A document by Brook Tozer. Click on the document to view its contents.

Seasonal frozen ground freeze-thaw cycles in cold regions are an essential indicator of climate change, infrastructure, and ecosystems in the near-surface critical zone (CZ). As a non-invasive geophysical method, the ambient noise seismic method estimates the relative velocity variations (dv/v) based on coda waves or ballistic waves, providing new insights into the seasonal frozen ground changes in the soil properties and hydrology data, such as soil moisture content (SMC), temperature, and groundwater level. Due to the dv/v lack of accurate depth information and average over tens of days at low frequencies, it is challenging to provide the needed temporal-spatial resolution for the micrometer-level frozen ground variation. In this work, we combine the 1D linear three-component seismic array and hydrological sensor to conduct seasonal frozen ground freeze-thaw monitoring experiments. Besides the conventional dv/v information, we calculate surface-wave (SW) dispersion curve variations (dc/c), which are more sensitive to SMC and can characterize the daily air temperature variations. Meanwhile, the horizontal-to-vertical spectral ratio (HVSR) amplitude and seismic attenuation also show highly consistent changes to the freeze-thaw processes. This work demonstrates that the different ambient noise seismic information (dc/c, HVSR, and attenuation) provide robust observations for hydrogeological monitoring, such as air temperature, SMC, and groundwater level changes during seasonal freeze-thaw processes.

On 8 October 2023 UTC, significant tsunamis were observed around Japan without any major tsunamigenic earthquake, associated with a series of 14 successive minor earthquakes (mb = 4.5–5.4) near Sofugan in the Izu-Bonin islands. To examine the cause of this tsunami, we estimated the horizontal locations of the tsunami source and temporal history of the seafloor displacement, using the tsunami data recorded by the ocean-bottom pressure gauges > ~600 km away. Our results showed the main tsunami source was an uplift located at a caldera-like bathymetric feature near Sofugan, suggesting the involvement of caldera activity in the tsunami generation. The total seafloor uplift was larger than ~3 m, and the uplift amount of each event gradually increased over time, reflecting an accelerating occurrence of multiple sudden caldera uplifts within only a few hours.

Spacecraft magnetic field measurements are able to tell us much about the planets’ interior dynamics, composition, and evolutionary timeline. Magnetic fields also serve as the source for passive magnetic sounding of moons. Time-varying magnetic fields experienced by the moons, due to relative planetary motion, interact electrically with conductive layers within these bodies (including salty subsurface oceans) to produce induced magnetic fields that are measurable by nearby, magnetometer-equipped spacecraft. Many factors influence the character of the induced field, including the precise amplitude and phase of the time-varying field, known as the excitation or driving field and represented by excitation moments. In this work, we present an open-source software package named PlanetMag that features calculation of planetary magnetic field models available in the literature at arbitrary positions and times. The implemented models enable simultaneous inversion of the excitation moments across a range of oscillation frequencies using linear least-squares methods and ephemeris data with the SPICE toolkit. Here we summarize the available magnetic field models and their associated coordinate systems. Precisely-determined excitation moments are a critical input to forward models of global induced fields. Our results serve as a prerequisite to any precise comparison to spacecraft data for magnetic sounding investigation of giant planet moons—connecting the induced magnetic field to a moon’s interior requires accurate representation of the oscillating excitation field. We calculate complex excitation moments relative to the J2000 epoch and share the results as ASCII tables compatible with MoonMag or other software packages intended for induction response calculations.

The application of deep-learning-based seismic phase pickers for earthquake monitoring has surged in recent years. However, the efficacy of these models when applied to monitoring volcano seismicity has yet to be evaluated. Here, we first compile a dataset of seismic waveforms from various volcanoes globally. We then show that the performances of two widely used deep-learning pickers deteriorate systematically as the earthquakes’ frequency content decreases. Therefore, the performances are especially poor for long-period earthquakes often associated with fluid/magma movement. Subsequently, we train new models which perform significantly better, including when tested on volcanic earthquake waveforms from northern California where no training data are used and tectonic low-frequency earthquakes along the Nankai Trough. Our model/workflow can be applied to improve monitoring of volcano seismicity globally while our compiled dataset can be used to benchmark future methods for characterizing volcano seismicity, especially long-period earthquakes which are difficult to monitor.

