SM8.1

Dehydration embrittlement was proposed to account for intermediate or deep earthquakes (e.g., Raleigh and Paterson, 1965). Many researchers have investigated the frictional instability induced by dehydration of hydrous minerals, such as gypsum (e.g., Milsch and Scholz, 2005; Brantut et al., 2011; Leclère et al., 2016). In addition, time dependence of dehydration of hydrous minerals has been studied based on reaction kinetics (e.g., Sawai et al., 2013). Since kinetics controls the dehydration rate, the effect of dehydration-derived pore fluid pressure on the mechanical strength of rocks can also be represented by kinetics. However, there is no experimental study to quantitatively investigate how pore fluid pressure builds up and controls the mechanical strength of fault gouges in terms of kinetics. Here, we derived time function of pore fluid pressure based on dehydration kinetics of simulated gypsum (bassanite) gouges. First, we conducted friction experiments of simulated gypsum gouges using gas apparatus under eight different conditions of pressures from 10 MPa to 200 MPa and temperatures from room temperature to 180 °C, spanning dehydration condition of gypsum. Each stress-strain curve showed stick-slip behaviors with almost constant stress drops and recurrence intervals depending on the effective pressures under the conditions of room temperature (RT): larger stress drops and longer intervals for higher effective stresses. On the other hand, stress drops and recurrence intervals gradually decrease with time under 200 MPa and 110 °C, close to the dehydration boundary. These results suggested that the elevated pore fluid pressure by dehydration decreases effective pressure and reduces the stress drops and the intervals. We tested this hypothesis as follows. Microstructural observations illuminated marked development of Riedel shears (R1 shear) in samples deformed under the stability field of gypsums (RT and 70 °C), while scarce development of Riedel shears in the sample deformed under 110 °C, being consistent with Leclère et al. (2016)’s observations on that the elevated pore pressure suppress the development of Riedel shears. Based on the equation of state for water (He and Zoller, 1991), we calculated the porosity of the sample deformed under 110 °C. Although the estimated value was smaller than that obtained from dehydration under hydrostatic conditions (Bedford et al., 2017), this result indicates that shear compaction may have occurred due to deformation caused by higher differential stress. Considering that the decrease in effective pressure modulates the amount of stress drops and recurrence intervals, we analyzed frictional coefficients with Mohr’s circle assuming pore fluid pressure. The estimated value of about 0.6 is consistent with Byerlee (1978)’s law. Based on the results, we created a time function for evolution of pore fluid pressure controlled by Avrami-type dehydration kinetics (Avrami, 1940). The estimated Avrami exponent, the important parameter for crystallization, of 3.121 indicated that the dehydration proceeded with nucleation and three-dimensional growth. This function enables more accurate prediction of pore fluid pressure evolution controlled by dehydration kinetics and may contribute to better understanding the effect of hydrous minerals on frequency of intermediate and deep earthquakes.

How to cite: Kawabata, M., Sasaki, Y., Iwasaki, M., Shiraishi, R., Muto, J., and Nagahama, H.: Time-varying stick-slip behaviors described by dehydration kinetics of gypsum, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11092, https://doi.org/10.5194/egusphere-egu22-11092, 2022.

Advances in modelling and access to InSAR and GNSS observations have highlighted the role that rheological heterogeneities play in postseismic deformation. Here we discuss three recent studies (Muto et al. 2019, Sambuddha et al. 2022, and Takada et al. in prep) following the 2011 Tohoku-Oki and 2008 Iwate-Miyagi earthquakes, which reveal both localised and along-strike rheological heterogeneities. We construct a self-consistent physical model of the postseismic deformation for these two events using the Unicycle code (Moore et al. 2019, Barbot, Moore, and Lambert 2017), with which we consider coupled fault slip and viscoelastic flow utilising laboratory-derived constitutive laws to simulate the time series of geodetic observations. All three studies illuminate a crustal low viscosity rheological heterogeneity in the vicinity of Mt Kurikoma / Mt Naruko. This is perhaps to be expected, given the proximity to known active volcanic centres, and is commensurate with observations following the 2016 Kumamoto earthquake (Moore et al. 2017) where we found low-viscosity anomalies beneath Mt Aso and Mt Kuju. However, the heterogeneities the data reveal are not restricted to known volcanic regions, because our results also suggest along-arc heterogeneity in the forearc mantle rheology of north-eastern Japan; specifically we find a narrower cold nose in the Miyagi region and wider for the Fukushima forearc. We also find evidence of interaction between the localized crustal heterogeneity and afterslip in both events, highlighting the importance of addressing mechanical coupling for long-term studies of postseismic relaxation. Variations in rheological properties in the lithosphere are not restricted to viscous and thermal effects, and observations of the Iwate-Miyagi earthquake suggest elastic heterogeneities may also play a role. We therefore conclude by presenting expressions for computing displacements and stress due to localised (faulting) and distributed inelastic deformation in heterogeneous elastic spaces with piece-wise constant homogeneous elastic subregions (Sato & Moore 2022), and their application in the context of the seismic cycle.

