Crustal structure controls geothermal heat flux which is a key basal boundary conditions for ice-sheet flow in Antarctica. The crustal thickness of Antarctica is well resolved at large-scale, but the smaller-scale structures and density variations in the crust remain poorly constrained. Using 3D gravity inversion constrained by seismic Moho estimates, we model crustal structure in Antarctica, resolving sedimentary basin thickness and density, crustal density and internal layering, and the Moho. Spatial variations in upper crustal density are mapped to radiogenic heat production using a petrophysically-defined mapping approach. Significant variations are observed averaging 1.2 to 1.6 µW/m3, and as high as 2 µW/m3 in West Antarctica. The crustal contribution to geothermal heat flow is similarly variable averaging 18 to 27 mW/m2 and could be up to 60 mW/m2. The mapped variations are significant for correctly representing heat flow in Antarctica.

A minequake of magnitude Mw4.9 occurred on 18 May 2020 early in the morning at the LKAB underground iron ore mine in Kiruna, Sweden. This is the largest mining-induced earthquake in Scandinavia. It generated acoustic signals observed at three infrasound arrays at 9.3 (KRIS, Sweden), 155 (IS37, Norway), and 286 km (ARCI, Norway) distance. Using regional seismic data, we performed a moment-tensor inversion highlighting that this event was dominated by a shallow-depth collapse in agreement with in-mine seismic station data. This was further confirmed by full waveform modelling within a coupled Earth-atmosphere model at local and regional distances using full moment tensor sources. Discrepancies between epicentral location from regional seismic inversion and simulated acoustic data indicate that local pressure records can help further constraining a seismic event location. Numerical simulations demonstrate a potential of using local and regional infrasound data to constrain focal mechanism and depth.

Solidification of the cores of small planets and moons is thought to occur in the â\euro˜iron snowâ\euro™ regime, in which iron crystals form near the core-mantle boundary and fall until re-melting at higher depth. The resulting buoyancy flux may sustain convection and dynamo action. This regime is poorly known, having never been observed in the field or laboratory. Here we present the first laboratory experiments designed to model iron snow. We find that solidification happens in a cyclic pattern, with intense solidification bursts separated by crystal-free periods. This is explained by the necessity of reaching a finite amount of supercooling to re-initiate crystallization once the crystals formed earlier have migrated away. When transposed to planetary cores, our results suggest that crystallization and the associated buoyancy flux would be strongly heterogeneous in time and space, which eventually impacts the time variability and geometry of the magnetic field.

A supervised convolutional neural network (CNN) was developed to automatically identify electromagnetic ion cyclotron (EMIC) wave events from spectrograms. These events have usually been identified manually, which can be a time-consuming process. Statistical analyses of larger datasets would be facilitated if this process were simplified. The neural network model was trained on spectrogram images from the Halley magnetometer station that had been manually identified as either containing or not containing an EMIC wave event anywhere in the spectrogram. This model was tested on an unseen set of spectrograms, achieving a perfect true positive rate of 1. Size, time, frequency, and pixel color information was extracted from each identified event and exported into a spreadsheet for easier analysis. This method has the capability of reducing time and effort required to identify important spectrogram features by hand. Such an automated method could be applied to other space weather data stored in spectrograms.

A document by Aryav Bhesania. Click on the document to view its contents.

Paleomagnetic records of middle Neoproterozoic (820-780 Ma) rocks display high amplitude directional variations that lead to large discrepancies in paleogeographic reconstructions. Hypotheses to explain these data include rapid true polar wander, a geomagnetic field geometry that deviates from a predominantly axial dipole field, a hyper-reversing field (> 10 reversals/Ma), and/or undiagnosed remagnetization. To test these hypotheses, we collected 1057 oriented cores over a 85 m stratigraphic succession in the Laoshanya Formation (Yangjiaping, Hunan, China). High precision U-Pb dating of two intercalated tuff layers constrain the age of the sediments between 809 and 804 Ma. Thermal demagnetization isolates three magnetization components residing in hematite which are not time-progressive but conflated throughout the section. All samples possess a north and downward directed component (in geographic coordinates) at temperatures up to 660°C that is ascribed to a Cretaceous overprint. Two components isolated above 660°C reveal distinct directional clusters: one is interpreted as a depositional remanence, while the other appears to be the result of a mid-Paleozoic (460-420 Ma) remagnetization, which is likely widespread throughout South China. The high-temperature directions are subtly dependent on lithology; microscopic and rock magnetic analyses identify multiple generations of hematite that vary in concentration and distinguish the magnetization components. A comparison with other middle Neoproterozoic paleomagnetic studies in the region indicates that the sudden changes in paleomagnetic directions, used elsewhere to support the rapid true polar wander hypothesis (ca. 805 Ma), are better explained by mixtures of primary and remagnetized components, and/or vertical axis rotations.

