Surface displacement data from earthquakes are essential for characterizing the fault slip distribution with depth. The Hebgen Lake earthquake was a large normal event with a geometrically complex surface rupture, which broke across mountainous terrain. This study takes advantage of high-resolution historical stereo-imagery to measure the vertical and horizontal displacement from correlation of the orthorectified pre- and post-earthquake image mosaics. The results reveal new strike-slip surface ruptures which are possibly associated with the aftershocks from 18\textsuperscript{th} August 1959. The kinematic role of these structures is likely related to the accommodation of internal deformation induced by the mainshock strain field. Additionally, the comparison of our results with the existing displacement data shows that the OIC-derived offsets often exceed the field measurements by $>$50\%. We attribute this difference to the inelastic damage accommodated off the main rupture.

Surface melt produces more mass loss than any other process on the Greenland Ice Sheet. In some regions of Greenland with high summer surface melt and high winter snow accumulation, the warm porous firn of the percolation zone can retain liquid meltwater through the winter. These regions of water-saturated firn, which may persist for longer than one year, are known as firn aquifers, commonly referred to as perennial firn aquifers. Here, we use airborne ice-penetrating radar data from the Center for Remote Sensing of Ice Sheets (CReSIS) to document the extent of four firn aquifers in the Helheim, Ikertivaq, and Køge Bugt glacier basins with more than six repeat radar flight lines from 1993 to 2018. All four firn aquifers first appear and/or show decadal-scale inland expansion during this time period. Through an idealized energy-balance calculation utilizing reanalysis data from Modèle Atmosphérique Régionale (MAR) regional climate model, we find that these aquifer expansions are driven by decreasing cold content in the firn since the late 1990s and recently increasing high-melt years, which has reduced the firn’s ability for refreezing local meltwater. High-melt years are projected to increase on the Greenland Ice Sheet and may contribute to the continued inland expansion of firn aquifers, impacting the ice sheet’s surface mass balance and hydrological controls on ice dynamics.

A recognized deficiency of ocean models with a constant-depth vertical coordinate is for truncation errors in the advection scheme to result in spurious numerical mixing of tracers, which can be substantial larger than that prescribed by the model’s mixing scheme. The z~ vertical coordinate allows vertical levels to displace in a lagrangian fashion on time scales shorter than a few days, but reverts to fixed levels on longer timescales, and is intended to reduce numerical mixing from transient vertical motions such as internal waves and tides. An assessment of z~ in a ¼° global implementation of the NEMO model is presented. It is shown that, in the presence of near-inertial gravity waves in the North Atlantic, z~ significantly reduces eulerian vertical velocities with respect to those in a control simulation with the default z* vertical coordinate; that the vertical coordinate approaches an isopycnal, or adiabatic, surface on short timescales; and that both tendences are enhanced when the z~ timescale parameters are lengthened with respect to the default settings. Evaluation of an effective diapycnal diffusivity, based on density transformation rates, shows that numerical mixing is consistently reduced as the z~ timescales are lengthened. The realism of the model simulation with different timescale parameters is assessed in the global domain, and it is shown that drifts in temperature and salinity, and the spindown in z*of the Antarctic Circumpolar Current, are reduced with z~, without incurring significant penalties in other metrics such as the strength of the overturning circulation or sea ice cover.

The SAMI3/ESF (Sami3 is also a model of the ionosphere/equatorial spread $F$) code is used to simulate the growth of equatorial plasma bubbles in the presence of a background wind field based on measured winds. The measured winds exhibit the well-known ‘midnight temperature maximum’ (MTM) pattern, in which an equatorward wind occurs simultaneously with a cessation in the zonal wind. The MTM is often preceded by strong equatorward winds (about 100 m/s). The circumstance where the MTM winds are symmetric across the equator is considered; here the meridional wind component in the southern hemisphere is the reverse of the northern meridional wind. The timing of the wind pattern relative to the imposition of a seed for the ESF instability is explored. We find that the simultaneous occurrence of a seed wave and a strong converging meridional wind pattern can produce post-midnight ESF. We further find that the seed wave and the sudden cessation of the zonal winds can also produce post-midnight ESF. The MENTAT (Magnetic mEridional NeuTrAl Thermospheric) code verifies the occurrence of converging meridional wind patterns such as those simulated here, based on ionosonde data. Results suggest that regional-scale wind measurements would aid in the prediction signal-disrupting ionospheric bubbles.