Muto J, Moore J D P, Barbot S, Iinuma T, Ohta Y, Horiuchi S, Hikaru I, 2019. Coupled afterslip and transient mantle flow after the 2011 Tohoku earthquake. Science Advances

Dhar S, Muto J, Ito Y, Muira S, Moore J D P, Ohta Y, Iinuma T, 2022. Along-Arc Heterogeneous Rheology Inferred from Postseismic deformation of the 2011 Tohoku-oki Earthquake.

Moore J D P, Barbot S, Feng L, Hang Y, Lambert V, Lindsey E, Masuti S, Matsuzawa T, Muto J, Nanjundiah P, Salman R, Sathiakumar S, & Sethi H, 2019. jdpmoore/unicycle: Unicycle. In Coupled afterslip and transient mantle flow after the 2011 Tohoku earthquake, Science Advances 2019. Zenodo. https://doi.org/10.5281/zenodo.5688288

Barbot S, Moore J D P, Lambert V, 2017. Displacements and stress associated with distributed anelastic deformation in a half-space. BSSA

Moore J D P, Yu H, Tang C, Wang T, Barbot S, Peng D, Masuti S, Dauwels J, Hsu Y, Lambert V, Nanjundiah P, Wei S, Lindsey E, Feng L, Shibazaki B, 2017. Imaging the distribution of transient viscosity after the 2016 Mw7.1 Kumamoto earthquake. Science

Sato D, Moore J D P, 2022. Displacements and stress associated with localised and distributed inelastic deformation with piecewise-constant elastic variations.

How to cite: Moore, J., Dhar, S., Muto, J., Sato, D., and Takada, Y.: The role of rheological heterogeneities in postseismic deformation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7627, https://doi.org/10.5194/egusphere-egu22-7627, 2022.

The triggering mechanism of earthquakes and their synchronization in time and space can be considered the two sides of the same coin. Our previous studies on earthquake triggering reveal sensitive parameters affecting the triggering mechanism using simple spring slider systems. We pursue our previous analyses by considering a simulation set-up for synchronizing three strong asperity patches on a vertically oriented strike-slip fault with initial slip heterogeneity separated by barriers and strong creeping regions at the edges. This analogy intends to explore earthquake synchronization in time and mimic observed sequences of large earthquakes that ruptured most of the North Anatolian Fault within short time intervals. Using the quasi-dynamic and full-dynamic pseudo-spectral Fast Fourier Transform (FFT) method, we apply a periodic fault model governed with Rate-and-State Friction (RSF) law embedded in a 2.5D continuum. Simulation results so far using the quasi-dynamic approach revealed that the earthquake synchronization is mainly affected by direct velocity effect parameters, barrier dimension/properties, and RSF law (aging and slip law), particularly the weakening terms. Lower direct velocity effect parameters, state evolutions with a stronger weakening term such as slip law, and shorter barrier lengths promote better synchronization. In this respect, we observed fast, slow, or no synchronization depending on the parameter sets. It is also worth noting that slip localizes in the continuum at small critical slip distances, which cannot be inferred from simple 1D models, suggesting the size dependence. In order to minimize inherent non-uniqueness and uncertainties, the same set-up will also be simulated with the full-dynamic approach in which wave-mediated stress transfer is taken into account, and the long-term earthquake histories will be correlated with case-specific simulations.

