A document by Sebastian Uhlemann. Click on the document to view its contents.

A document by Filipi Vianna. Click on the document to view its contents.

Radio-echo sounding (RES) has shown that large-scale folds in the englacial stratigraphy is ubiquitous in Greenland’s ice sheet. However, there is no consensus yet on how these folds form. Here, we use the full-Stokes code Underworld2 to simulate ice movements in three-dimensional convergent flow, mainly investigating the effect of ice anisotropy due to a crystallographic preferred orientation, vertical viscosity and density contrasts in ice layers, and bedrock topography. Our simulated folds show complex patterns and are classified into three types: large-scale folds, small-scale folds and basal-shear folds. The amplitudes of large-scale folds tend to be at their maximum in middle ice layers and decrease towards the surface, in accordance with observations in RES data. We conclude that bedrock topography contributes to perturbations in ice layers, and that ice anisotropy amplifies these into large-scale folds, while vertical viscosity contrasts in ice layers are insufficient for large-scale fold amplification.

In the past two decades, the central portion of Campi Flegrei caldera has experienced ground uplift of up to 15 mm/month, and a consequent increase in the rate, magnitudes and extent of seismicity, especially in the past two years. We use a new method for multi-scale precise earthquake location to relocate the 2014-2023 seismicity and map in detail currently activated fault zones. We relate the geometry, extent, and depth of these zones with available structural reconstructions of the caldera. The current seismicity is mainly driven by the time-varying, ground-uplift induced stress concentration on pre-existing, weaker fault zones, not only related to the inner caldera, dome resurgence but also to ancient volcano-tectonic collapses and magma emplacement processes. The extent of imaged fault segments suggests they can accommodate ruptures up to magnitude 5.0, significantly increasing estimates of seismic hazard in the area.

Many Earth system models (ESMs) approximate surface emissivity as a constant. This broadband approximation reduces computational burden, yet biases longwave (LW) atmospheric fluxes and heating by neglecting the spectral structure of surface emissivity and atmospheric absorption. These biases are largest over surfaces with strongly varying emissivity and minimal atmospheric opacity (e.g., due to water vapor and clouds). Our study focuses on liquid water, ice, and snow surfaces. We use LW spectral emissivity ε(λ) calculated via the Fresnel equations and validated against a dataset of spectral surface emissivity. We flux-weight and bin ε(λ) into 16 spectral bands accepted by an offline single-column atmospheric radiative transfer model (RRTMG_LW) commonly used in ESMs (including E3SM and CESM). We quantify flux and heating biases introduced by broadband emissivity assumptions in comparison with the 16-band spectrally resolved case for three different surface types, three standard atmospheric profiles, and for the key drivers surface temperature, cloud water path, and atmospheric water vapor. In addition, we devise and test novel greybody and semi-spectral methods of representing ε(λ) with the goal of reducing biases while preserving computational efficiency. We find that typical broadband assumptions artificially cool Earth’s surface, thereby stabilizing the lower troposphere. LW upwelling flux is overestimated by 4.5 W/m2 (~1.4%) at the bottom of a mid-latitude winter atmosphere over an ice surface, and by 3.3 W/m2 (~1.4%) at the top of atmosphere. Lastly, we find that a semi-spectral approach (five bands instead of 16) reduces biases by up to 99% relative to the broadband approximation.

Ionospheric plasma blobs have long been studied since it was first reported in 1986. Blobs are localized regions of enhanced plasma with a factor of 2 or 3 above ambient plasma. In this paper, we studied the occurrence of blobs over Nigeria (9.08⁰N, 8.67⁰E geographic coordinates) using the SWARM constellation satellites – ionospheric plasma density dataset specifically. We considered only the nighttime pass of the satellites over Nigeria with time frame 18:00 to 04:59 LT. The satellites passed over Nigeria 126 times in 2019 with 41 cases of plasma blobs. The results show that 58% of the cases were found without bubbles nearby, 29% of the cases were found in the presence of small-scale fluctuations in ionospheric plasma density (henceforth “SSFiI”). From the spectral analysis, the average wavelength, period and the propagating speed of SSFiI are 11 km, 2-4 seconds, and 2.75 – 5.5 km/s, respectively. The rate of change of the electron density inside the blobs associated with SSFiI was ~50% above that of the blobs in the absence of SSFiI. This suggests that bubbles may not be the only prerequisite for the development and dynamics of blobs; and SSFiI may play a significant role in the morphology and dynamics of blobs.

