage component of the damage-breakage rheology (DBR) of Lyakhovsky and Ben Zion (2014a,b). Modeling the episodic transitions from local damage accumulation in the solid to the fluid-like granular flow phase during larger collective failure events, the DBR is both significantly broader in scope and better grounded in the thermodynamic theory of irreversible processes than the phenomenological rate and state friction law.A promising next step is to consider the damage and breakage components simultaneously in coupled continuum models of fault and rupture co-evolution. Doing so at sufficient resolution requires highly performant algorithms and a specialized numerical treatment of the coupled non-linear partial differential equations, including a robust time integration scheme with adaptive step size control and a flexible implicit-explicit split. We aim to discuss our numerical methods and computing paradigms supported by proof-of-concept modeling results of interacting damage and breakage pulses in 2D.References:Pranger et al. (2022), Rate and state friction as a spatially regularized transient viscous flow law. Journal of Geophysical Research: Solid Earth, 127, e2021JB023511.Lyakhovsky and Ben-Zion (2014a), Damage–breakage rheology model and solid-granular transition near brittle instability. Journal of the Mechanics and Physics of Solids, 64, 184-197.Lyakhovsky and Ben-Zion (2014b), A Continuum Damage–Breakage Faulting Model and Solid-Granular Transitions. Pure and Applied Geophysics, 171, 3099–3123

The second phase (2023-2026) of the Center of Excellence for Exascale in Solid Earth (ChEESE-2P), funded by HORIZON-EUROHPC-JU-2021-COE-01 under the Grant Agreement No 101093038, will prepare 11 European flagship codes from different geoscience domains (computational seismology, magnetohydrodynamics, physical volcanology, tsunamis, geodynamics, and glacier hazards). Codes will be optimised in terms of performance on different types of accelerators, scalability, containerisation, and continuous deployment and portability across tier-0/tier-1 European systems as well as on novel hardware architectures emerging from the EuroHPC Pilots (EuPEX/OpenSequana and EuPilot/RISC-V) by co-designing with mini-apps. Flagship codes and workflows will be combined to farm a new generation of 9 Pilot Demonstrators (PDs) and 15 related Simulation Cases (SCs) representing capability and capacity computational challenges selected based on their scientific importance, social relevance, or urgency. The SCs will produce relevant EOSC-enabled datasets and enable services on aspects of geohazards like urgent computing, early warning forecast, hazard assessment, or fostering an emergency access mode in EuroHPC systems for geohazardous events including access policy recommendations. Finally, ChEESE-2P will liaise, align, and synergise with other domain-specific European projects on digital twins and longer-term mission-like initiatives like Destination Earth.

The instantaneous weakening of rocks during the passage of seismic waves has first been observed in laboratory experiments. The change of elastic rock moduli during and after the dynamic perturbations typically includes three phases – a gradual drop of moduli, a dynamically steady state and the recovery over a time scale that is larger than that of the perturbations. Such changes have been referred to as slow dynamics (Johnson and Sutin, 2005). With the development of the long-term continuous monitoring of the velocity field inside the Earth using methods such as ambient noise interferometry, coseismic rock weakening and post-seismic recovery of rock strength have also been recorded in the field over the past two decades. The question that we want to answer is: how relevant is the non-classical nonlinearity observed in the lab to the coseismic velocity drop in the field? To this end, we aim to adapt an analytical model that explains the lab observations and apply it to field observations using numerical simulations. Our first step is to identify the appropriate nonlinear model(s). Most of the proposed physical models that explain the phenomenon contain many parameters and are hard to constrain. Moreover, most of the existing physical models are restricted to 1D analysis and are difficult to generalize to 2D or 3D modeling. We apply two models within the framework of the continuum damage mechanics: (i) the internal variable model (Berjamin et al., 2017) and (ii) the continuum damage model that accounts for parallel micro-cracks oriented perpendicular to the maximum tension or compression (Lyakhovsky et al., 1997). Both models can generalize to 2D and 3D. We formulate both models as nonlinear hyperbolic partial differential equations (PDEs) and solve them with the arbitrary high-order discontinuous Galerkin method using ExaHyPE (Reinarz et al., 2020) in 2D and 3D. We show that both models successfully reproduce the three phases during and after dynamic perturbations observed in the laboratory. We find that the continuum damage model can explain the amplitude- and frequency-dependent damage with a good match against the lab measurements. We also compare the simulation results using both models quantitatively with the observations in a 2D copropagating acousto-elastic testing (Feng et al., 2018). Our sensitivity analysis of the model parameters using the Markov chain Monte Carlo method quantitatively estimates the uncertainties and correlations among the parameters of both models. We believe our work paves the way towards a model of nonlinear rock deformation with slow dynamics that can be used in large scale 2D and 3D seismic wave propagation simulations for direct analysis of field observations, such as the Tohoku earthquake, 2011 (Brenguier et al., 2014).