How to cite: Sopaci, E. and Özacar, A. A.: Do Large Earthquakes along Major Faults Synchronize in Time?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-508, https://doi.org/10.5194/egusphere-egu22-508, 2022.

Earthquakes often come in clusters formed of foreshock-mainshock-aftershock sequences. This clustering is generally thought to result from a cascading process which is commonly modeled using either the phenomenological ETAS model or a stress-based model assuming an earthquake nucleation process governed by Coulomb stress changes and Rate-and-State friction (CRS). In this work, we numerically investigated the foreshock and aftershock sequence in a discrete fault network with rate and state friction law and compared the result with the ETAS model. We set a fault zone consisting of dense fault segments and an off-fault area consisting of sparsely distributed smaller faults in the simulation domain. The CRS simulations are conducted 100 times with 1000 discrete faults with randomly generated fault location, initial velocity, and fault length within the weighted distribution, yielding a Gutenberg-Richter law. The simulations produce realistic foreshocks and aftershocks sequences. Aftershocks occur in the area of increased Coulomb stress and decay following Omori law as observed in nature. Individual foreshock sequences do not show a clear trend, but once stacked, they show an apparent inverse-Omori law acceleration. The prediction from our CRS model can be fitted with the ETAS model. This is not surprising since ETAS incorporates the Omori and Gutenberg-Richter laws. However, our CRS model predicts significantly more foreshocks than would be expected from the ETAS model. This results from the fact that the triggering productivity is lower in the aftershock sequence than in the foreshocks due to the depletion of critically stressed faults in our simulations. In other words, the ETAS is not compatible with the CRS model because Coulomb stress changes result in a time advance (if positive) or delay (if negative). This clustering process is fundamentally different from the additive process assumed in ETAS. As a result, the claim made that foreshocks more frequent than expected based on ETAS imply pre-seismic slip might be incorrect. It could alternatively be a manifestation of the nucleation process.

How to cite: Im, K. and Avouac, J.-P.: Numerical Modeling of Cascading Foreshocks and Aftershocks in Discrete Fault Network, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3110, https://doi.org/10.5194/egusphere-egu22-3110, 2022.

Simulations of sequences of earthquakes and aseismic slip (SEAS) including more than one fault, complex geometries and elastic heterogeneities are challenging. We present a symmetric interior penalty discontinuous Galerkin (SIPG) method accounting for the complex geometries and heterogeneity of the subsurface. The method accommodates two- and three-dimensional domains, is of arbitrary order, handles sub-element variations in material properties and supports isoparametric elements, i.e. high-order representations of the exterior and interior boundaries and interfaces including intersecting faults.

We provide an open-source reference implementation, Tandem, that utilises highly efficient kernels, is inherently parallel and well suited to perform high resolution simulations on large scale distributed memory architectures. Further flexibility is provided by optionally defining the displacement evaluation via a discrete Green's function, using algorithmically optimal and scalable sparse parallel solvers and preconditioners. We highlight the characteristics of the SIPG formulation via an extensive suite of verification problems (analytic, manufactured and code comparison) for elasto-static and seismic cycle problems. We demonstrate that high-order convergence of the discrete solution can be achieved in space and time for elasto-static and SEAS problems.

Lastly, we apply the method to realistic demonstration models consisting of a 2D SEAS multi-fault scenario on a shallowly-dipping normal fault with four curved splay faults, and a 3D multi-fault scenario of instantaneous displacement due to the 2019 Ridgecrest, CA, earthquake sequence. We exploit the curvilinear geometry representation in both application examples and elucidate the importance of accurate stresses (or displacement gradients) representations on-fault. Our results exploit advantages of both the boundary integral and volumetric methods and is an interesting avenue to pursue in the future for extreme scale 3D SEAS simulations.

How to cite: May, D., Uphoff, C., and Gabriel, A.-A.: A discontinuous Galerkin method for sequences of earthquakes and aseismic slip on multiple faults using unstructured curvilinear grids, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12166, https://doi.org/10.5194/egusphere-egu22-12166, 2022.

