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Simultaneous Estimation of Slip Distribution and Correlation Length Using Bayesian Optimisation and the Impact of Inhomogeneous Observation Network Distribution

Geophysical Journal International - Mon, 12/22/2025 - 00:00

SummaryThis study develops a Bayesian optimisation method of coseismic slip distributions and the correlation lengths of the von Kármán autocorrelation function, which can realize more reliable regularisation grounded in geophysical analysis (VKR). To validate VKR and its dependence on the observation, synthetic tests using data from inhomogeneously distributed Global Navigation Satellite System (GNSS) stations and Synthetic Aperture Radar (SAR) were conducted. When observation stations surround the source fault, the assumed slip distribution and the correlation length were well recovered with some artificially extended slip due to the inhomogeneity of the observation network. Moreover, when observation stations exist only on one side of the fault, the method recovered the slip and other parameters with accuracy comparable to that of the surrounding-case scenario, albeit with slightly increased uncertainty of the parameters. This highlights the importance of uncertainty evaluation for slip and correlation length parameters, especially under biased observation networks. Applying existing Laplacian smoothing methods to the same experiments produced models globally consistent with VKR, demonstrating that the proposed method, despite additional non-linear parameters, achieves comparable estimation accuracy. Existing method showed isotropic correlations of slip variables, whereas VKR exhibited correlations elongated along the strike direction, reflecting its ability to independently regularise along strike and dip via correlation length parameters. These correlation patterns were most pronounced in deeper fault regions, where regularisation dominated over observational constraints. Cluster analysis of the Markov samples revealed that VKR captured a more diverse set of slip distribution models, with cluster differences most evident in deeper fault regions. These analyses underscore the importance of regularisation choice and its impact when evaluating and interpreting slip distributions. We also applied VKR to the actual data of the 2024 Noto Peninsula earthquake in Japan, observed by dense GNSS networks and SAR. The estimated slip distribution featured multiple slip areas in the eastern and western peninsula, consistent with previous studies and Laplacian smoothing-based results. The correspondence between estimated slip distribution and correlation length was confirmed, although it did not match previous empirical findings. To further examine the effect of observation network configuration, we performed additional inversions using a reduced set of actual data. The resulting slip distribution was smoother, and the estimated correlation lengths were larger and more uncertain. Our results reconfirm that simultaneous estimation of slip distribution and correlation length produces mutually consistent values, both of which depend on the spatial distribution of observation points. The results also demonstrate the strong dependence of estimated slip distribution and correlation lengths on the observation network. Therefore, future studies of coseismic slip self-similarity, using observed data, should incorporate parameter analyses that account for network resolution effects.

Extraction and performance analysis of tidal signals from non-stationary continuous gravity data based on TVF-EMD

Geophysical Journal International - Mon, 12/22/2025 - 00:00

SummaryThe precise extraction of tidal signals from non-stationary gravity observations is a central challenge in geophysics, where accuracy is often limited by mode mixing in data preprocessing algorithms. This study evaluates the performance of the Time-Varying Filter-based Empirical Mode Decomposition (TVF-EMD) method to address this issue. We employed a progressive validation pipeline: the method was first verified on simulated signals, then rigorously tested against a high-fidelity benchmark from a superconducting gravimeter (SG), and finally applied to one month of continuous data from an Atom Gravimeter (AG) at the Yilan station. Results demonstrate that TVF-EMD dramatically suppresses mode mixing, with the energy of transient spikes in its residual being an order of magnitude lower than that from the conventional Ensemble Empirical Mode Decomposition (EEMD) method. The tidal signal reconstructed by TVF-EMD achieved the highest cross-correlation coefficient and the smallest root mean square error when compared to the theoretical gravity tide. Subsequent harmonic analysis confirmed that TVF-EMD yielded the lowest errors across all major tidal constituents. These findings validate TVF-EMD as a superior preprocessing framework for tidal analysis, particularly for enhancing the reliability of geophysical parameter inversion from short-duration records obtained with next-generation quantum sensors.

Triple-Difference Surface-wave Travel Time Adjoint Tomography

Geophysical Journal International - Mon, 12/22/2025 - 00:00

SummaryStructural boundaries are often the features of most interest geologically, but imaging them can be difficult due to wavefield scattering and interference caused by the sharp velocity contrasts. One example of this is the apparent Rayleigh-wave anisotropy (1-psi anisotropy) that has been observed near major structural boundaries using seismic arrays. The cause of the apparent anisotropy is the interference between the incident surface wave and waves scattered from velocity discontinuities. In this study, we first investigate the sensitivity of apparent anisotropy measurements to lateral boundary sharpness through 2D full waveform simulations. We demonstrate that 1-psi anisotropy can vary based on boundary sharpness, station spacing, and period of surface waves. We show that a misfit defined using triple-difference travel times, i.e. the difference in double-difference travel times between station pairs with opposite propagation directions, well characterizes the apparent anisotropy. The sensitivity kernel for this triple-difference misfit can be constructed using the adjoint method. We show that triple-difference travel times are mainly sensitive to velocity contrasts rather than absolute velocities, in contrast to double-difference travel times. With sensitivity kernels constructed, we demonstrate how triple-difference travel times can be combined with double-difference travel times into a tomography inversion. We show that by including triple-difference travel times, seismic inversions converge faster and resolve boundary and average structure better in early iterations, compared to using double-difference travel times alone. Recent advancements in dense array experiments could facilitate the application of this method to better delineate tectonic and basin structural boundaries.

Уникальность спина 1/2

Успехи физических наук - Sun, 12/21/2025 - 21:00

С.В. Петров

Статья посвящена 100-летнему юбилею квантовой механики и, в частности, спину электрона — феномену, не имеющему аналога в классической физике. Гипотеза спина электрона была выдвинута Уленбеком и Гаудсмитом в 1925—1926 гг. для объяснения многочисленных экспериментальных данных. Спустя два года наличие спина электрона было обнаружено Дираком при построении релятивистского волнового уравнения для свободной частицы. Для Дирака это оказалось большим сюрпризом, поскольку, как он утверждал позднее (в 1977 г.), его целью было получить релятивистское волновое уравнение для простейшей частицы, каковой он считал частицу с нулевым спином. А оказалось, что простейшей является частица со спином 1/2.

60 лет Институту теоретической физики им. Л.Д. Ландау Российской академии наук

Успехи физических наук - Sun, 12/21/2025 - 21:00

Muddy eruption at Yellowstone's Black Diamond Pool captured on video

Phys.org: Earth science - Sun, 12/21/2025 - 19:21

"Kablooey!" That's the word U.S. Geological Survey volcanic experts used to describe a muddy eruption at Black Diamond Pool in Yellowstone National Park on Saturday morning.