Destination Earth initiative pursues the implementation of a digital model of the Earth. With the aim to help understand and simulate the evolution and behavior of the Earth system components, to aid in better forecasting the impacts on human system processes, ecosystem processes and their interaction. The current state of the art technologies in numerical computations (HPC), data infrastructures (involving data storage, data access, data analysis), enable the possibility of developing numerical clones mimicking Earth’s geophysical extreme phenomena.A Digital Twin for GEOphysical extremes (DT-GEO),is a new EU project funded under the Horizon Europe programme (2022-2025), with the objective of developing a prototype for a digital twin on geophysical extremes including earthquakes, volcanoes, tsunamis, and anthropogenic-induced extreme events. It will enable analyses, forecasts, and responses to “what if” scenarios for natural hazards from their genesis phases and across their temporal and spatial scales. The project consortium brings together world-class computational and data Research Infrastructures (RIs), operational monitoring networks, and leading-edge research and academia partnerships in various fields of geophysics. It mergesthe latest outcomes from other European projects and, Centers of Excellence. DT-GEO will deploy and test 12 Digital Twin Components (DTCs). These will be self-contained entities embedding flagship simulation codes, Artificial Intelligence layers, large volumes of (real-time) data streams from and into data-lakes, data assimilation methodologies, and overarching workflows for deployment and execution of single or coupled DTCs in centralized HPC and virtual cloud computing Ris. (DT-GEO: A Digital Twin for GEOphysical extremes, project ID 101058129)

The destruction unfolding after the February 6, 2023 Turkey-Syria Earthquake sequence is devastating. First observations reveal complex earthquake dynamics challenging data-driven efforts. We present rapid, data-informed and physics-based 3D dynamic rupture simulations of the puzzling Mw7.8 Kahramanmaras earthquake providing a first-order mechanical explanation of this earthquake’s complexity and its implications for the Mw7.5 doublet event.By incorporating detailed fault geometries constrained by satellite geodetic observations into 3D dynamic rupture simulations, we show how dynamic interactions between fault geometric complexity and the heterogeneous regional stress field generated the unique and unexpected rupture behaviors observed, including localized supershear, backwards rupture branching, and locally strong shaking.Our supercomputing empowered simulations that tightly link earthquake physics with interdisciplinary observations can provide a direct understanding of the fault system mechanics, reconcile competing interpretations and serve as a constraint to understand the short- and long-term Eastern Anatolian Fault system interaction.

Seismic array processing is routinely used to infer detailed earthquake properties of intermediate and large events, however, the source properties of microseismicity often remain elusive. In this study, we use high signal-to-noise ratio seismograms of 204 earthquakes induced by the 6 km deep 2018 Espoo/Helsinki geothermal stimulation to evaluate the capabilities of beamforming and back-projection array methods. We show that mini array beamforming is sensitive to medium heterogeneity and requires calibration to mitigate systematic slowness biases.A combined and wave back-projection approach significantly improves depth resolution, reducing offsets to catalogue locations from km to m. Supported by numerical experiments, we demonstrate that back-projection swimming patterns can constrain focal mechanisms. Our results imply that back-projection of data collected over a wide azimuthal range can be used to monitor and characterize local-scale microseismicity, whereas beamforming calibration requires independently obtained reference observations.

The Husavik-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 Husavik-Flatey Fault Zone (HFFZ) is the largest strike-slip fault in Iceland, located in the Tjornes 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 similar to 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.