There is a growing interest in understanding how geologic faults respond to transient sources of fluid. However, the spatio-temporal evolution of sequences of seismic and aseismic slip in response to pore-fluid evolution is still poorly constrained. In this study, we present H-MEC (Hydro-Mechanical Earthquake Cycles), a newly-developed two-phase flow numerical code — which couples solid rock deformation and pervasive fluid flow — to simulate how crustal stress and fluid pressure evolve during the earthquake cycle on a fluid-bearing fault structure. This unified 2D numerical framework accounts for full inertial (wave) effects and fluid flow in a finite difference method and poro-visco-elasto-plastic compressible medium with rate-dependent strength. An adaptive time stepping allows the correct resolution of both long- and short-time scales, ranging from years to milliseconds during the dynamic propagation of dynamic rupture. We present a comprehensive plane strain strike-slip setup in which we test analytical benchmarks of pore-fluid pressure diffusion from an injection point. We then investigate how pore-fluid pressure evolution and solid–fluid compressibility control sequences of seismic and aseismic slip on a finite fault width. While the onset of fluid-driven shear cracks is controlled by localized collapse of pores and dynamic self-pressurization of fluids inside the undrained fault zone, subsequent dynamic ruptures are driven by solitary pulse-like fluid pressure wave propagating at seismic speed. Furthermore, shear strength weakening associated with rapid self-pressurization of pore-fluid can account for the slip–fracture energy scaling observed in large earthquakes. This numerical framework provides a viable tool to better understand fluid-driven dynamic ruptures — either as a natural process or induced by human activities — and highlight the importance of considering the realistic hydro-mechanical structure of faults to investigate sequences of seismic and aseismic slip.

How to cite: Dal Zilio, L., Hegyi, B., Behr, W., and Gerya, T.: Fluid-driven earthquake sequences and aseismic slip in a poro-visco-elasto-plastic fluid-bearing fault structure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6897, https://doi.org/10.5194/egusphere-egu22-6897, 2022.

Natural fault system observations feature complexity that includes damage variation from the outer damage zone to the fault core and associated rheological degradation (e.g. variation in the frictional strength and spatio-temporal slip localisation). In earthquake dynamic rupture simulations, faults are typically treated as infinitesimally thin interfaces with distinct on- versus off-fault rheologies. Commonly, such faults are explicitly represented in the discretisation of the computational domain.

Here we present a diffuse interface approach for dynamic rupture modelling. We introduce a 2D spectral element method (SEM) with an embedded smeared discontinuity representing volumetric fault slip. Our diffuse fault SEM is inspired by the stress-glut method of Andrews, 1999. In our approach, a subdomain in which the tangential stresses are limited by a critical shear strength and an empirical friction law is embedded in a purely elastic domain, resembling classical discrete fault representations. Our approach is implemented on a structured quadrilateral mesh within an SEM framework for elastic wave propagation, with PETSc (Balay et al. 2019) as a linear algebra back-end.

Our method collapses volumetric complexities onto a distribution within a compact support instead of the traditional interface approach, making it a flexible inelastic zone alternative for mesh-independent fault representation in dynamic rupture simulations. We conduct 2D numerical experiments, including a kinematically driven Kostrov-like crack and spontaneous dynamic rupture as defined in SCEC community benchmarks (Harris et al., 2018) of increasing complexity. We extract the spectral response from seismograms at different receivers normal and along the fault. We also analyse the capacity of flexible fault representation by including mesh-independent fault geometries. 

Our approach will allow us to incorporate volumetric failure rheologies in SEM dynamic rupture simulations and is part of the TEAR ERC project (www.tear-erc.eu).

How to cite: Hayek Valencia, J. N., May, D., Pranger, C., and Gabriel, A.-A.: Diffuse thick fault representation in 2D SEM for earthquake dynamic rupture simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12539, https://doi.org/10.5194/egusphere-egu22-12539, 2022.

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.

How to cite: Niu, Z., Gabriel, A.-A., May, D., Sens-Schönfelder, C., and Igel, H.: A Discontinuous-Galerkin approach to model non-classical nonlinearity observed from lab to global scales, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10523, https://doi.org/10.5194/egusphere-egu22-10523, 2022.

