Abstract We investigate co‐ and post‐seismic P ‐wave velocity ( V p ) changes following the July 2019 Mw 7.1 Ridgecrest strike‐slip earthquake using time‐lapse tomography from 50,345 P ‐wave arrivals (2011–2024). Co‐seismically, V p changes correspond to the volumetric strain change lobes of the earthquake, increasing in compressional zones and decreasing in tensional zones. Post‐seismically, V p changes exhibit a reverse pattern, suggesting ongoing subsurface recovery. Notably, the Coso volcanic field, although distal to the rupture, shows significant co‐seismic velocity reduction and rapid post‐seismic recovery, likely indicating fluid migration or poroelastic effects. These results reveal the complex mechanical and hydrological responses to co‐seismic stress changes and provide important insights into post‐seismic healing processes. Our findings offer robust seismic evidence for the response of material properties to crustal deformation, contributing to improved understanding of structure changes in the earthquake process.
Abstract To understand what governs earthquake size, we investigated the 2021 Mw 7.0 Japan Trench earthquake, which began near a nest of repeating earthquakes. High‐precision hypocenter relocation and P‐waveform correlation show that the mainshock initiated nearly identically to Mw 3.8 repeaters. Waveform deconvolution reveals that, after breaking the Mw 3.8 patch within 0.1 s, the mainshock rupture cascaded through Mw 5–6 patches within 2 s and into the main slip area at 3–6 s. Four preceding Mw 5.1–6.1 events, some with higher initial moment rates, did not rupture this main area, likely because the locked region remained too far from failure. Their repeated occurrence may reflect progressive unlocking of this region. In 2021, a start nearly identical to Mw 3.8 repeaters cascaded hierarchically into an Mw 7.0 rupture, suggesting that earthquake size depends less on how rupture begins than on whether surrounding locked regions are ready to fail.
Abstract Variations in melt supply can shift slow and ultraslow ridges between magmatic and tectonic accretion modes, but whether this effect persists at Earth's slowest‐spreading ridge remains unclear. The eastern Gakkel Ridge provides a critical test because it spreads at only ∼6–10 mm/yr yet shows anomalously strong magmatism. We reconstruct sediment thickness and residual basement across the Eurasian Basin using seismic constraints and time‐dependent sedimentation models for the poorly constrained eastern Nansen Basin. Most of the western Eurasian Basin shows deep residual basement and variable flank asymmetry, consistent with magma‐poor ultraslow accretion. Eastward, residual basement becomes progressively shallower and more symmetric. In the eastern Nansen Basin, shallow residual basement persists even under maximum sedimentation, indicating sustained crustal thickening on both conjugate flanks since ∼45 Ma. These results show that enhanced melt supply can shift oceanic crustal accretion toward a near‐symmetric, magma‐dominated mode even at Earth's slowest‐spreading ridge.
Abstract Under a warming climate, the magnitude and frequency of intense precipitation are expected to increase globally, on average. However, changes in the regional variability of short‐duration high‐intensity (SDHI) precipitation across the contiguous United States—both temporally and spatially—remain uncertain, and most projections rest on resolutions too coarse to resolve the responsible processes. Herein, convection‐permitting, dynamically downscaled simulation output at 3.75 km grid spacing and 15‐min intervals is used to examine potential changes in the occurrence, accumulation, and magnitude of sub‐daily precipitation relative to simulated historical levels. Changes are concentrated at both tails of the intensity distribution: precipitation at or above the percentile increases significantly in five of seven regions, exceeding 100% in the Northwest, while lighter intensities decrease by 10%–40%. These changes are regionally and seasonally concentrated rather than uniform, and their dependence on accumulation duration varies by region, so future hydroclimates may be characterized by fewer light‐to‐moderate events punctuated by more intense ones, a redistribution that will challenge water management and infrastructure design.
Abstract Gamma‐ray glows are prolonged enhancements of gamma rays from thunderclouds, which are often linked to large‐scale electric fields rather than individual lightning. The link between glows and lightning remains poorly understood. Here, we analyzed 300 glows observed during the ALOFT aircraft campaign and optical lightning detected by GLM. The results indicate that lightning becomes progressively less likely to coexist with a glow as the gamma‐ray intensity increases. Lightning activity also decreases several seconds before the glow peak but increases sharply afterward. Furthermore, approximately 78% of glows are followed by lightning within 1 s and 10 km, and the lightning frequency during the following second is 5.3 times that during the preceding second. These results reveal that lightning is closely related to glow reduction, suggesting that glow‐producing high‐field conditions and lightning discharge are closely coupled in the evolution of the thunderstorm electrical environment.
