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We investigate similarities and differences between natural and simulated slow earthquakes using nonlinear dynamical system tools. We use spatio‐temporal slip potency rate data derived from Global Navigation Satellite System (GNSS) position time series in the Cascadia subduction zone and numerical simulations intended to reproduce their pulse‐like behavior and scaling laws. We provide metrics to evaluate the accuracy of simulations in mimicking slow earthquake dynamics. We investigate the influence of spatio‐temporal coarsening as well as observational noise. Despite the use of many degrees of freedom, numerical simulations display a surprisingly low average dimension, akin to natural slow earthquakes. Instantaneous dynamical indices can reach large values (>10) instead, and differences persist between numerical simulations and natural observations. We propose to use the suggested metrics as an additional tool to narrow the divergence between slow earthquake observations and dynamical simulations. Plain Language Summary: Earthquakes are natural phenomena resulting from the Earth's crust cyclically loading and unloading. The unpredictability of seismic events, combined with the large energy they release during the co‐seismic phase, poses not only scientific challenges but also significant threats to numerous populated regions at risk. Numerical simulations of the seismic cycle are widely used to better understand the dynamics of this natural phenomenon. Nonetheless, a direct comparison of earthquake observations and numerical simulations of the seismic cycle is currently prevented by the lengthy recurrence time of large seismic events rupturing the same fault segment and the short observational record at our disposal. Slow earthquakes, exhibiting lower recurrence times, serve as a viable alternative for validating models against real‐world observations. We investigate similarities and differences between natural and simulated slow earthquakes through the lens of nonlinear dynamical system theory. We study the effects of observational noise and spatio‐temporal coarsening putting the simulations in conditions like real‐world observations. We find that observational noise does not suffice to explain the higher complexity retrieved for natural observations. By refining our understanding of these dynamical systems, this study contributes to advancements in seismic research, offering a picture of the complexities involved on active faults. Key Points: Natural observations and numerical simulations of slow earthquakes share common average dynamical propertiesNatural observations show higher complexity than numerical simulationsMatching instantaneous dynamical properties can help reducing the discrepancies between natural and simulated slow earthquakes [ABSTRACT FROM AUTHOR]

The fast increase of convergence rate between India and Eurasia around 65 million years ago (Ma)-from approximately 8 cm yr -1 to a peak rate of approximately 18 cm yr -1 -remains a complex geological event to explain 1-8 , given the inherent uncertainty surrounding the tectonic history and the intricate interplay of forces influencing plate speed 9-11 . Here we use a combination of geochemical analysis and geodynamic modelling to propose that this rapid convergence can be explained by sediment subduction derived from the northern Indian passive margin. Through isotope and trace element analysis, we find an enhanced contribution of terrigenous sediment melt to the mantle source of the Gangdese magmatic rocks around 65 Ma, concurrent with the acceleration of India-Eurasia convergence. Numerical experiments suggest that subduction of sediments more than 1 km thick covering an approximately 1,000-km-wide ocean basin abutting the northern Indian passive margin starting from 65 Ma could have spurred the increased convergence rate and further led to significant crustal extension, consistent with empirical observations. Our study implies that the acceleration of India-Eurasia convergence marks the arrival of passive-margin-derived sediments, constraining the initial India-Eurasia collision to be around 60 Ma. It further suggests that temporary accelerations in subduction rates might be a common feature at the final stage of continental assembly., (© 2024. The Author(s).)

The 2023 M7.8 and M7.5 earthquake doublet near Kahramanmaraş, Turkey, provides insight regarding how large earthquakes rupture complex faults. Here we determine the faults geometry using surface ruptures and Synthetic Aperture Radar measurements, and the rupture kinematics from the joint inversion of high-rate Global Navigation Satellite System (GNSS), strong-motion waveforms, and GNSS static displacement. The M7.8 event initiated on a splay fault and subsequently propagated along the main East Anatolian Fault with an average rupture velocity between 3.0 and 4.0 km/s. In contrast, the M7.5 event demonstrated a bilateral supershear rupture of about 5.0-6.0 km/s over an 80 km length. Despite varying strike and dip angles, the sub-faults involved in the mainshock are nearly optimally oriented relative to the local stress tensor. The second event ruptured a fault misaligned with respect to the regional stress, also hinting at the effect of local stress heterogeneity in addition to a possible free surface effect., (© 2024. The Author(s).)

Earthquakes are rupture-like processes that propagate along tectonic faults and cause seismic waves. The propagation speed and final area of the rupture, which determine an earthquake's potential impact, are directly related to the nature and quantity of the energy dissipation involved in the rupture process. Here, we present the challenges associated with defining and measuring the energy dissipation in laboratory and natural earthquakes across many scales. We discuss the importance and implications of distinguishing between energy dissipation that occurs close to and far behind the rupture tip, and we identify open scientific questions related to a consistent modeling framework for earthquake physics that extends beyond classical Linear Elastic Fracture Mechanics., (© 2024. The Author(s).)

We combined novel laboratory techniques and numerical modeling to investigate (a)seismic preparatory processes associated with deformation localization during a triaxial failure test on a dry sample of Berea sandstone. Laboratory observations were quantified by measuring strain localization on the sample surface with a distributed strain sensing (DSS) array, utilizing optical fibers, in conjunction with both passive and active acoustic emission (AE) techniques. A physics-based computational model was subsequently employed to understand the underlying physics of these observations and to establish a spatio-temporal correlation between the laboratory and modeling results. These simulations revealed three distinct stages of preparatory processes: (i) highly dissipative fronts propagated towards the middle of the sample correlating with the observed acoustic emission locations; (ii) dissipative regions were individuated in the middle of the sample and could be linked to a discernible decrease of the P-wave velocities; (iii) a system of conjugate bands formed, coalesced into a single band that grew from the center towards the sample surface and was interpreted to be representative for the preparation of a weak plane. Dilatative lobes at the process zones of the weak plane extended outwards and grew to the surface, causing strain localization and an acceleration of the simulated deformation prior to failure. This was also observed during the experiment with the strain rate measurements and spatio-temporally correlated with an increase of the seismicity rate in a similar rock volume. The combined approach of such laboratory and numerical techniques provides an enriched view of (a)seismic preparatory processes preceding the mainshock., Competing Interests: Conflict of interestThe authors have no conflict of interest to declare that are relevant to the content of this article., (© The Author(s) 2024.)

Recent studies have shown that the Himalayan region is under the threat of earthquakes of magnitude nine or larger. These estimates are based on comparisons of the geodetically inferred moment deficit rate with the seismicity of the region. However, these studies did not account for the physics of fault slip, specifically the influence of frictional barriers on earthquake rupture dynamics, which controls the extent and therefore the magnitude of large earthquakes. Here we combine an improved probabilistic estimate of moment deficit rate with results from dynamic models of the earthquake cycle to more fully assess the seismogenic potential of the Main Himalayan Thrust (MHT). We propose a straightforward and efficient methodology for incorporating outcomes of physics-based earthquake cycle models into hazard estimates. We show that, accounting for uncertainties on the moment deficit rate, seismicity and earthquake physics, the MHT is prone to rupturing in M w 8.7 earthquakes every T  > 200 years., (© 2021. The Authors.)