The response of gravity retaining walls during ground motion is still a challenging field. Recent developments in computational methods have opened the possibility of enhancing the understanding of the non-linear nature of soil-structure systems, e.g., earth pressure thrust acting on the retaining wall, translational and rotational movements, propagation of waves in the soil more realistically and quickly. Till today, Mononobe Okabe (MO) method (pseudo-static) is the most used analytical method because of its simplicity. However, there are many limitations and gives over-conservative results in terms of earth pressure thrust, and many literatures have already justified such a response. Several improved studies are already available, but very few have considered proper soil-structure interaction, real-time input earthquake data (not sinusoidal), and a sufficient number of earthquakes to evaluate the response acting on the wall during dynamic loading.

We seek contribution by analyzing the problem numerically using FE software Plaxis 2D and studying the behavior of retaining wall during seismic loading (range of a_max = 0.053g to 1.2g) in terms of acceleration, displacement, rotation, and earth pressure thrust of retaining wall. The main contribution observed is the acceleration was not uniform throughout the medium instead gets amplified up to around 0.6g and later gets attenuated with maximum amplification occurring at the top of the retaining wall followed by the top of backfill soil and base of the wall. The residual displacement and rotation showed an incremental trend with an increase in horizontal seismic coefficient (k_h). The earth pressure thrust obtained using numerical analysis was comparatively less than predicted by the MO method.

Keywords: Gravity retaining wall; Acceleration amplification response; Earth pressure thrust; Finite element method; 

How to cite: Singh, P., Bhartiya, P., Chakraborty, T., and Basu, D.: Numerical Advances in Understanding the Behavior of Gravity Retaining Wall during Seismic Motions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-349, https://doi.org/10.5194/egusphere-egu22-349, 2022.

Acoustic wave equations are widely employed in wavefield extrapolation and inversion due to their simplicity compared to the elastic wave equations. In anisotropic media, qP- and qSV-waves are coupled. Multiple acoustic approximations in the vertical transversely isotropic (VTI) media have been proposed during the last decades. A classic way is to set the vertical S-wave velocity zero. As such, the S-wave artefacts still exist, whose amplitude increases with anisotropy. Setting S-wave velocity zero in all propagating directions tackles the issue. However, the higher-order spatial derivatives in the pure qP-wave equation make it hard to solve in the space domain. The spatial derivatives in the denominator of the pure qP-wave equation make the solution by the spatial-domain finite-difference unstable.  In this study, we employed the time-domain pseudospectral method to solve both the classic acoustic wave equation and the pure qP-wave equation in VTI media. Hybrid absorbing boundary conditions are used. Both equations are applied to reverse time migration (RTM) for the anisotropic Marmousi model. The new qP-wave equation outperformed the classic qP-wave equation regarding the computational time. Further work can be extended to waveform inversion with the pure qP-wave equation.

How to cite: Zhang, Y., De Siena, L., and Kaus, B.: Simulation of pure qP-wave in vertical transversely isotropic media, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5432, https://doi.org/10.5194/egusphere-egu22-5432, 2022.

We investigate theoretical limits to detection of fast and slow seismic events and discuss spatial variations of ground motion expected from an synthetic family of M6 earthquakes at short epicentral distances. The performed analyses are based on synthetic velocity seismograms calculated with the discrete wavenumber method assuming seismic velocities and attenuation properties of the crust in Southern California. The examined source properties include  magnitudes ranging from M -1.0 to M 6.0, static stress drops (0.1-10 MPa), and slow and fast ruptures (0.1-0.9 of shear wave velocity). For the M 6.0 events we also consider variations in rise times producing crack- and pulse-type events and different rupture directivities. We found slow events produce ground motions with considerably lower amplitude than corresponding regular fast earthquakes with the same magnitude, and hence are significantly more difficult to detect. The static stress drop and slip rise time also affect the maximum radiated seismic motion, and thus event detectability. Apart from geometrical factors, the saturation and depletion of seismic ground motion at short epicentral distances stem from radiation pattern, earthquake size (magnitude, stress drop), and rupture directivity. The rupture velocity, rise time and directivity affect significantly the spatial pattern of the ground motions. The results can help optimizing detection of slow and fast dynamic small earthquakes and understand the spatial distribution of ground motion generated by large events.