The crustal components in a magma plumbing system often contain mechanically heterogeneous layers and structural discontinuities such as pre-existing fracture (PEF) systems. Such layers and discontinuities, depending upon their mechanical properties, can either facilitate upward magma movement or inhibit it at some depths by acting as stress barriers. This study considers a visco-plastic crustal rheology to study the variation of yield strength around the two lateral tips of an elliptical magma chamber (MC), aided by the presence of a PEF, by employing a finite element modelling (FEM) approach. The orientation of the PEF is varied in the FE models and the patterns of localized tensile stress have been examined from these models. The model results find no difference between the yield strength at the two lateral tips of the MC, when there is no PEF in the crustal domain. On the other hand, the presence of a PEF significantly decreases the yield strength around the associated MC tip. We also observed that the yield strength around the MC is also dependent upon the vertical and horizontal separation between the MC and the PEF. When a heterogeneous layer above the MC is taken into consideration, the yield strength depends on whether the PEF terminates above, within, or below the heterogeneous layer. The model results show that the difference in the magnitude of yield strength between the two MC tips is least when the PEF is located above the heterogeneous layer, whereas, it is maximum when the PEF is located below the MC. These results provide finer interpretation in understanding the kinematic evolution of a magma plumbing system, with large structural discontinuities housed within shallow crustal depths.

A document by Yasuo YABE. Click on the document to view its contents.

A document by Raj Pandya. Click on the document to view its contents.

First part of the paper is devoted to explanation of unusual WSW-ENE position of High Atlas belt. Explanation is given by permanent action of tides, which create folding of this belt and its permanent uplift up to high over 4000 m. Tidal origin of Marrakesh earthquake 2023 is proven by maximum Moon declination 27° 31.

The slab dip and long-term coupling at the plate interface can vary both between and within subduction zones. How these variations affect the long-term subduction dynamics and mantle rheology is important for understanding plate tectonics and its evolution. This paper presents two-dimensional (2D) models that examine the surface plate velocity and dynamic weakening of the asthenosphere as a function of six values of plate interface coupling (3.1x10^20, 1x10^21, 3.1x10^21, 1x10^22, 3.1x10^22, 1.0x10^23 Pa·s) and three values of initial slab dip (30^o, 45^o, 60^o). The models use a composite viscosity in the upper mantle and were run for 2000 time-steps. The instantaneous results show subducting plate speed and dynamic weakening at the lithosphere-asthenosphere boundary (LAB) increase with decreasing inter-plate coupling, and peak for models with an initial dip of 45^o. For time-dependent models, subducting plate speed also increases with decreasing inter-plate coupling. However, models with an initial slab dip of 30^o produce the fastest subducting plate speeds over time. The thickness of the dynamically weakened LAB evolves over the course of subduction. The results indicate the subducting plate velocity is correlated not only with the imposed inter-plate coupling, but also with the dynamic weakening of the LAB region. The weaker the inter-plate coupling, the easier for the slab to descend into the mantle and dynamically weaken the asthenosphere due to the strain-rate dependent rheology. This reduced viscous resistance to slab sinking facilitates subducting plate and mantle flow over time, thus easing the subduction process of plate tectonics.

The interactions between climate, tectonics and surface processes have become a research hotspot in Earth science in recent years. Although various insights have been achieved, the relative importance of climatic and tectonic forcing in influencing the evolution of mountain belts still remains controversial. In order to investigate the tectonic and topographic evolution, as well as the formation mechanism of the eastern Himalayan syntaxis, we developed a comprehensive 2D climatic-geomorphological-thermomechanical numerical model and conducted over 200 experiments to test the influences of convergence rate, average precipitation and initial geothermal gradient on orogenic wedge. The results indicate that, for a specific orogenic wedge, its tectonic and topographic evolution primarily relies on the relative strength of tectonic and climatic forces, rather than their respective magnitudes. A syntaxis is the result of the combined effects of tectonic forces, climatic forces and geothermal field. In mountain belts, once the convergence rate and average precipitation fall within a Type D zone determined by the crustal thermal structure, a sustained, stationary, localized and relatively rapid erosion process will be established on the windward flank of the orogenic wedge. This will further induce sustained and rapid uplift of rocks, exhumation and deformation, ultimately forming a syntaxis. In this context, syntaxis is the inevitable system's outcome under various physical laws, including conservation of mass, momentum and energy, rheology, orographic precipitation, surface processes, etc. Orogens are best viewed as complex open systems controlled by multiple factors, none of which can be considered as the sole cause of the system's outcome.

