Towards a unified framework for modeling fault zone evolution: From particles comminution to secondary faults branching

The brittle portion of the crust contains structural features such as faults, jogs, joints, bends, and cataclastic zones that span a wide range of length scales. These features may have a profound effect on earthquake nucleation, propagation, and arrest. Incorporating these existing features in modeling and the ability to spontaneously generate new one in response to earthquake loading is crucial for predicting seismicity patterns, distribution of aftershocks and nucleation sites, earthquakes arrest mechanisms, and topological changes in the seismogenic zone structure. Here, we report on our efforts in modeling two important mechanisms contributing to the evolution of fault zone topology: (i) Grain comminution at the submeter scale, and (ii) Secondary faults generation at the scale of few to hundreds of meters. We model grain comminution within the framework of Shear Transformation Zone theory, a nonequilibrium statistical thermodynamic framework for modeling plastic deformation in amorphous materials. We postulate, based on energy balance, an equation for the grain size reduction as a function of the applied work rate and pressure. We show that grain breakage is a potential weakening mechanism at high strain rate. It promotes strain localization and may explain the long-term persistence of shear bands in natural faults. To model secondary faults generation we developed a nested fault scheme using the finite element software PyLith. As the dynamic rupture propagates on the main fault the stress state changes and eventually the off-fault shear stress is high enough to overcome the pressure-dependent rock strength defined by the Mohr–Coulomb failure envelope. If the Mohr–Coulomb failure criterion is satisfied, a new secondary fault is generated. The angle of the secondary fault with respect to the main fault is taken to be equal to the angle of the critical shear plane. This procedure is repeated until there is no need to add new faults (i.e., stresses everywhere are below the failure threshold). The secondary faults relax the medium contributing to slip and energy partitioning. They also lead to wave diffraction, slip heterogeneity, and slowing down of the rupture on the main fault. They provide potential nucleation site for future ruptures promoting complexity in earthquake cycle simulation. Under repeated earthquake ruptures, regions in the vicinity of primary slip surfaces become heavily fragmented. These regions are modeled using STZ theory. Incorporating the microscale granular model within the macroscopic finite element simulation provide a physics-based multiscale description for damage accumulation. The model provides insight into the dynamic evolution of fault zone topology coupled within the different phases of the seismic cycle. This is crucial for better evaluation of seismic hazard and risk

A systematic review and meta-analysis of the impact of the left atrial appendage closure on left atrial function.

BACKGROUND: Left atrial (LA) appendage closure (LAAC) is effective in patients with atrial fibrillation who are not candidates for long-term anticoagulation. However, the impact of LAAC on LA function is unknown. The aim of this study is to evaluate the impact of LAAC on atrial function. METHODS: This meta-analysis was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A search strategy was designed to utilize PubMed/Medline, EMBASE, and Google scholar for studies showing the effect of LAAC on the LA function from inception to November 20, 2021. The standardized mean difference (SMD) was calculated from the means and standard deviations. RESULTS: Of 247 studies initially identified, 8 studies comprising 260 patients were included in the final analysis. There was a significant increase in LA emptying fraction following LAAC compared with preoperative function (SMD: 0.53; 95% confidence interval [CI]: 0.04-1.01; p = .03; I2  = 75%). In contrast, there were no significant differences in LA volume (SMD: -0.07; 95% CI: -0.82-0.69; p = .86; I2  = 92%) peak atrial longitudinal strain (SMD: 0.50; 95% CI: -0.08-1.08; p = .09; I2  = 89%), peak atrial contraction strain (SMD: 0.38; 95% CI: -0.22-0.99; p = .21; I2  = 81%), strain during atrial contraction (SMD: -0.24; 95% CI: -0.61-0.13; p = .20; I2  = 0%), strain during ventricular systole (SMD: 0.47; 95% CI: -0.32-1.27; p = .24; I2  = 89%), strain during ventricular diastole (SMD: 0.09; 95% CI: -0.32-0.51; p = .66; I2  = 65%). CONCLUSION: LAAC is associated with improvement in the left atrial emptying fraction, but did not significantly influence other parameters