The overwhelming observational difficulties and the complexity of earthquake physics have rendered seismic hazard assessment largely empirical. Despite increasingly high-quality geodetic, seismic, and field observations, data-driven earthquake imaging yields stark differences and physics-based models explaining all observed dynamic complexities are elusive. Here we present data-assimilated 3D dynamic rupture models which untwine California's biggest earthquakes in more than 20 years: the moment magnitude (Mw) 6.4 Searles Valley and Mw7.1 Ridgecrest, California, sequence breaking multiple segments of the same fault system. Our models use supercomputing to find the link between the two large earthquakes. We unify the uniquely high-quality strong-motion and teleseismic, field mapping, high-rate GNSS, and space geodetic foreshock and mainshock datasets with earthquake physics. We find that the regional structure, the ambient long- and short-term stress, as well as the dynamic and static fault system interactions, are conjointly crucial to understand the dynamics and delays of the sequence. Dynamic rupture of a statically strong yet dynamically weak fault system is driven by overpressurized fluids and low dynamic friction in our models. The observed earthquake complexity results from static and dynamic stress changes acting across a non-vertical quasi-orthogonal conjugate fault structure. We demonstrate that joint physics-based and data-driven illumination of the mechanics of complex fault systems and earthquake sequences is possible when reconciling dense earthquake recordings, 3D regional structure and stress models. We foresee that physics-based interpretation of big observational data-sets characterizing complex nonlinear systems will have a transformative impact on future geohazard mitigation.

Special issue EPOS a Research Infrastructure in solid Earth: open science and innovation .-- 21 pages, 8 figures, Tsunamis constitute a significant hazard for European coastal populations, and the impact of tsunami events worldwide can extend well beyond the coastal regions directly affected. Understanding the complex mechanisms of tsunami generation, propagation, and inundation, as well as managing the tsunami risk, requires multidisciplinary research and infrastructures that cross national boundaries. Recent decades have seen both great advances in tsunami science and consolidation of the European tsunami research community. A recurring theme has been the need for a sustainable platform for coordinated tsunami community activities and a hub for tsunami services. Following about three years of preparation, in July 2021, the European tsunami community attained the status of Candidate Thematic Core Service (cTCS) within the European Plate Observing System (EPOS) Research Infrastructure. Within a transition period of three years, the Tsunami candidate TCS is anticipated to develop into a fully operational EPOS TCS. We here outline the path taken to reach this point, and the envisaged form of the future EPOS TCS Tsunami. Our cTCS is planned to be organised within four thematic pillars: (1) Support to Tsunami Service Providers, (2) Tsunami Data, (3) Numerical Models, and (4) Hazard and Risk Products. We outline how identified needs in tsunami science and tsunami risk mitigation will be addressed within this structure and how participation within EPOS will become an integration point for community development, With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

High-resolution observations show that large earthquakes commonly involve slip on multiple faults along with localized and distributed inelastic off-fault damage. Despite a lack of modern large earthquakes on shallowly dipping detachments, Holocene Mw>7 detachment ruptures are preserved in the paleoseismic record and inferred from historical accounts of such earthquakes and resulting tsunamis. Even in well-recorded megathrust earthquakes, the effects of non-linear off-fault plasticity and dynamically reactivated splay faults on shallow deformation and surface displacements, and thus hazard, remain elusive. Here, we develop geologically, geodetically and geophysically constrained 3D dynamic rupture models of the active Mai’iu fault in Papua New Guinea that highlight how multiple dynamic shallow deformation mechanisms compete in large detachment earthquakes. We show that splay faults in the detachment’s hanging wall are likely to rupture coseismically, with more slip expected on splays that dip at shallow angles synthetic to the detachment. Inelastic off-fault yielding in the hanging wall localizes into subplanar shear bands indicative of newly initiated splay faulting, most prominently above detachments with thick sedimentary basins in their hanging walls. Dynamic splay faulting and sediment failure limit shallow detachment rupture, modulating coseismic subsidence patterns, near-shore slip velocities, and the seismic and tsunami hazards posed by detachment earthquakes.