To understand the overall features of the history of magmatic activities and surface environment on Mars, I used a numerical model of magmatism in the convecting mantle that is nominally anhydrous and internally heated. Magmatism occurs as an upward permeable flow of basaltic magma generated by decompression melting through matrix. The modeled mantle evolves in four stages. In Stage I, high initial temperature in the uppermost mantle causes an extensive magmatism intensified by two types of positive feedback that operate between magmatism and mantle upwelling flow, the MMUb and MMUc feedback: the buoyancy and volume change of matrix, respectively, caused by migrating magma that a mantle upwelling flow generates intensify the flow itself to generate more magma. The stratification suppresses mantle convection and magmatism for the next tens to hundreds of millions of years, allowing heat to build up in the mantle by internal heating (Stage II). Eventually, magma is generated at depth, and the MMUb feedback operates to cause an episodic plume magmatism that releases water from the interior of Mars (Stage III). The plume magmatism also stirs the mantle to make it more homogeneous and extracts heat producing elements from the deep mantle to let the magmatism itself wane and cease. In the final stage IV, mantle convection becomes more like a thermal convection. The episodic magmatism and water outgassing in Stage III account for the magmatism and clement surface environment observed for early Mars.

This material is based upon work supported by DOE E3SM (DE-SC0019278), NASA (OSTFL 80NSSC22K1743), and NSF (OAC-2004993). Work performed at UC Irvine, located on the ancestral, unceded homelands of the Acjachemen and Tongva peoples.

A document by Sydney JN Baratta. Click on the document to view its contents.

Key Points 1. Regional propensity of flood tail behavior is shown across a diverse geographical range based on the analysis of common streamflow dynamics. 2. Temporal variability in catchment storage, driven by high evapotranspiration and dry soils, is a key mechanism for heavy-tailed floods. 3. Examining flood generation processes aids in unraveling the connections between flood tail behavior and seasons or catchment sizes.

The simulated quasi-biennial oscillation (QBO) in the Energy Exascale Earth System Model version 2 (E3SMv2) is characterized by a shorter period and stronger amplitude compared with its predecessor E3SMv1. This is primarily attributed to updates to the deep convection parameterization which makes convection more intense but less frequent while leaving the time-mean convective heating tendency almost unchanged. Amplitudes of momentum fluxes associated with parameterized gravity waves, which are determined by the square of convective heating tendency, are consequently intensified. In addition, stronger planetary waves, another contributor to the QBO driving, are simulated in E3SMv2 in part due to tropospheric processes. Furthermore, there is evidence that planetary wave generation is present in the stratosphere due to dissipation of amplified parameterized gravity waves. These factors are found to be responsible for the stronger and faster QBO simulated in E3SMv2.

Spectra of small-scale sprite structures, downward and upward propagating streamers, glow, and beads, were recorded with a slit-less spectrograph at 10,000 frames per second (fps) from aircraft missions in 2009 and 2013. The spectra are dominated by emissions from molecular nitrogen, the 1 positive band in the red, and in the blue the 2 positive band plus the 1 negative band of molecular nitrogen ions. The excitation threshold for the blue emissions is higher than for the red emissions so the blue/red ratio can, in principle, be used as a proxy for the electron energy leading to the emissions. We extracted for analysis time series of spectra from 11 sprites: 18 time series from downwards propagating streamers, 6 from upward propagating streamers, 14 from glow and 12 from beads. The total number of spectra in the 50 time series is 953. Blue emissions are almost exclusively associated with streamers indicating the more energetic nature of streamers compared with glow and beads. Both downward and upward propagating streamers start and end with low blue emissions indicating time variations in the associated processes. Because the red and blue nitrogen emissions are significantly affected by quenching, which is altitude dependent, and we do not have sufficiently accurate altitudes, the observed spectral blue/red ratios cannot be directly applied to sprite models.