Community Code Verification Exercise for Simulating Sequences of Earthquakes and Aseismic Slip (SEAS)

Numerical simulations of sequences of earthquakes and aseismic slip (SEAS) have made great progress over past decades to address important questions in earthquake physics. However, significant challenges in SEAS modeling remain in resolving multiscale interactions between earthquake nucleation, dynamic rupture, and aseismic slip, and understanding physical factors controlling observables such as seismicity and ground deformation. The increasing complexity of SEAS modeling calls for extensive efforts to verify codes and advance these simulations with rigor, reproducibility, and broadened impact. In 2018, we initiated a community code‐verification exercise for SEAS simulations, supported by the Southern California Earthquake Center. Here, we report the findings from our first two benchmark problems (BP1 and BP2), designed to verify different computational methods in solving a mathematically well‐defined, basic faulting problem. We consider a 2D antiplane problem, with a 1D planar vertical strike‐slip fault obeying rate‐and‐state friction, embedded in a 2D homogeneous, linear elastic half‐space. Sequences of quasi‐dynamic earthquakes with periodic occurrences (BP1) or bimodal sizes (BP2) and their interactions with aseismic slip are simulated. The comparison of results from 11 groups using different numerical methods show excellent agreements in long‐term and coseismic fault behavior. In BP1, we found that truncated domain boundaries influence interseismic stressing, earthquake recurrence, and coseismic rupture, and that model agreement is only achieved with sufficiently large domain sizes. In BP2, we found that complexity of fault behavior depends on how well physical length scales related to spontaneous nucleation and rupture propagation are resolved. Poor numerical resolution can result in artificial complexity, impacting simulation results that are of potential interest for characterizing seismic hazard such as earthquake size distributions, moment release, and recurrence times. These results inform the development of more advanced SEAS models, contributing to our further understanding of earthquake system dynamics

Research on information systems failures and successes: Status update and future directions

The final publication is available at Springer via http://dx.doi.org/10.1007/s10796-014-9500-yInformation systems success and failure are among the most prominent streams in IS research. Explanations of why some IS fulfill their expectations, whereas others fail, are complex and multi-factorial. Despite the efforts to understand the underlying factors, the IS failure rate remains stubbornly high. A Panel session was held at the IFIP Working Group 8.6 conference in Bangalore in 2013 which forms the subject of this Special Issue. Its aim was to reflect on the need for new perspectives and research directions, to provide insights and further guidance for managers on factors enabling IS success and avoiding IS failure. Several key issues emerged, such as the need to study problems from multiple perspectives, to move beyond narrow considerations of the IT artifact, and to venture into underexplored organizational contexts, such as the public sector. © 2014 Springer Science+Business Media New York

Community Code Verification Exercise for Simulating Sequences of Earthquakes and Aseismic Slip (SEAS)

Numerical simulations of sequences of earthquakes and aseismic slip (SEAS) have made great progress over past decades to address important questions in earthquake physics. However, significant challenges in SEAS modeling remain in resolving multiscale interactions between earthquake nucleation, dynamic rupture, and aseismic slip, and understanding physical factors controlling observables such as seismicity and ground deformation. The increasing complexity of SEAS modeling calls for extensive efforts to verify codes and advance these simulations with rigor, reproducibility, and broadened impact. In 2018, we initiated a community code‐verification exercise for SEAS simulations, supported by the Southern California Earthquake Center. Here, we report the findings from our first two benchmark problems (BP1 and BP2), designed to verify different computational methods in solving a mathematically well‐defined, basic faulting problem. We consider a 2D antiplane problem, with a 1D planar vertical strike‐slip fault obeying rate‐and‐state friction, embedded in a 2D homogeneous, linear elastic half‐space. Sequences of quasi‐dynamic earthquakes with periodic occurrences (BP1) or bimodal sizes (BP2) and their interactions with aseismic slip are simulated. The comparison of results from 11 groups using different numerical methods show excellent agreements in long‐term and coseismic fault behavior. In BP1, we found that truncated domain boundaries influence interseismic stressing, earthquake recurrence, and coseismic rupture, and that model agreement is only achieved with sufficiently large domain sizes. In BP2, we found that complexity of fault behavior depends on how well physical length scales related to spontaneous nucleation and rupture propagation are resolved. Poor numerical resolution can result in artificial complexity, impacting simulation results that are of potential interest for characterizing seismic hazard such as earthquake size distributions, moment release, and recurrence times. These results inform the development of more advanced SEAS models, contributing to our further understanding of earthquake system dynamics