This study presents a novel approach to modeling the Earth’s geomagnetic field, which originates from electric currents approximately 2,900 km beneath the surface, crucial for understanding planetary dynamics. We introduce a method for inverting a planetary-scale equivalent magnetization source and develop a 3-D equivalent electric current circulation model from this source, enhancing understanding of these deep currents. This research signifies the first use of unstructured tetrahedral magnetization inversion technology for planet-scale magnetic data interpretation and equivalent source model construction. Validated through a synthetic case study, the method is applied to the International Geomagnetic Reference Field (IGRF) and SWARM satellite datasets, comprising 35,768 magnetic vectors from two orbital altitudes. Employing various mesh configurations, we construct and compare detailed current source models from these datasets. The effectiveness of our equivalent current sources is confirmed by comparison with dynamo research findings, demonstrating significant advancements in geomagnetic field modeling, particularly in interpretability, and providing novel insights into Earth’s magnetic phenomena.

A document by PRARABDH TIWARI. Click on the document to view its contents.

The Karakoram fault is an important strike-slip boundary for accommodating deformation following the India-Asia collision. However, whether the deformation is confined to the crust or whether it extends into the mantle remains highly debated. Here, we show that the Karakoram fault is overwhelmingly dominated by crustal degassing related to a 4 He-and CO 2rich fluid reservoir [e.g., He contents up to ~1.0−1.6 vol.%; 3 He/ 4 He = 0.029 ± 0.016 R A (1σ, n = 50); CO 2 /N 2 up to 3.7−57.8]. Crustal-scale active deformation driven by strike-slip faulting could mobilize 4 He and CO 2 from the fault zone rocks, which subsequently accumulate in the hydrothermal system. The Karakoram fault may have limited fluid connections to the mantle, and if any, the accumulated crustal fluids would efficiently dilute the uprising mantle fluids. In both cases, crustal deformation is evidently the first-order response to strike-slip faulting.

Tsunamis are rare, destructive events, whose generation, propagation and coastal impact processes involve several complex physical phenomena. Most tsunami applications, like probabilistic tsunami hazard assessment, make extensive use of large sets of numerical simulations, facing a systematic trade-off between the computational costs and the modelling accuracy. For seismogenic tsunami, the source is often modelled as an instantaneous sea-floor displacement due to the fault static slip distribution, while the propagation in open-sea is computed through a shallow water approximation. Here, through 1D earthquake-tsunami coupled simulations of large M>8 earthquakes in Tohoku-like subduction zone, we tested for which conditions the instantaneous source (IS) and/or the shallow water (SW) approximations can be used to simulate with enough accuracy the whole tsunami evolution. We used as a reference a time-dependent (TD), multi-layer, non-hydrostatic (NH) model whose source features, duration, and size, are based on seismic rupture dynamic simulations with realistic stress drop and rigidity, within a Tohoku-like environment. We showed that slow ruptures, generating slip in shallow part of subduction slabs (e.g. tsunami earthquakes), and very large events, with an along-dip extension comparable with the trench-coast distance (e.g. mega-thrust) require a TD-NH modelling, in particular when the bathymetry close to the coast features sharp depth gradients. Conversely, deeper, higher stress-drop events can be accurately modelled through an IS-SW approximation. We finally showed to what extent inundation depend on bathymetric geometrical features: (i) steeper bathymetries generate larger inundations and (ii) a resonant mechanism emerges with run-up amplifications associated with larger source size on flatter bathymetries.

The Archean Superior craton was formed by the assemblage of continental and oceanic terranes at ∼2.6 Ga. The craton is surrounded by multiple Proterozoic mobile belts, including the Paleoproterozoic Trans-Hudson Orogen which brought together the Superior and Rae/Hearne cratons at ∼1.9-1.8 Ga. Despite numerous studies on Precambrian lithospheric formation and evolution, the deep thermochemical structure of the Superior craton and its surroundings remains poorly understood. Here we investigate the upper mantle beneath the region from the surface to 400 km depth by jointly inverting Rayleigh wave phase velocity dispersion data, elevation, geoid height and surface heat flow, using a probabilistic inversion to obtain a (pseudo-)3D model of composition, density and temperature. The lithospheric structure is dominated by thick cratonic roots (>300 km) beneath the eastern and western arms of the Superior craton, with a chemically depleted signature (Mg# > 92.5), consistent with independent results from mantle xenoliths. Beneath the surrounding Proterozoic and Phanerozoic orogens, the Mid-continent Rift and Hudson Strait, we observe a relatively thinner lithosphere and more fertile composition, indicating that these regions have undergone lithospheric modification and erosion. Our model supports the hypothesis that the core of the Superior craton is well-preserved and has evaded lithospheric destruction and refertilization. We propose three factors playing a critical role in the craton’s stability: (i) the presence of a mid-lithospheric discontinuity, (ii) the correct isopycnic conditions to sustain a strength contrast between the craton and the surrounding mantle, and (iii) the presence of weaker mobile belts around the craton.