Beginning in 1964, an academic lineage of Robert DuBois and his students, Daniel Wolfman and Jeffrey Eighmy, developed dedicated United States-based archaeomagnetic research programs. Collectively, they analyzed over 5377 archaeomagnetic sites, primarily from North America, dated to less than 2000 years old. Yet despite their decades of effort, few journal publications resulted. Most of their published results are embedded in archaeological reports, often without technical data, which limits the data’s accessibility. Furthermore, when published, the results are generally averaged at the site-level using statistical conventions different from today’s standards, limiting the data’s comparability and (re)usability. In 2015, we undertook a salvage archival study to digitize the surviving data and metadata from the scientists’ individual estates and emeritus collections. We digitized measurement data from more than 51,000 specimens, reinterpreted them using modern conventions, and uploaded them to the FAIR-adhering magnetic data repository – MagIC. The reinterpreted site-level results from the three laboratories are mutually consistent, permitting the individual datasets to be combined and analyzed as single regional entities. Through incorporation into the MagIC repository, these legacy data are now accessible for incorporation into archaeomagnetic and global magnetic field modeling efforts, critical to understanding Earth’s magnetic field variation through time. In the Four Corners region of the United States Southwest, this digitized archive advances the development of a new regional paleosecular variation curve used in archaeomagnetic dating. This project highlights both the value and complexities of managing legacy data; the many lessons learned set a precedent for future paleomagnetic data recovery efforts.

We evaluate for the first time the large-scale influence of the upstream interplanetary magnetic field (IMF) magnitude and orientation on Martian proton aurora. We identify a correlation between proton aurora activity and IMF magnitude that varies seasonally, with highest correlations around Mars southern summer solstice when proton aurora activity reaches an annual high. We identify preferentially increased proton aurora emission enhancements at IMF cone and clock angles consistent with the shape of the Parker spiral at Mars’s heliocentric distance. An increased proton aurora occurrence rate is observed for near-radial IMF orientations, particularly evident when the hydrogen corona and bow shock are annually decreased. Lastly, our results suggest that dayside magnetic reconnection may influence proton aurora, which are observed to have preferentially higher occurrence under strong ±Bz orientations. These findings enhance our understanding of the upstream IMF’s influence on Martian proton aurora as an important driver for auroral brightness and occurrence.

In 2020, the long-persisting Meiyu season around the Yangtze River (YR) started in early-June and ended in mid­–late-July. Its accumulated precipitation amount broke the record since 1961. We showed that the sequential warm and cold Meiyu front regulated by the North Atlantic Oscillation was responsible for this record-breaking Meiyu rainfall. From 11 to 25 June with the positive NAO, the interaction between South Asian High (SAH) and western Pacific subtropical high maintained a warm front to strengthen the rainband north of YR. Afterward, the coupling between SAH and mid-latitude Mongolian Cyclone induced a cold front, which retreated the rainband to the south of YR from 30 June to 13 July with the negative NAO. Although the ECMWF S2S successfully predicted the warm-front-related Meiyu rainband, it failed to forecast the Meiyu rainband in the cold-front period, suggesting a great challenge of the S2S forecast on Meiyu rainfall.

A document by Alexander Lipatov. Click on the document to view its contents.