How to cite: Kwiatek, G. and Ben-Zion, Y.: Detection Limits and Near-Field Ground Motions of Fast and Slow Earthquakes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3555, https://doi.org/10.5194/egusphere-egu22-3555, 2022.

The seismic risk in France, a region of low to moderate seismicity, is of paramount importance given the large number of industrial and nuclear installations. However, the large uncertainties on the geology and the poor knowledge of active faults make the seismic hazard estimation a challenging task. Despite being a promising tool to explore the underlying uncertainties, numerical simulations must be duly calibrated by reproducing specific events.

In this work, we considered the 2019 Mw4.9 earthquake that occurred at Le Teil village in southern France. This event was recorded by 17 stations of 3-component accelerometers, within an area of 50 km around the epicenter (French Accelerometric Network). We used these records to calibrate the numerical simulation. The seismological P- and S-wave speed profiles used result from a 3D weighted average model for Metropolitan France. In addition, the topography was included in the spatial discretization. The uncertainties on dip, strike, and rake angles were explored in order to calibrate the far-field synthetic ground motion model by determining the eigenquakes that efficiently span a large diversity of sources.

A good agreement between synthetic and recorded time histories was found, despite the simplicity of the geological and source model.

How to cite: Lehmann, F., Gatti, F., Bertin, M., and Clouteau, D.: First calibration of the physics-based ground motion model of the 2019 Mw4.9 Le Teil earthquake (France), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7558, https://doi.org/10.5194/egusphere-egu22-7558, 2022.

The south-eastern part of Adriatic Sea is seismically highly active region where numerous strong events have occurred in historic times. Among these, the most significant is the infamous Great Dubrovnik earthquake of 1667. This event, whose magnitude was estimated to be in the vicinity of Mw 7.0, caused widespread devastation in the whole region. More recently, a large Mw 7.1 event happening in 1979 in Montenegro caused extensive damage along 100 km of coastline, including the area around Dubrovnik. From this it is obvious that the city of Dubrovnik is seismically highly vulnerable and that there is an acute need to better understand possible consequences if an event of such a magnitude would happen today.  
 
One of the major steps in reducing the seismic risk in any region is to simulate seismic shaking and to evaluate expected ground motion for plausible earthquake scenarios. Therefore, our aim in this work is to create several earthquake scenarios for the city of Dubrovnik and estimate seismically most endangered parts of the region. For that purpose, we first assemble a detailed 3D crustal model which includes information on physical parameters of interest (velocity and density) and which reflects all the important geological features of the studied area. Then, we test whether the model is suitable for simulation by computing and comparing broadband seismograms against the recorded data of several moderate events. We validate the results by assessing the goodness of fit for different metrics describing ground-motion. Next, by combining seismic and geophysical data, we define the geometry of the main active faults and parameters required for the rupture model used in the simulation. We calculate synthetic waveforms on a dense grid and then extract intensity measures to determine the expected ground-motion features of a strong seismic event such was The Great Dubrovnik earthquake.

How to cite: Latečki, H., Sečanj, M., Dasović, I., and Stipčević, J.: Seismic shaking scenarios for city of Dubrovnik, Croatia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8291, https://doi.org/10.5194/egusphere-egu22-8291, 2022.

Dynamic rupture modeling represents a preferable physics-based approach to strong ground motion simulations. However, its application in a broad frequency range (0-10Hz), interesting for engineering studies, is challenging. The main reason is that relatively simple models with smooth distributions of initial stress and frictional parameters on planar faults result in ground motions with depleted high-frequency content. Several studies suggested that nonplanar rupture surfaces can solve this issue. Nevertheless, fully accounting for rough ruptures typically requires supercomputers, preventing widespread use.

Here we test an efficient approach for the linear slip-weakening friction model on planar fault, based on the Ide and Aochi (2005) multiscale model, with a small-scale fractal distribution of the slip-weakening distance Dc. To intensify the incoherence of the rupture propagation, we also include a variation of the strength and initial stress correlated with Dc. We propose a way to combine the fractal variations of the dynamic parameters with a large-scale dynamic model. The planar fault assumption permits the use of the computationally very fast code FD3D_TSN (Premus et al., 2020). 