Earthquake nucleation and propagation on rate and state faults: single versus two state variables formulation and evolution by Kato–Tullis law

Earthquake nucleation and propagation has been studied extensively within the framework of single rate and state formulation with either the aging or the slip evolution laws. In this presentation we report on our ongoing work on simulating earthquake cycles on faults described by the two state variables formulation of the rate and state law. Beside the slip and aging evolution law we also consider the composite state law proposed by Kato and Tullis [2001]. The two state formulation has been found to provide a closer description of the observed relaxations following jumps over a wide range of sliding speeds. Gu and Rice (1984) have also shown through a quasi-static stability analysis that the two state formulation may lead to chaotic vibrations for a range of wavenumbers and slip rates. Meanwhile, compared to the slip and aging laws, the composite law matches better the observations in both the slide-hold-slide experiments and the velocity stepping tests. We use the Spectral Boundary Integral Equation method [Lapusta et al., 2000] to simulate ruptures on 2D antiplane faults embedded in an elastic full space. We show that nucleation using the composite law is very similar to nucleation using slip law. There are differences in the cycle simulation results between the two laws, however. The two state variables formulation, compared with the single state one, is found to lead to a richer dynamic response with more complex instability patterns. Our investigation will enable us to quantitatively determine the influence of using different friction and evolution laws on the details of the different phases of the seismic cycle

A hybrid finite element‐spectral boundary integral approach: Applications to dynamic rupture modeling in unbounded domains

The finite element method (FEM) and the spectral boundary integral method (SBI) have both been widely used in the study of dynamic rupture simulations along a weak interface. In this paper, we present a hybrid method that combines FEM and SBI through the consistent exchange of displacement and traction boundary conditions, thereby benefiting from the flexibility of FEM in handling problems with nonlinearities or small-scale heterogeneities and from the superior performance and accuracy of SBI. We validate the hybrid method using a benchmark problem from the Southern California Earthquake Center's dynamic rupture simulation validation exercises.We further demonstrate the capability and computational efficiency of the hybrid scheme for resolving off-fault heterogeneities by studying a 2D in-plane shear crack in two different settings: one where the crack is embedded in a high-velocity zone and another where it is embedded in a low-velocity zone. Finally, we discuss the potential of the hybrid method for addressing a wide range of problems in geophysics and engineering

Anatomy of Strike Slip Fault Tsunami-genesis

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

A Continuum Robot for Remote Applications: From Industrial to Medical Surgery With Slender Continuum Robots

The maintenance of critical industrial components is often hindered by limited access, tortuous passages, and complex geometries. In highly constrained environments, inspection tasks are currently performed with borescopes, but even skilled operators struggle with hard-to-reach targets, and the limited mobility prevents in situ repair when defects are identified. Thanks to an active shape control, snakelike and continuum robots can outperform borescopes for short-range inspection as well as enable intervention. However, their actuation technology limits their scalability in length, as longer bodies pose control challenges due to their intrinsically low stiffness and space constraints. To overcome the limitations of both borescopes and continuum robots, here, we propose a modular design at their intersection, with both active tendon-driven and passively flexible segments. The main elements of the novel design, including the actuation and control interface, are described, and the system is demonstrated in scenarios for aerospace assets, nuclear installations, and robotassisted surgery