Back azimuth (BAz) information can be determined from combined measurements of rotations and translations at a single site. Such six degree-of-freedom (6-DoF) measurements are reasonably stable in delivering similar information compared to a small-scale array of three-component seismometers. Here we investigate whether a 6-DoF approach is applicable to tracking seismic sources. While common approaches determining the timing and location of energy sources generating seismic waves rely on the information of P-waves, here we use S-waves. We track back azimuths of directly arriving SH-waves in the two-dimensional case, P-converted SV-waves, direct SV- and direct SH-waves in the three-dimensional case. For data analysis, we compare a cross-correlation approach using a grid-search optimization algorithm with a polarization analysis method. We successfully recover the rupture path and rupture velocity with only one station, under the assumption of an approximately known fault location. Using more than one station, rupture imaging in space and time is possible without a priori assumptions. We discuss the effects of rupture directivity, supershear rupture velocity, source-receiver geometry, wavefield interference, and noise. We verify our approach with the analysis of moving traffic noise sources using 6-DoF observations. The collocated classic seismometer and newly built ring laser gyroscope ROMY near Munich, Germany, allow us to record high-fidelity, broadband 6-DoF (particle velocity and rotational rate) ground motions. We successfully track vehicles and estimate their speed while traveling along a nearby highway using the estimated BAz as a function of time of a single station observation.

The Hellenic Arc is an active seismogenic zone in the Mediterranean Sea that hosted at least two historical M≥8 earthquakes, which both caused destructive tsunamis. The low-angle geometry of its subduction interface could promote shallow slip amplification, enhancing seafloor displacement. Long-term seismic-probabilistic tsunami hazard assessment (S-PTHA, e.g., Scala et al., 2020) and early warning systems typically rely on kinematic models and Okada's analytical solution to compute static seafloor displacements. The static displacement is then used to source tsunami models. However, the complex interaction of earthquake dynamics and tsunami-genesis may not be fully captured.We recently demonstrated mechanically consistent dynamic rupture models in generic megathrust settings informed from long-term geodynamic modeling that can provide building blocks toward integrating physics-based dynamic rupture modeling in Probabilistic Tsunami Hazard Analysis (Wirp et al., 21). We here present a range of 3D multi-physics, high-resolution dynamic rupture subduction earthquake scenarios accounting for the complex slab geometry of the Hellenic Arc. We vary hypocenter locations, which leads to a wide range of rupture speeds, extent of shallow fault slip, and moment magnitudes. Our dynamic rupture models include highly resolved bathymetry and topography data and detailed knowledge of the tectonic structure of the Hellenic Arc (seismic velocity structure, stresses, and strengths). We use the slab geometry from the European Database of Seismogenic Faults (EDSF, Basili et al., 2013) to create a 3D dynamic rupture scenario that covers great parts of the Mediterranean Sea. The initial conditions in our models are constrained on the subduction zone scale (Ulrich et al., 2021) and specified for the Hellenic Arc region.Only part of the Hellenic Arc is fully seismically coupled (e.g., Laigle et al., 2004) and most of the convergence is assumed to occur as aseismic creep. We follow Ramos et al. (2021) and apply different friction parameters accounting for high or low coupling of the plate interface.Our modeling suggests that margin-wide rupture would yield an Mw 9.3 earthquake. More reasonable smaller magnitude earthquakes are obtained by increasing the along-arc complexity of the reference model. Different hypocenter locations result in remarkable differences in shallow fault slip penetrating into velocity-strengthening regions, which translate into strong variations of the final seafloor displacement across scenarios. In additional models with partially consolidated and totally unconsolidated sediments (Ulrich et al., 2021) we show that off-fault plastic yielding, which limits shallow fault slip, may drastically increase the seafloor uplift. Finally, we explore a novel 3D fully coupled earthquake-tsunami modeling approach (Lotto and Dunham, 2018; Krenz et al., 2021) by adding a water layer to the modeling domain. This enables simulating earthquake dynamics, acoustic waves, and the resulting tsunami simultaneously. The fully coupled model will capture the dynamics of the entire tsunami-genesis in a single simulation, overcoming typical approximations for standard earthquake-tsunami coupling workflows. We envision that mechanically consistent dynamic rupture models can provide building blocks toward combined, self-consistent, and physics-based Seismic and Tsunami Hazard Analysis.