Accurate earthquake location and magnitude estimation play critical roles in seismology. Recent deep learning frameworks have produced encouraging results on various seismological tasks (e.g., earthquake detection, phase picking, seismic classification, and earthquake early warning). Most existing machine learning earthquake location methods utilize waveform information from a single station. However, multiple stations contain more complete information for earthquake source characterization. Inspired by recent successes in applying graph neural networks in graph-structured data, we develop a Spatio-Temporal Graph Convolutional Neural Network (STGCN) for estimating earthquake locations and magnitudes. Our graph neural network leverages geographical and waveform information from multiple stations to construct graphs automatically and dynamically by an adaptive feature integration process. Given input waveforms collected from multiple stations, the neural network constructs different graphs and fuses spatial-temporal consistency effectively from various stations based on graphs’ edges. Using a recent graph neural network and a fully convolutional neural network as baselines, we apply STGCN to earthquakes cataloged by Southern California Seismic Network from 2000 to 2019 and induced earthquakes collected in Oklahoma from 2014 to 2015. STGCN yields more accurate earthquake locations than those obtained by the baseline models and performs comparably in terms of depth and magnitude prediction, though the ability to predict depth and magnitude remains weak for all tested models. Our work demonstrates the potential of using graph neural networks and multiple stations for better automatic estimation of earthquake epicenters.

The motion of the Adriatic microplate is thought to be highly sensitive to the surrounding subduction zones and the convergence of Africa and Eurasia. However, our understanding of the mantle dynamics in the Mediterranean region and its effect on plate motion remains incomplete. Here, we present a large set of 3D thermomechanical models of the entire Mediterranean region over the last 35 Myr to understand what controls the motion of the Adriatic microplate. The simulations take the convergence of the African and Arabian plates with the Eurasian plate into account, along with the dynamics of the subduction systems in the western (Apennines-Calabria), central (Dinarides-Hellenides) Mediterranean and in the Alpine-Carpathian region. Our results demonstrate that the subduction systems around Adria are highly coupled, which gives rise to complex asthenospheric flow in the central Mediterranean. We find that the plate motion of the Adriatic microplate over the last 35 Myr is controlled by interplay of three main factors: 1) the convergence between the African and Eurasian plates, 2) the retreat of the Alpine subduction zone to the north of Adria, and 3) the distance between the Calabrian and Hellenic subduction zones around Adria. Furthermore, in a system characterized by active convergence between Africa and Eurasia, the slab pull exerted by nearby subduction zones can only notably influence the motion of the Adriatic microplate if these subduction zones are located within a few hundred kilometers of Adria.

Stress drops for injection-induced earthquakes near the Dallas-Fort Worth International Airport in the Fort Worth Basin (FWB), Texas are estimated. The mean stress drop for the Airport sequence is lower than other FWB earthquake sequences. Airport earthquake stress drops increase with radial distance from the injection point, but only over the first 1.5 km; estimates for more distant earthquakes are spatially independent, consistent with other FWB sequences. The low stress drop Airport events occurred shortly after the initiation of injection on a fault extremely close to the well, and we suggest that here we uniquely captured the initial low stress drops predicted by direct triggering of earthquake via rapid pore pressure changes.

Glacigenic bedforms such as multiple glacial lineations and moraines on the Chukchi and East Siberian margins reveal recurrent waxing and waning by voluminous ice masses. Despite their paleoclimatic significance, the timing, geographic distribution, and mechanisms of these glaciations remain inadequately understood. To enhance our understanding of the Quaternary Arctic glacial history, we study high-resolution swath bathymetry and subbottom profiling data with lithostratigraphy and provenance of four sediment cores. These data characterize deposits of the last two glaciations at the Chukchi margin and adjacent basins. In all cores, multiple peaks of plagioclase are prominent in both glacial intervals, probably reflecting predominant glacigenic input from the East Siberian Ice Sheet (ESIS). Peaks of dolomite and quartz for tracing the Laurentide Ice Sheet sources occur around the last glacial/deglacial interval and in sediment preceding the penultimate glaciation. By integrating seismostratigraphy with sediment cores, we constrain the formation of mid-slope moraines on the western side of the Chukchi Rise to the penultimate glaciation (estimated age range MIS 4 to 6). Considering the coeval glacial erosion off the East Siberian margin, our results confirm that the ESIS at that time extended to water depths of ~650/950 m on the Chukchi Rise/East Siberian margin. In comparison, the last ESIS (MIS 2 to possibly 4) was smaller, with the identified seafloor imprint limited to water depths of ~450 m on the Chukchi Borderland, while its extent on the East Siberian margin remains to be determined.