Abstract Investigating the geologic record of near‐trench coseismic strain release is critical for estimating the slip distribution and tsunamigenic potential of future large subduction zone earthquakes. However, the style and extent of upper plate coseismic deformation offshore in subduction zones is poorly constrained. To address this knowledge gap, we integrate shipborne multichannel seismic and multibeam data with targeted autonomous underwater vehicle (AUV) bathymetry and chirp data to resolve the updip limit and mode of coseismic slip along the frontal thrust fault zone in central and southern Cascadia. Detailed fault mapping and characterization reveals four distinct styles of Holocene deformation along the frontal thrust fault zone, including fault propagation folding, imbricate thrusting, breakthrough thrusting, and frontal erosion through widespread mass wasting. Joint interpretation with crustal‐scale seismic data shows that these variations in near‐surface deformation style are clearly linked to changes in megathrust geometry and accretionary mode at depth. Additionally, AUV data provide abundant on‐fault geologic evidence for discrete and episodic near‐surface deformation, including primary fault and fold scarps, bending moment fault scarps, punctuated growth strata, and discrete single event fault offset, that we consider to be predominantly coseismic. The widespread distribution of Holocene active, likely coseismic, frontal thrust deformation presented in this study highlights the potential for variable mode coseismic slip to the trench in Cascadia. These results provide an unprecedented view into the shallow megathrust structure and heterogeneity in Cascadia that is critical for estimating earthquake and tsunami hazard impacts locally and for understanding shallow megathrust slip behavior globally.
Abstract For nearly 50 years, the origin of the candidate seismic signals recorded by Viking 2 remained unresolved because of limited instrumental sensitivity, onboard observation, data compression, and the absence of Martian seismic context. Here we reconstruct the Viking seismic workflow and reinterpret the two Viking candidate events, recorded on sol 53 and sol 80, using the seismic context established by InSight. We show that the Viking seismometer was optimized for high‐spectral‐frequency seismic signals, consequently reducing its sensitivity to low‐spectral‐frequency events. If the original 10‐s S‐P travel‐time difference is correct, the inferred location of the sol 80 event overlaps the broad northern‐plains source region suggested for the seasonally recurrent high‐spectral‐frequency and 2.4‐Hz marsquake populations observed by InSight. Alternatively, if the first‐arrival phase represents a crustal conversion phase rather than a direct P wave, the sol 80 event corresponds to a distant tectonic (low‐spectral‐frequency or broadband) marsquake with an estimated moment magnitude of MW 4.6–4.8 or MW 4.9–5.1. A meteorite impact origin cannot be excluded either. The two Viking seismic signals decay more rapidly than typical InSight marsquakes, suggesting heterogeneity in the Martian attenuation structure. Together, these findings integrate Viking observations into the modern framework of Martian seismicity, illustrating how a legacy planetary data set can acquire renewed scientific implications when re‐examined in light of subsequent mission data.
Knowledge of crater degradation rates on the Moon is fundamental for dating individual craters, understanding material transport, and investigating crater equilibrium, with broader implications for water ice exploration, regolith evolution, and impact flux reconstruction. However, direct observational constraints on the degradation rates of hundred-meter-scale lunar craters remain scarce, and regional variations between mare and highland terrains are poorly quantified. Here, we measure the diameters and depths of 56,229 small impact craters across the Apollo, Luna, and Chang'E landing regions using high-resolution optical and topographic data. We then systematically simulate the production and evolution of crater populations from geological unit emplacement to the present, accounting for both diffusive degradation and catastrophic obliteration. By comparing observations with forward simulations, we provide the most extensive observational constraints to date on the degradation rates and lifetimes of small craters with diameters of 50-500 m. At these scales, the estimated topographic diffusivities increase from 0.62 to 2.33 m(2) /Myr in the maria and from 2.27 to 4.54 m(2)/Myr in the highlands. Regional variations in degradation rates are most strongly associated with meter-scale slope rather than adopted proxies for target properties. The inferred lifetimes imply that subhectometer micro cold traps are short-lived (<100 Myr) and thus host only recently delivered water ice, whereas larger cold traps of several hundred meters can persist over geological timescales and are favorable for water ice accumulation. Our results further indicate that crater equilibrium at small diameters is achieved mainly through diffusive degradation rather than superposition, and that equilibrium crater abundance is expected to vary across the Moon.
Abstract Accurate short‐term tropical cyclone (TC) intensity forecasting remains challenging because rapidly evolving inner‐core structures are difficult to observe at sufficiently high temporal resolution. Here, we derive an area‐mean upper‐level vorticity indicator (VORm) from minute‐scale atmospheric motion vectors retrieved from the Fengyun‐4B Geostationary High‐speed Imager (FY‐4B/GHI) using the Single‐Plane Assumption–Fast Approximate Barnes Interpolation framework. Analysis of western North Pacific TCs shows that VORm closely follows the broad evolution of storm intensity while retaining substantial high‐frequency structural variability. VORm exhibits a strong contemporaneous association with TC intensity and retains information related to subsequent 6‐hr intensity change after accounting for the current intensity and preceding intensity tendency, indicating potential value for short‐term intensity prediction. Forecast experiments further demonstrate this predictive potential. In the linear framework, incorporating VORm reduced the pooled 6‐hr RMSE from 6.27 to 5.97 kt, indicating additional predictive information beyond conventional intensity and environmental predictors. In the nonlinear XGBoost framework, VORm further reduced the RMSE from 6.26 to 6.18 kt even when the preceding 6‐hr intensity tendency was explicitly included, indicating that VORm still provides additional predictive information beyond recent intensity evolution. Because FY‐4B/GHI winds and the derived vorticity can be obtained with very low latency, this approach offers a practical pathway for rapidly incorporating high‐frequency inner‐core structural information into short‐range TC intensity forecasting.
Abstract Ionospheric scintillation disrupts trans‐ionospheric radio signals and represents significant challenges for critical communication and navigation systems. Here we document that hot flow anomalies (HFAs), transient disturbances formed near Earth's bow shock, can contribute to scintillation near the cusp. We used coordinated multi‐instrument observations including GNSS receivers, SuperDARN, AMPERE, DMSP/SSUSI, MMS to link an upstream HFA to the scintillation in the polar ionosphere. During 10:47–10:57 UT on 19 November 2015, enhanced phase scintillation was observed, along with a convection vortex, enhanced field‐aligned currents (FACs) and nearby particle precipitation. An HFA and associated high‐speed jets (HSJs) were observed in the corresponding magnetic local time (MLT) region of the magnetosheath. Our analysis indicates that the HFA disturbs the magnetopause and enhances the FACs, causing the localized ionospheric density gradient instability, thereby triggering the ionospheric scintillation. These results show that the particle precipitation caused by HFAs can strongly affect the cusp plasma and trigger significant phase scintillation. Our results provided direct observational evidence that HFAs are a contributing source of polar space‐weather impacts on GNSS and radio systems.