The 15 November 2017 Mw 5.5 Pohang, South Korea, earthquake has been linked to hydraulic stimulation and fluid injections, making it the largest induced seismic event associated with an enhanced geothermal system. To understand its source dynamics and fault interactions, we conduct the first 3D high-resolution spontaneous dynamic rupture simulations of an induced earthquake. We account for topography, off-fault plastic deformation under depth-dependent bulk cohesion, rapid velocity weakening friction, and 1D subsurface structure. A guided fault reconstruction approach that clusters spatiotemporal aftershock locations (including their uncertainties) is used to identify a main and a secondary fault plane that intersect under a shallow angle of 15°. Based on simple Mohr–Coulomb failure analysis and 180 dynamic rupture experiments in which we vary local stress loading conditions, fluid pressure, and relative fault strength, we identify a preferred two-fault-plane scenario that well reproduces observations. We find that the regional far-field tectonic stress regime promotes pure strike-slip faulting, whereas local stress conditions constrained by borehole logging generate the observed thrust-faulting component. Our preferred model is characterized by overpressurized pore fluids, nonoptimally oriented but dynamically weak faults and a close-to-critical local stress state. In our model, earthquake rupture “jumps” to the secondary fault by dynamic triggering, generating a measurable non-double-couple component. Our simulations suggest that complex dynamic fault interaction may occur during fluid-injection-induced earthquakes and that local stress perturbations dominate over regional stress conditions. Therefore, our findings have important implications for seismic hazard in active georeservoir.

The importance of pore fluid pressure (Pf) for fault strength, stress state and slip behavior holds promise for explaining spatio-temporal subduction zone megathrust behavior, but the coseismic state of Pf and its distribution with depth are poorly constrained. Here, we analyze fault stress states and 3D rupture dynamics of six scenarios based on the 2004 Mw 9.1 Sumatra-Andaman earthquake. We vary Pf from hydrostatic to lithostatic under two different gradients that result in depth-dependent versus constant effective normal stress on the seismogenic part of the megathrust. As Pf magnitude increases, fault strength, moment magnitude, cumulative slip, peak slip rate, dynamic stress drop and rupture velocity decrease. When Pf follows the lithostatic gradient, depth-constant effective normal stress results, as theoretically proposed. We find that such a near-lithostatic pore fluid pressure gradient shifts peak slip and peak slip rate up-dip. We study the dynamically modeled apparent co-seismic principal stress rotations and absolute post-seismic stress state. In all earthquake dynamic rupture scenarios, the mean apparent stress rotations are larger in the accretionary wedge than below the megathrust. Scenarios with higher Pf exhibit lower mean apparent principal stress rotations in the accretionary wedge. By comparison against observations of the 2004 Sumatra-Andaman earthquake, two preferred scenarios emerge. These support the presence of very high coseismic pore fluid pressure at 97 % of the lithostatic pressure, producing average shear and effective normal traction magnitudes of 4-5 MPa and 22 MPa, respectively. The mean dynamic stress drop for both scenario earthquakes is 3 MPa and the mean rupture velocity is 2400-2600 m/s, comparable to observations of the 2004 Sumatra earthquake. The heterogeneous post-seismic stress states in these scenarios are consistent with the variety of aftershock focal mechanisms observed after the 2004 earthquake. These two preferred scenarios differ in pore fluid pressure gradient and thus in slip on the shallow megathrust. Under conditions of very high pore fluid pressure that lead to weak megathrusts in terms of the low static shear strength and low dynamic friction during rupture, near-trench strength and constitutive behavior are crucial for megathrust hazard, as peak slip and peak slip rate occur at shallower depths. This condition also is consistent with observations that the stress drops of small earthquakes in subduction zones are only weakly depth-dependent.