A significant increase in the number of anthropogenic objects in Earth orbit has necessitated the development of satellite conjunction assessment and collision avoidance capabilities for new spacecraft. Often, the greatest source of uncertainty in predicting a satellite's trajectory in low Earth orbit originates from atmospheric neutral mass density variability caused by enhanced geomagnetic activity and solar EUV absorption. This work investigates the impacts of solar and geomagnetic index forecasting uncertainty on satellite drag and satellite maneuver decision-making. During an averaged point in the solar cycle, accurate index forecasts with reduced uncertainty are shown to provide significantly improved advance notice for dangerous conjunction events above 500 km. Below 500 km, forecast improvements are less impactful. This boundary of utility from forecast improvements shifts upward and downward during solar maximum and solar minimum, respectively. Improved index forecasts are shown to have little impact on making maneuver decisions 12-24 hours from a potential conjunction event, but are demonstrated to be very useful when trying to make maneuver decisions with more lead time. These improved forecasts of the space weather indices help in making actionable, durable conjunction predictions sooner than is currently possible.

Fluid dynamical systems are well described by discretized partial differential equations, but computational costs limit accuracy, duration and/or resolution in numerical integrations. Recent studies showed that deep neural networks trained on simulations or PDE-derived losses can improve cost-accuracy tradeoffs, but purely data-centric approaches discard physical and mathematical insights and require computationally costly training data. Here we draw on advances in geometric deep learning to design solver networks that respect PDE symmetries as hard constraints. We construct equivariant convolutional layers for mixed scalar-vector input fields in order to capture the symmetries inherent to specific PDEs. We demonstrate our approach on a challenging 1D semi-implicit shallow water scheme with closed boundaries, applying unsupervised learning with a physics-derived loss function. We report strong improvements in accuracy and stability of equivariant solvers compared to standard convolutional networks with the same architectures and parameter counts. Solver equivariance also improves performance on new initial conditions not encountered during training, and suppresses error accumulation in global momentum and energy. Strikingly, these benefits do not reduce loss values during training, but appear later during ML-assisted rollouts over time steps. Our results suggest that symmetry constraints could improve deep learning performance across a wide range of fluid dynamical tasks, learning algorithms and neural architectures.

Glancing blows of three interplanetary shocks caused an unexpectedly large magnetic storm on November 4-6, 2023, which was popular for citizen scientists because of the surprising appearance of the crimson-red auroras world-wide in middle latitudes. Based on the analysis of the in-situ interplanetary magnetic field data at DSCOVR and STEREO-A, we show that the multi-step main phase of the magnetic storm is explained by the shock pileup, i.e. slow interplanetary shock was caught up from behind by the fast one, and the multi-step prolonged recovery phase by the remnant structure associated with the shock pileup.

The humidity-dependent acoustic emission (AE) activity in a quartz gouge layer was investigated via sliding-rate step tests. Because AE events are generated by the brittle failure of the contact junction, their activity reflects the micromechanics of friction. AE activity was evaluated by the m-value (characterizing amplitude distribution), AE rate (number of events per unit sliding distance), and their sliding-rate dependences. The m-value decreased with increasing humidity, suggesting contact junction growth by the pressure solution. Increased humidity decreased the AE rate and enhanced the rate-weakening of friction, implying the role of water in suppressing the brittleness of contact junction and strengthening macroscopic instability. Notably, the relationship between the direct effect of friction and the sliding-rate dependence of AE rate under dry conditions was distinct from those under other conditions, suggesting these are sensitivity to areal fraction of the water film on the surface of the gouge particle.

