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Gromov ground state in phase space engineering for fusion energy

Physical Review E (Plasma physics) - Wed, 02/19/2025 - 10:00

Author(s): Hong Qin, Elijah J. Kolmes, Michael Updike, Nicholas Bohlsen, and Nathaniel J. Fisch

Phase space engineering by rf waves plays important roles in both thermal D-T fusion and nonthermal advanced fuel fusion, but not all phase space manipulation is allowed; certain fundamental limits exist. In addition to Liouville's theorem, which requires the manipulation to be volume preserving, Gr…

[Phys. Rev. E 111, 025205] Published Wed Feb 19, 2025

Tidal correlation of deep tectonic tremors increases during long-term slow slip events in the Bungo Channel, southwest Japan

Earth,Planets and Space - Wed, 02/19/2025 - 00:00

Relocating seismic events in the North Sea: challenges and insights for earthquake analysis

Geophysical Journal International - Wed, 02/19/2025 - 00:00

SummaryIn this paper, we present a catalogue of relocated seismic events in the North Sea spanning 1961 to 2022. Data from all relevant agencies were combined, incorporating all available seismic phase readings, thereby enhancing station coverage. As a result, our updated locations reveal a more clustered and aligned seismicity pattern compared with the original catalogue. Even with our combined dataset, only 157 of the 7,089 relocated events have azimuthal gaps of less than 90 degrees. Additionally, the distances between onshore stations and offshore events are considerable. Both of these factors lead to relatively poorly constrained hypocentres for most events. We therefore evaluate the performance of 1D velocity models routinely used by different North Sea adjacent monitoring agencies for earthquake location estimations in the North Sea. The variations in assessments due to the seismic velocity model used are significantly larger than the uncertainty ellipses calculated in the relocation, demonstrating that arithmetic uncertainties systematically underestimate location uncertainties in this setting. Obtaining a realistic estimate of location uncertainty is however crucial, particularly for distinguishing between natural and induced seismicity. This is fundamental to safe monitoring of the North Sea offshore industries, including geological CO2 storage. To overcome these discrepancies between the uncertainty ellipses and our multiple relocations, we introduce an alternative method that accounts for variability in the 1D velocity models. This approach enhances the reliability of the earthquake catalogue, and provides a more robust assessment of seismic activity in the North Sea.

Bayesian Full Waveform Inversion of Surface Waves with Annealed Stein Variational Gradient Descent

Geophysical Journal International - Wed, 02/19/2025 - 00:00

SummaryElastic full-waveform inversion has recently been utilized to estimate the physical properties of the upper tens of meters of the subsurface, leveraging its capability to exploit the complete information contained in recorded seismograms. However, due to the non-linear and ill-posed nature of the problem, standard approaches typically require an optimal starting model to avoid producing non-physical solutions. Additionally, conventional optimization methods lack a robust uncertainty quantification, which is essential for subsequent informed decision-making.Bayesian inference offers a framework for estimating the posterior probability density function through the application of Bayes’ theorem. Methods based on Markov Chain Monte Carlo processes use multiple sample chains to quantify and characterize the uncertainty of the solution.However, despite their ability to theoretically handle any form of distribution, these methods are computationally expensive, limiting their usage in large-scale problems with computationally expensive forward modelings, as in the case of full-waveform inversion. Variational Inference provides an alternative approach to estimating the posterior distribution through a parametric or non-parametric proposal distribution. Among this class of methods, Stein Variational Gradient Descent stands out for its ability to iteratively refine a set of samples, usually referred to as particles, to approximate the target distribution through an optimization process. However, mode and variance-collapse issues affect this approach when applied to high-dimensional inverse problems.To address these challenges, in this work we propose to utilize an annealed variant of the Stein Variational Gradient Descent algorithm and apply this method to solve the elastic full-waveform inversion of surface waves. We validate our proposed approach with a synthetic test, where the velocity model is characterized by significant lateral and vertical velocity variations. Then, we invert a field dataset from the InterPACIFIC project, proving that our method is robust against cycle-skipping issues and can provide reasonable uncertainty estimations with a limited computational cost.

Modeling induced seismicity in Groningen based on subcritical stressed faults

Geophysical Journal International - Wed, 02/19/2025 - 00:00

SummaryProbabilistic forecasts of earthquakes caused by anthropogenic changes in subsurface stresses require seismicity models that link rupture nucleation to stress states in geological faults. The recently introduced time-dependent stress response (TDSR) model is based on an exponential dependence of the time-to-failure on stress and is a generalization of the well-known rate-and-state (RS) seismicity model. Unlike RS, TDSR can directly incorporate estimates of the initial stress distribution on affected faults in the seismogenic zone. For the case of the Groningen gas field in the Netherlands, we utilize detailed field and borehole studies to estimate the initial stress distribution and rock properties of the reservoir faults. Using these initial conditions, we show that TDSR outperforms the Coulomb failure model, which assumes instantaneous failure, as well as the RS model, which relies on simplified pre-stress assumptions. Furthermore, an instantaneous Coulomb failure model cannot explain the effect of seasonal gas production in Groningen on the timing of induced earthquakes, in contrast to the TDSR model, which shows a good agreement between prediction and observation. Pseudo-prospective tests show that the seismic response to the reduced production since 2014 could have been predicted as early as 2010 if the production scenario had been known.

Kahramanmaraş earthquake study showcases potential slip rate errors

Phys.org: Earth science - Tue, 02/18/2025 - 20:34

Accurate assessment of the land surface damage (such as small-scale fracturing and inelastic deformation) from two major earthquakes in 2023 can help scientists assess future earthquake hazards and therefore minimize risk to people and infrastructure. However, attaining precise extensive measurements in earthquake zones remains challenging.

Deep-sea organisms shape ocean floor at 7.5 km depth

Phys.org: Earth science - Tue, 02/18/2025 - 20:14

Traces of organisms detected in sediments from 7.5 kilometers below the ocean surface reveal how organisms living in the deep sea are engineering their own environments. Analyses of sediment cores from the Pacific Ocean's Japan Trench, presented in Nature Communications, uncover evidence of burrowing and feeding activity of these deep-sea dwellers.

Understanding long-term development of earthquake-related faults in central Italy

Phys.org: Earth science - Tue, 02/18/2025 - 19:22

Literal groundbreaking research by Dr. Giorgio Arriga enhances our understanding of the long-term evolution of seismogenic (earthquake-related) faults in the Apennines of Central Italy. Arriga's study examines the development of fault systems over millions of years and their impact on present-day seismic hazards. His research included an investigation of faults in the L'Aquila Basin, a region severely affected by a major earthquake in 2009 that claimed over 300 lives, leading to a significant discovery.