We illustrate the approach on a canonical elliptical model with linearly increasing fracture energy (i.e., constant rupture velocity) and the 2016 Mw6.2 Amatrice earthquake smooth rupture model from the dynamic source inversion by Gallovič et al. (2019). We demonstrate that the addition of the small-scale fractal properties results in sustained high-frequency radiation during the rupture propagation and omega-square (apparent) source time functions. The model improves the fit of the recordings of the Amatrice earthquake in the frequency range of 0-10Hz and generates synthetics agreeing with ground motion prediction equations up to 5Hz.

Our FD3D_TSN takes about 5 minutes to simulate the Mw6.2 rupture propagation on a single GPU. Nevertheless, the fractal dynamic model can be easily implemented in any dynamic rupture propagation code. This makes the proposed approach readily applicable in physics-based ground motion predictions for scenario earthquakes in seismic hazard assessment.

How to cite: Gallovič, F. and Valentová, Ľ.: Broadband strong ground motion modeling using planar dynamic rupture model with fractal parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8698, https://doi.org/10.5194/egusphere-egu22-8698, 2022.

We cross validate a numerical solver for wave propagation in 3-D elastic media written on Graphical Processing Units (GPUs) against the semi-analytical solver for earthquakes in axisymmetric media, using seismic full moment tensors as earthquakes sources, variable earthquake source durations, and comparing observed with synthetic seismograms. The GPU-based solver is based on a numerical formulation of elastodynamic wave equation and can capture isotropic and anisotropic media. The algorithm simulates wave propagation in elastic media in three dimensions and at very high spatial and temporal resolution, and can compute entire wavefields within seconds (Alkhimenkov et al., 2021). For example, the multi-GPU code for elastic wave propagation can compute the entire wavefield of a 1000^3 model (1 billion grid cells) in 40 seconds. We achieve a close-to-ideal parallel efficiency (98% and 96%) on weak scaling tests up to 128 GPUs by overlapping MPI communication and computations. Seismic full moment tensors are routinely used to model a range of seismic processes, natural and anthropogenic, including earthquakes (shear slip), volcanic events, explosions, cavity collapses, landslides, etc. The analytical solver is based on a Thompson-Haskell propagator matrix for layered axisymmetric media (Zhu and Rivera, 2002), with moment tensors as seismic sources, with seismic sources at depths 10s of km below the surface and seismic stations at distances over 2000 km, and has been successfully used in various earthquake source studies (e.g. Alvizuri et al 2018). We validate the GPU-based wave propagation solver through numerical experiments in homogeneous and in layered media, and with observed and synthetic seismograms for an M4.6 earthquake in Linthal, Switzerland on 2017-03-06 with seismic stations at distances up to 30 km. The seismograms from the numerical solver match the analytic and observed seismograms (within frequencies 0.02-0.10 Hz). In future work we will apply the solver to study earthquake source generation, wave propagation in anisotropic media, and seismic source determination.

References
Alkhimenkov, Y., Räss, L., Khakimova, L., Quintal, B., & Podladchikov, Y., 2021. Resolving wave propagation in anisotropic poroelastic media using graphical processing units (CPUs), J. Geophys. Res., 126, doi:10.1029/2020JB021175.
Alvizuri, C., Silwal, V., Krischer, L., & Tape, C., 2018. Estimation of full moment tensors, including uncertainties, for nuclear explosions, volcanic events, and earthquakes, J. Geophys. Res. Solid Earth, 123, 5099–5119, doi:10.1029/2017JB015325.
Zhu, L. & Rivera, L. A., 2002. A note on the dynamic and static displacements from a point source in multilayered media, Geophys. J. Int., 148, 619–627, doi:10.1046/j.1365-246X.2002.01610.x.

How to cite: Alvizuri, C., Alkhimenkov, Y., and Podladchikov, Y.: Cross-validation of a GPU-based wave propagation solver and application to seismic waveform modeling of an M4.6 earthquake in Linthal, Switzerland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11592, https://doi.org/10.5194/egusphere-egu22-11592, 2022.