The Superstition Hills Fault (SHF) exhibits a rich spectrum of slip modes, including M 6+ earthquakes, afterslip, quasi-steady creep, and both triggered and spontaneous slow slip events (SSEs). Following 13 years of quiescence, creepmeters recorded 25 mm of slip during 16-19 May 2023. Additional sub-events brought the total slip to 41 mm. The event nucleated on the northern SHF in early-May and propagated bi-laterally at rates on the order of kilometers per day. Surface offsets reveal a bi-modal slip distribution, with slip on the northern section of the fault being less localized and lower amplitude compared to the southern section. Kinematic slip models confirm systematic variations in the slip distribution along-strike and with depth and suggest that slip is largely confined to the shallow sedimentary layer. Observations and models of the 2023 SSE bear a strong similarity to previous slip episodes in 1999, 2006, and 2010, suggesting a characteristic behavior.

In this work, we propose a new generation of high-resolution strain rate model of present-day continental China from up-to-date GNSS observation data of 3571 stations. To reconcile the sparsely distributed GNSS (Global Navigation Satellite System) velocity data into an integrated vastly regional spherical coordinate frame, a novel interpolation method, namely the spherical spline method, is introduced as well. It can simultaneously calculate the strain rate with an ideal order of continuity while preserving the discontinuity from tectonically active major fault zones or deforming blocks. We take advantage of a set of inspection standards to assess the validity and resolution of our proposed model. The spherical spline method is deliberately examined and justified to fit the GNSS velocity data to illustrate inspection standards. Moreover, we construct a spherical harmony model for the resolution test. By the test criteria, the spherical spline method can reproduce the velocity and strain rate field at substantial order, suggesting that our method has high applicability and resolution in estimating strain rate in active tectonic regions or even global models. Finally, using the spherical spline method, we used measured GNSS velocity data to calculate the strain rate field in continental China. We also analyze the correlation between the seismic mechanism and the strain rate field of earthquakes, exhibiting that our proposed high-resolution strain rate model has great potential in explaining the deformation or evolution models of continental China.

Axial Seamount is a submarine volcano on the Juan de Fuca Ridge with enhanced magma supply from the Cobb Hotspot. Here we compare several deformation model configurations to explore how the spatial component of Axial’s deformation time series relates to magma reservoir geometry imaged by multi-channel seismic (MCS) surveys. To constrain the models, we use vertical displacements from pressure sensors at seafloor benchmarks and repeat autonomous underwater vehicle (AUV) bathymetric surveys covering 2016-2020. We show that implementing the MCS-derived 3D main magma reservoir (MMR) geometry with uniform pressure in a finite element model poorly fits the geodetic data. To test the hypothesis that there is compartmentalization within the MMR that results in heterogeneous pressure distribution, we compare analytical models using various horizontal sill configurations constrained by the MMR geometry. Using distributed pressure sources significantly improved the Root Mean Square Error (RMSE) between the inflation data and the models by an order of magnitude. The RMSE between the AUV data and the models was not improved as much, likely due to the relatively larger uncertainty of the AUV data. The models estimate the volume change for the 2016-2020 inter-eruptive inflation period to be between 0.054-0.060 km3 and suggest that the MMR is compartmentalized, with most magma accumulating in sill-like bodies embedded in crystal mush along the western-central edge of the MMR. The results reveal the complexity of Axial’s plumbing system and demonstrate the utility of integrating geodetic data and seismic imagery to gain deeper insights into magma storage at active volcanoes.

Global and coastal ocean surface water elevation prediction skill has advanced considerably with improved algorithms, more refined discretizations and high-performance parallel computing. Model skill is tied to mesh resolution, the accuracy of specified bathymetry/topography, dissipation parameterizations, air-sea drag formulations, and the fidelity of forcing functions. Wind forcing skill can be particularly prone to errors, especially at the land-ocean interface. The resulting biases and errors can be addressed holistically with a machine-learning (ML) approach. Herein, we weakly couple the Temporal Fusion Transformer to the National Oceanic and Atmospheric Administration’s (NOAA) Storm and Tide Operational Forecast System (STOFS 2D Global) to improve its forecasting skill throughout a 7-day horizon. We demonstrate the transformer’s ability to enrich the hydrodynamic model’s output at 228 observed water level stations operated by NOAA’s National Ocean Service. We conclude that the transformer is a rapid way to correct STOFS 2D Global forecasted water levels provided that sufficient covariates are supplied. For stations in wind-dominant areas, we demonstrate that including past and future wind-speed covariates make for a more skillful forecast. In general, while the transformer renders consistent corrections at both tidally and wind-dominant stations, it does so most aggressively at tidally-dominant stations. We show notable improvements in Alaska and the Atlantic and Pacific seaboards of the United States. We evaluate several transformers instantiated with different hyperparameters, covariates, and training data to provide guidance on how to enhance performance.

