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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.

Flight Demonstration of a CubeSat Sporadic-E Detector

Recent articles in Advances in Space Research - Sun, 12/21/2025 - 19:11

Publication date: Available online 13 December 2025

Source: Advances in Space Research

Author(s): Bruce A. Fritz, Kenneth F. Dymond, Ellen J. Wagner, Andrew C. Nicholas, Scott A. Budzien, Andrew W. Stephan