Fluid flow through fractured media is typically governed by the distribution of fracture apertures, which are in turn governed by stress. Consequently, understanding subsurface stress is critical for understanding and predicting subsurface fluid flow. Although laboratory-scale studies have established a sensitive relationship between effective stress and bulk electrical conductivity in crystalline rock, that relationship has not been extensively leveraged to monitor stress evolution at the field scale using electrical or electromagnetic geophysical monitoring approaches. In this paper we demonstrate the use time-lapse 3-dimensional (4D) electrical resistivity tomography to image perturbations in the stress field generated by pressurized borehole packers deployed during shear-stimulation attempts in a 1.25 km deep metamorphic crystalline rock formation.

The objectives of this paper are to investigate the tradeoffs between a physically constrained neural network and a deep, convolutional neural network and to design a combined ML approach (“VarioCNN”). Our solution is provided in the framework of a cyberinfrastructure that includes a newly designed ML software, GEOCLASS-image, modern high-resolution satellite image datasets (Maxar WorldView data) and instructions/descriptions that may facilitate solving similar spatial classification problems. Combining the advantages of the physically-driven connectionist-geostatistical classification method with those of an efficient CNN, VarioCNN, provides a means for rapid and efficient extraction of complex geophysical information from submeter resolution satellite imagery. A retraining loop overcomes the difficulties of creating a labeled training data set.Computational analyses and developments are centered on a specific, but generalizable, geophysical problem: The classification of crevasse types that form during the surge of a glacier system. A surge is a glacial catastrophe, an acceleration of a glacier to typically 100-200 times its normal velocity, which for a marine-terminating glacier leads to sudden and substantial mass transfer from the cryosphere to the oceans, contributing significantly to sea-level-rise. The sudden and rapid acceleration characteristic of a surge results in formation of crevasses, whose spatial characteristics provide informants on the ice-dynamic processes that occur during the surge. GEOCLASS-image is applied to study the current (2016-2024) surge in the Negribreen Glacier System, Svalbard. The geophysical result is a description of the structural evolution and expansion of the surge, based on crevasse types that capture ice deformation in 6 simplified classes.

A document by Lukas Bohsung. Click on the document to view its contents.

Arctic permafrost thaw holds the potential to drastically alter the Earth’s surface in Northern high latitudes. We utilize high-resolution Large Eddy Simulations to investigate the impact of the changing surfaces onto the neutrally stratified Atmospheric Boundary Layer (ABL). A stochastic surface model based on Gaussian Random Fields modeling typical permafrost landscapes is established in terms of two land cover classes: grass land and open water bodies, which exhibit different surface roughness length and surface sensible heat flux. A set of experiments is conducted where two parameters, the lake areal fraction and the surface correlation length, are varied to study the sensitivity of the boundary layer with respect to surface heterogeneity. Our key findings from the simulations are the following: The lake areal fraction has a substantial impact on the aggregated sensible heat flux at the blending height. The larger the lake areal fraction, the smaller the sensible heat flux. This result gives rise to a potential feedback mechanism. When the Arctic dries due to climate heating, the interaction with the ABL may accelerate permafrost thaw. Furthermore, the blending height shows significant dependency on the correlation length of the surface features. A longer surface correlation length causes an increased blending height. This finding is of relevance for land surface models concerned with Arctic permafrost as they usually do not consider a heterogeneity metric comparable to the surface correlation length.

• MARSIS radar sounder data reveals layering in the Medusae Fossae Formation deposits. • Layers are likely due to transitions between mixtures of ice-rich and ice-poor dust, analogous to those in Polar Layered Deposits. • An ice-rich portion of the MFF deposit may contain the largest volume of water in the equatorial region of Mars.