Monitoring and predicting fault slip behaviors in subduction zones are essential for understanding earthquake cycles and assessing future earthquake potential. We developed a data assimilation (DA) method for fault slip monitoring and short-term prediction of slow slip events (SSEs), which was applied to the 2010 Bungo Channel SSE in southwest Japan. The observed geodetic data were quantitatively explained using a physics-based model with DA. We investigated short-term predictability by assimilating observation data with limited periods. Without prior constraint on fault slip style, observations solely during slip acceleration predicted the occurrence of a fast slip; however, the inclusion of slip deceleration data successfully predicted a slow transient slip. With prior constraint to exclude unstable slip, the assimilation of data after the SSE occurrence predicted a slow transient slip. This study provided a tool using DA for fault slip monitoring and prediction based on real observation data.

A document by Justice Allotey Pappoe. Click on the document to view its contents.

River bifurcations are prevalent features in both gravel-bed and sand-bed fluvial systems, including braiding networks, anabranches and deltas. Therefore, gaining insight into their morphological evolution is important to understand the impact they have on the adjoining environment. While previous investigations have primarily focused on the influence on bifurcation morphodynamics by upstream channels, recent research has highlighted the importance of downstream controls, like branches length or tidal forcing. In particular, in the case of rivers, current linear stability analyses for a simple bifurcation are unable to capture the stabilizing effect of branches length unless a confluence is added downstream. In this work, we introduce a novel theoretical model that effectively accounts for the effects of downstream branch length in a single bifurcation. To substantiate our findings, a series of fully 2D numerical simulations are carried out to test different branches lengths and other potential sources of asymmetries at the node, such as different widths of the downstream channels. Results from linear stability analysis show that bifurcation stability increases as the branches length decreases. These results are confirmed by the numerical simulations, which also show that, as the branch length tends to vanish, bifurcations are invariably stable. Finally, our results interestingly show that, while in general, when a source of asymmetry is present at the node, the hydraulically favoured branch dominates, there are scenarios in which the less-favoured side becomes dominant.

Southwestern Alaska encompasses a group of fault-bounded tectonostratigraphic terranes that were accreted to North America during the Mesozoic and Paleogene. To characterize the offshore extension of these terranes and several significant faults identified onshore, we reprocessed three intersecting multichannel deep seismic reflection profiles totaling ~750 line-km that were shot by the R/V Ewing across part of the inner Bering continental shelf in 1994. Since the uppermost seismic section is often contaminated by high amplitude water layer multiples from the hard and shallow seafloor, the migrated reflection images are supplemented with high-resolution P wave velocity models derived by traveltime tomography of the recorded first-arrivals to depths of up to 2000 m. Additionally, other geophysical datasets such as well logs, ship-board gravity, ship-board magnetics, satellite-altimetry gravity and air-borne magnetics are also incorporated into an integrated regional interpretation. We delineate the offshore extension of the major mapped geological elements, including the Togiak-Tikchik fault, East Kulukak fault, Chilchitna fault, Lake Clarke fault, Togiak terrane, Goodnews terrane, Peninsular terrane, Northern and Southern Kahiltna flysch deposits, and the Regional Suture Zone. We interpret the offshore Togiak-Tikichik fault to be a terrane bounding fault separating the Togiak terrane and Goodnews terrane. We also locate the offshore boundaries of the Regional Suture Zone using satellite gravity anomaly and air-borne magnetic data. Furthermore, we suggest that the sedimentary fill in the graben-like features offshore, as identified by seismic tomographic velocity models, is constituted by the deposits of Northern and Southern Kahiltna flysch.