The ~100 km long Húsavík Flatey Fault Zone (HFFZ) in North Iceland is the largest linear transform fault zone in Iceland composed of multiple fault segments that localise both strike-slip and normal movements, agreeing with a transtensional deformation pattern (Garcia and Dhont, 2005). With maximum seismogenic potential larger than Mw 7 and located primarily offshore, the HFFZ subjects several nearby coastal communities to potentially significant tsunami hazard from strong earthquake occurrence on the HFFZ. Namely, tsunami hazard assessment of submarine strike-slip fault systems in transtensional tectonic settings worldwide has received increased attention since the unexpected and devastating local tsunami in the Palu Bay following the 2018 Mw 7.5 Sulawesi earthquake in Indonesia.Our goal is to carry out a physics-based assessment of the tsunami potential of the HFFZ using both a one-way linked dynamic earthquake rupture and shallow water equations tsunami workflow (Madden et al., 2021) as well as a fully-coupled elastic-acoustic earthquake-tsunami simulation (Krenz et al., SC 2021). We start by simulating physics-based dynamic rupture models with varying hypocenter locations with SeisSol (https://github.com/SeisSol/SeisSol), a scientific open-source software for 3D dynamic earthquake rupture simulation (www.seissol.org). SeisSol, a flagship code of the ChEESE project (https://cheese-coe.eu) and part of the project TEAR (https://www.tear-erc.eu), enables us to explore newly inferred simple and complex fault geometries that have been compiled and proposed in the ChEESE project by using unstructured tetrahedral meshes. The linked workflow uses the time-dependent seafloor displacement output from SeisSol to initialise bathymetry perturbations within sam(oa)²-flash. The dynamically adaptive, parallel software sam(oa)²-flash (https://gitlab.lrz.de/samoa/samoa) solves the hydrostatic shallow water equations (Meister, 2016). Here we consider the contribution of the horizontal ground deformation of realistic bathymetry to the vertical displacement following Tanioka and Satake (1996). Our second approach is based on the recent development of SeisSol which allows us to include a water layer in the earthquake-tsunami simulation to account for fully-coupled 3D elastic, acoustic and tsunami wave generation and propagation simultaneously.The HFFZ is exposed to a laterally homogeneous regional stress field constrained from seismo-tectonic observations, knowledge of fault fluid pressurisation, and the Mohr-Coulomb theory of frictional failure. We are able to model large Mw 6.7 to 7.3 dynamic rupture scenarios that can generate up to 2m of vertical coseismic offset. Our simulations are controlled by spontaneous fault interaction in terms of dynamic and static stress transfer and rupture jumping across the complex fault network. The models show a dynamic rake rotation of ±20° near the surface, indicating the presence of dip-slip components. Shallow fault slip of up to 8m and off-fault plastic yielding contribute to the tsunami genesis. The sea surface height anomaly (ssha), which is measured at synthetic tide gauge stations along the coastline and defined as the deviation from the mean sea level, provides an estimate about the impact of the tsunami. Our physically informed worst-case tsunami simulation causes a total ssha amplitude of ~1m. We conclude that the HFFZ has the capability to generate localised tsunamigenic earthquakes potentially posing significant hazards to the coastline communities.

Under dynamic perturbations, it has been observed that materials like sedimentary rocks show complex mechanical behaviors. They include the simultaneous dependence of the elastic moduli and attenuation on strain at the same time scale of the perturbations, as well as the conditioning and recovery of the elastic moduli that may happen at time scales that are much larger. The latter cases were recently referred to as non-classical nonlinearity. Aside from laboratory experiments, comparable observations of the non-classical nonlinearity have been made in the field over the past two decades with the development of long-term continuous monitoring of the velocity field inside the Earth using methods such as ambient noise interferometry. A variety of mathematical models that can potentially quantify the non-classical nonlinearity have already been proposed, e.g., the Damage–Breakage Rheology Model, the Internal Variable Model and the Godunov–Peshkov–Romenski model. However, implementing them in numerical schemes suitable to reproduce nonlinear effects in wave propagation on the local, regional, or global scale is challenging. This can be of interest for constraining a more realistic dynamic rheology for the Earth with the field observations. In this work, wave propagation in different non-classical nonlinear models is implemented in FEniCS using the discontinuous Galerkin (DG) method in 1D. Behaviors of the different models are systematically studied and quantitatively compared against measurements. This work lays the foundation for an extension to the simulation of 2D/3D wave propagation in the Earth on the large-scale DG simulation frameworks, e.g., SeisSol and ExaHyPE.