Surface deformation associated with continental earthquake ruptures includes localized deformation on the faults, as well as deformation in the surrounding medium though distributed and/or diffuse processes. However, the connection of the diffuse part of the surface deformation to the overall rupture process, as well as its underlying physical mechanisms are not yet well understood. Computing high-resolution optical image correlations for the 2021/05/21 Mw7.4 Maduo, Tibet, rupture, we highlight a correlation between the presence of faults and fractures at the surface, and variations in the across-fault displacement gradient, fault zone width, and amplitude of surface displacement. We show that surface slip along primary faults is systematically associated with gradients greater than 1%, and is dominant in regions of greater coseismic surface displacement. Conversely, the diffuse deformation is associated with gradients ≤0.3%, and is dominant in regions of lesser surface displacement. The distributed deformation then occurs for intermediate gradients of 0.3-1%, and at the transition between the localized and diffuse deformation regions. Such patterns of deformation are also described in laboratory experiments of rock deformation, themself supported by field observations. Comparing these experiments to our observations, we demonstrate that the diffuse deformation along the 2021 Maduo rupture corresponds to kilometer-wide plastic yielding of the bulk medium occurring in regions where surface rupture is generally missing. Along the 2021 Maduo rupture, diffuse deformation occurs primarily in the epicentral region, where the dynamic stresses associated with the nascent pulse-like rupture could not overcome the shallow fault zone frictional strength.

We analyzed time-of-flight (TOF) data from the Arase satellite to investigate temporal variations of O2+, NO+, and N2+ at 19.2 keV/q in the inner magnetosphere for 6.5 years from the solar declining to rising phases. Molecular ion counts were estimated by subtracting the background contamination of oxygen counts. While the number of clear molecular events was small, the estimated molecular ion counts exhibited good correlation with the solar wind dynamic pressure and SYM-H index. Long-term variations of molecular ions were different from that of oxygen ions. Additionally, we discuss the importance of the solar wind dynamic pressure in causing the escape of molecular ions into the magnetosphere through an increase in the convection electric field, which causes different evolutions of oxygen ions and molecular ions.

This work aims at presenting how we have developed the ShakeMap Atlas of historical earthquakes in Italy through the following steps: 1. the collection of macroseismic data for a selected dataset of historical Italian earthquakes with magnitudes equal to or greater than 6. 2. the adoption of two different ShakeMap configurations. 3. the application of the iterative leave-one-out cross-validation procedure within ShakeMap to identify the most appropriate configuration. 4. the analysis of the results. Acknowledgements A d d your information, graphs and images to this section.

The asthenosphere is commonly defined as an upper mantle zone with low velocities and high attenuation of seismic waves, and high electrical conductivity. These observations are usually explained by the presence of partial melt, or by a sharp contrasts in the water content of the upper mantle. Low viscosity asthenosphere is an essential ingredient of functioning plate tectonics. We argue that a substantial component of asthenospheric weakening is dynamic, caused by dislocation creep at the base of tectonic plates. Numerical simulations of subduction show that dynamic weakening scales with the surface velocity both below the subducting and the overriding plate, and that the viscosity decrease reaches up to two orders of magnitude. The resulting scaling law is employed in an apriori estimate of the lateral viscosity variations (LVV) below Earth’s oceans. The obtained LVV helps in explaining some of the long-standing as well as recent problems in mantle viscosity inversions.

Mesoscale-to-microscale coupling is an important tool to conduct turbulence-resolving multiscale simulations of realistic atmospheric flows, which are crucial for applications ranging from wind energy to wildfire spread studies. Different techniques are used to facilitate the development of realistic turbulence in the large-eddy simulation (LES) domain while minimizing computational cost. Here, we explore the impact of a simple and computationally efficient Stochastic Cell Perturbation method using momentum perturbation (SCPM-M) to accelerate turbulence generation in boundary-coupled LES simulations using the Weather Research and Forecasting (WRF) model. We simulate a convective boundary layer (CBL) to characterize the production and dissipation of turbulent kinetic energy (TKE) and the variation of TKE budget terms. Furthermore, we evaluate the impact of applying momentum perturbations of three magnitudes below, up to, and above the CBL on the TKE budget terms. Momentum perturbations greatly reduce the fetch associated with turbulence generation. When applied to half the vertical extent of the boundary layer, momentum 1 perturbations produce an adequate amount of turbulence. However, when applied above the CBL, additional structures are generated at the top of the CBL, near the inversion layer. The magnitudes of the TKE budgets produced by SCPM-M when applied at varying heights and with different perturbation amplitudes are always higher near the surface and inversion layer than those produced by No-SCPM, as are their contributions to the TKE. This study provides a better understanding of how SCPM-M reduces computational costs and how different budget terms contribute to TKE in a boundary-coupled LES simulation.