Earthquake fault zones are more complex, both geometrically and rheologically, than an idealized infinitely thin plane embedded in linear elastic material. Field and laboratory measurements have revealed intense fault weakening induced by flash heating and melting on natural fault (Di Toro et al., 2006; Goldsby & Tullis, 2011) and complex fault zone structure involving both tensile and shear fractures spanning a wide spectrum of length scales (e.g., Mitchell & Faulkner, 2009). Previous 2D numerical models explicitly accounting for off-fault fractures have demonstrated important feedback with rupture dynamics and ground motions (e.g., Thomas & Bhat 2018, Okubo et al., 2019). However, numerical studies of thermal-related weakening mechanisms usually avoid frictional melting due to the lack of the solid-fluid phase transition. In the work of Gabriel et al. (2021), we have presented our first-order hyperbolic and thermodynamically compatible mathematical model, namely the GPR model (Godunov & Romenski, 1972; Romenski, 1988), combined with a diffuse crack representation to incorporate finite strain nonlinear material behavior, natural complexities and multi-physics coupling within and outside of fault zones into dynamic earthquake rupture modeling. We compare our novel diffuse interface fault models of kinematic cracks, spontaneous dynamic rupture, and dynamically generated off-fault shear cracks to sharp interface reference models. Pre-damaged faults, as well as dynamically induced secondary cracks are therein described via a scalar function indicating the local level of material damage (Tavelli et al., 2020); arbitrarily complex geometries are represented via a diffuse interface approach based on a solid volume fraction function (Tavelli et al., 2019). Here we further extend the diffuse crack representation to more complicated scenarios including severe dynamic fault zone weakening as activated by flash heating, the effect of locally melting rocks, and off-fault cracks with complex topology in 3D materials, by taking advantage of adaptive Cartesian meshes (AMR) embedded in the extreme-scale hyperbolic PDE solver ExaHyPE (Reinarz et al., 2019). We intend to compare our thermally-weakened rupture in diffused fault zone with the semi-analytical thermal pressurization weakening implemented in the linear elastodynamic rupture on an infinitely-thin fault surface, using SeisSol (https://github.com/SeisSol). We will further qualitatively verify our model using the up-to-date observations in the 2020 M8.2 Chignik, Alaska, to illustrate the importance of thermal weakening on relatively deeper faults. Our approach is part of the TEAR ERC project (www.tear-erc.eu) and will potentially allow to fully model volumetric fault zone shearing during earthquake rupture, which includes spontaneous partition of fault slip into intensely localized shear deformation within weaker (possibly cohesionless/ultracataclastic) fault-core gouge and more distributed damage within fault rocks and foliated gouges.

Broadband earthquake ground motion simulations (>1 Hz) are of great interest to seismologists and the earthquake engineering community. The evolution of the earthquake ruptures related to the 2016 Mw 6.2 Amatrice earthquake and the uniquely dense seismological recordings provide an opportunity to understand better the processes controlling earthquake dynamics, strong ground motion, and the relation between earthquakes. We here propose a novel approach to design data-driven broadband (up to 5 Hz) dynamic rupture scenarios from 0.5-1 Hz Bayesian dynamic finite-fault inversion (Gallovič et al., 2019). We analyze the effects of enhancing the best-fitting smooth dynamic source inversion result by subsequent adding of complexity such as non-planar fault geometry (i.e., fault listricity and surface roughness), topography, inelastic off-fault rheology, and visco-elastic attenuation. We utilize the open-source software package SeisSol (www.seissol.org), suited explicitly for incorporating such geometrical complexities and high-resolution simulations performed on modern supercomputers. The obtained scenarios reproduce synthetics resembling the observations in terms of velocity and accelerations waveforms and Fourier-amplitude-spectra (FAS) up to 5 Hz. The simulated peak ground velocity (PGV) maps show de-amplification of ground motion amplitudes on the foot-wall and amplification on the hanging-wall as a consequence of the wave-focusing effect caused by the listric fault curvature. This effect is seen mainly for distances up to 10 km from the fault. Our study suggests that the complexity of the earthquake source should not be neglected for the seismic hazard assessment for regions adjacent to active faults.