A document by Hilary Chang. Click on the document to view its contents.

Micromagnetic modelling allows the systematic study of the effects of particle size and shape on the first-order reversal curve (FORC) magnetic hysteresis response for magnetite particles in the single-domain (SD) and pseudo-single domain (PSD) particle size range. The interpretation of FORCs, though widely used, has been highly subjective.  Here, we use micromagnetics to model randomly oriented distributions of particles to allow more physically meaningful interpretations.  We show that one commonly found type of PSD particle - namely single vortex (SV) particles - has far more complex signals than SD particles, with multiple peaks and troughs in the FORC distribution, where the peaks have higher switching fields for larger SV particles. Particles in the SD to SV transition zone have the lowest switching fields. Symmetrical and prolate particles display similar behavior, with distinctive peaks forming near the vertical axis of the FORC diagram. In contrast, highly oblate particles produce `butterfly' structures, suggesting that these are potentially diagnostic of particle morphology. We also consider FORC diagrams for distributions of particle sizes and shapes and produce an online application that users can use to build their own FORC distributions.  There is good agreement between the model predictions for distributions of particle sizes and shapes, and the published experimental literature.

Mapping of the basement relief in regions of a high geological importance is key to mineral prospecting. In this study, we estimate the sediment thickness within the Southern Benue Trough of Nigeria by using synthetic Bouguer gravity data alongside 113 logged borehole data to validate the gravimetric inversion and interpretation. A 3-D gravimetric inversion of the residual gravity data was carried out to determine the thickness of sedimentation after a regional-residual gravity separation. Our numerical results (ranging from 0.8 to 5.5 km) have almost no systematic bias (mean value = 0.045) when compared with the 113 measured sediment depths obtained from drilling profiles. The estimated sediment depths closely mimic the known geological structures and tectonic complexities of the highly rifted Southern Benue Trough of Nigeria. The synthetic Bouguer gravity map exhibits a spatial pattern that indicates possible magmatic movements, which could have led to shallow sediments over and along the Abakaliki Anticlinorium. This elevated crust (because of an upward magmatic movement) created crevices, faults, folds, ridges, or troughs that must have paved way for a thick sedimentary cover that possibly have matured overtime (because of a high temperature) into important habitats for mineral resources. We conclude that the very thick sedimentary cover at the southwestern portion of the study area may have been brought about by a compaction or compression of tectonic plates thereby generating adequate heat and pressure for the maturation of several mineral resources at the Southern Benue Trough of Nigeria.   Keyword: Bouguer gravity maps; gravity inversion; sediment thickness; Regional-residual gravity separation; mineral exploration

Deep Martian aquifers harboring liquid water could hold vital insights for current and past habitability. We show that with seismo-electric interface responses (IRs) we can quantitatively characterize subsurface water on Mars. Full-waveform simulations and sensitivity analyses across diverse Martian aquifer scenarios demonstrate the technique’s effectiveness. In contrast to how seismo-electric signals often appear on Earth, Mars’ desiccated surface naturally removes co-seismic fields and exposes useful IRs that allow us to characterize several aquifer properties. Changing the aquifer depth, thickness, or quantity changes the IR arrival times or shape: aquifer depth is a strong control on evanescent IRs, thickness affects the relative timing of IRs, and increasing the number of aquifers introduces more dipole sources to the waveform. Other factors, such as aquifer saturation, chemistry, and salinity, strongly affect IR amplitude but have minimal or no effect on waveform shape. Notably, for a deep low-porosity aquifer, the salinity and brine chemistry (perchlorate versus chloride) are the strongest controls on signal amplitude. Analyzing the effects of epicentral distance shows that radiating and evanescent IRs separate at large source-receiver offset, allowing analyses of both signals and accurate event distance derivation. From this numerical investigation of the sensitivity of IRs to deep Martian aquifers, we anticipate future analyses of electromagnetic data from the InSight lander or future missions to Mars and other planets.