Earth modeling is extraordinarily complex - and when the earth quakes, it’s no different. Earthquakes are highly non-linear and multiscale processes fracturing the Earth’s crust and emanating potentially destructive seismic waves. While computational seismology has been a pioneering field for high-performance computing, the multitude of scales and multi-physics character of earthquake source processes remain difficult to constrain.Earthquake science is increasingly data-rich, which opens up new pathways to synergistically integrate seismological, geodetic, tectonic and experimental analysis in multi-physics forward modeling. Using a physics-based description of earthquakes, interdisciplinary earthquake observations, modern numerical methods and hardware specific optimisation shed light on the dynamics, severity and cascading hazards of earthquake behaviour. An unparalleled degree of realism is enabled by exploiting high-performance computing.In this lecture, I will demonstrate the potential of Solid Earth community software for performing data-integrated, parsimonial scenarios of recent powerful multi-fault earthquake cascades, 3D fully-coupled Earth and ocean models of tsunami generated during earthquakes as well as cycles of earthquake and aseismic slip using petascale supercomputers. The inclusion of probabilistic and Bayesian frameworks, geometric transformations and diffuse interface approaches are future directions I will discuss for exploiting the expected exascale computing infrastructure.

With this contribution, we expand the discussion of effects that earthquakes induced by geo-energy projects can have on local communities, and that should probably be considered in future legislation or permitting processes. Inspired by consistent reports of felt and heard disturbances associated with the weeks-long stimulation of a 6-km-deep geothermal system in 2018 below the Otaniemi district of Espoo, Helsinki, we conduct numerical simulations of wave propagation in the solid earth and the atmosphere to assess the sensitivity of the ground shaking and audible noise patterns to various parameters. We explore the effects of three different local velocity models, realistic topography, variations of the source mechanism, and earthquake size on the loudness of the synthetic waves at frequencies up to 20 Hz, therefore reaching the lower limit of human sound sensitivity. We discuss the results of 18 elastic-acoustic coupled scenario simulations conducted on the Mahti high-performance computing infrastructure of the Finnish IT Center for Science CSC using the SeisSol wavefield solver. The computationally challenging simulations target the Otaniemi case study, i.e., we discretize a 12 km x 12 km x 15 km domain with a 2 km thick air layer over the solid earth domain. The earthquake point source is located at the 6.5 km deep location of the largest M1.8 event induced by the stimulation. In the target central area, we use a mesh with element lengths of about 14 m in the air and 97 m in the solid earth. Inside each element, we approximate the solution by a fifth-degree polynomial, by which we achieve a resolution of roughly 2.3 m in the air and 16 m in the earth. We develop an interactive visualization to facilitate instant access to the results governed by the different parameter combinations, where the synthetics are shown on top of a map of the Helsinki metropolitan region. This tool facilitates “what-if” analyses by quickly comparing the effects of fault orientation, source mechanism, and the velocity model. This supports effective communication of physics-based nuisance analysis to decision-makers and stakeholders, not only in environments such as the case study where there is little experience with natural earthquake phenomena. Together, these results resolve for the first time synthetic nuisance sound patterns at the 50 – 100 m scale in a densely populated capital region. The study highlights the mostly disregarded spatially variable audible effects that can negatively impact the public attitude towards geothermal stimulations, even if the ground shaking limits are safe, and it provides first estimates of the resources needed for comprehensive scenarios for future stimulation projects.

Seismica is an effort to establish a Diamond Open-Access (OA) journal for the community of researchers working in the (broadly defined) fields of seismology and earthquake science. Diamond OA journals are free to read, do not charge authors to publish, and thus promise to widen access to published research to all. Such efforts require broad community participation beyond editing and reviewing articles, as all functions typically fulfilled by paid staff, including administration, production, typesetting and copy editing, must be undertaken by volunteers.In December 2020, the Seismica Task Force, a spontaneously-organized group of seismologists and earthquake scientists, connected on Twitter. Inspired by the example of the established Diamond OA journal Volcanica, we began to explore the possibility of founding such a journal in our own field. Through outreach via social media, blog posts, conference presentations and disciplinary mailing lists, we have built a community of over 180 interested participants. With broad input, this group has developed a roadmap (https://doi.org/10.31223/X5304V) for the build-out of the journal, including an editorial structure and policies, broad outreach and structures to ensure a diverse editorial team, a logo and visual branding, and agreements with the McGill University Library to host and support the journal.In this presentation, we will introduce our first editorial board, and solicit our first article submissions for publication in 2022. We will also update the broader community on these and other developments in the journal-building process, and share our experiences and lessons learned.