Understanding the stress distribution around shallow magma chambers is vital for predicting eruption sites and magma propagation directions. To achieve accurate predictions, comprehensive insight into the stress field surrounding magma chambers and near the surface is essential. Existing stress models for magma chamber inflation often assume a homogenous elastic half-space or a heterogeneous crust with varying mechanical properties in horizontal layers. However, as many volcanoes have complex, non-horizontal, and heterogeneous layers, we enhance these assumptions by considering mechanically diverse layers with varying dips. We employed the Finite Element Method (FEM) to create numerical models simulating two chamber shapes: a circular form and a sill-like ellipse. The primary condition was a 10 MPa excess pressure within the magma chamber, generating the stress field. Layers dips by 20-degree increments, with differing elastic moduli, represented by stiffness ratios (EU/EL) ranging from 0.01 to 100. Our findings validate prior research on heterogeneous crustal modeling, showing that high stiffness ratios disrupt stress within layers and induce local stress rotations at mismatched interfaces. Layer inclination further influences stress fields, shifting the location of maximum stress concentration over varying distances. This study underscores the significance of accurately understanding mechanical properties, layer dip in volcanoes, and magma chamber geometry. Improving predictions of future eruption vents in active volcanoes, particularly in the Andes with its deformed, folded, and non-horizontal stratified crust, hinges on this knowledge. By expanding stress models to incorporate complex geological structures, we enhance our ability to forecast eruption sites and the paths of magma propagation accurately.

Primitive achondrites like the acapulcoites-lodranites (AL) clan are meteorites that formed on bodies in the process of forming a metallic core, providing a unique window into how early solar system processes transformed unmelted material into differentiated bodies. However, the size and structure of the parent body of ALs and other primitive achondrites are largely unknown. Paleomagnetism can establish the presence or absence of a metallic core by looking for evidence of a dynamo magnetic field. We conducted a magnetic study of the Acapulco acapulcoite to determine its ferromagnetic minerals and their recording properties. This is the first detailed rock magnetic and first paleomagnetic study of a primitive achondrite group. We determined that metal inclusions located inside silicate grains consist of two magnetic minerals, kamacite and tetrataenite, which have robust recording properties. However, the mechanisms and timing by which these minerals acquired any natural remanent magnetization are unknown. Despite this, Acapulco has not been substantially remagnetized since arriving on Earth and therefore should retain a record dating to 4.55 billion years ago. Future studies could characterize this record by using high resolution magnetometry measurements of individual grains and developing an understanding of how and when they became magnetized. Our discovery of tetrataenite in ALs provides the first mineralogical evidence for slow cooling (~5 x 103 °C Ma-1) of the AL parent body at low temperatures (~320°C). Its presence means that the AL parent body is unlikely to have been catastrophically disrupted at AL peak temperatures (~1200°C) without subsequent reaccretion.

Structural Analysis Using Integrated Geophysical Methods for Suspected Gold Mineralization within New Peyi Area, Ushafa – Bwari, Abuja, Northcentral Nigeria.Stephen Onuzuruike Udeh1, Patrick N. Dikedi2, Martin Ogharandukun3, Uko Ofe4, Okolo Ikechukwu Thaddeaus 5, and Akinde Aderibigbe 61Department of Pure and Applied Physics, Faculty of Natural and Applied Sciences, Veritas University. Abuja.2Department of Pure and Applied Physics, Faculty of Natural and Applied Sciences, Veritas University. Abuja.3Department of Pure and Applied Physics, Faculty of Natural and Applied Sciences, Veritas University. Abuja.4Department of Pure and Applied Physics, Faculty of Natural and Applied Sciences, Veritas University. Abuja.5National Steel Raw Materials Exploration Agency, Kaduna – Nigeria6Slyvopetro International Limited, Abuja - NigeriaStephen O. Udeh Email: stephenudeh2010@gmail.com †M.Sc. Researcher (Address: National Steel Raw Materials Exploration Agency, No. 18 Rabba Road, Malali – Kaduna, Nigeria)Key Points: Structural Analysis, Integrated Geophysical Methods, Suspected Gold Mineralization

Large earthquakes that occur away from plate boundaries (i.e., large intraplate earthquakes), though rare, could cause heavy damage. Understanding their causes could help with seismic hazard assessment. In this study, we image the seismogenic structure under the 1969 Ms6.4 Yangjiang intraplate earthquake within the stable South China Block with a high-resolution three-dimensional shear-wave velocity model constructed from ambient noise tomography based on a high-density seismic array. The model images relatively low velocities at a fault intersection region from the surface to at least 13 km depth in the Yangjiang seismogenic zone. Given spatial links among the faults, surface seawater, and low velocities, we interpret the low velocities to reflect the presence of seawater-filled highly-fractured rocks in fault zones. We infer that the seawater infiltration could have elevated pore pressure in the long term and lowered effective stress, as evidenced by low earthquake b values at depths of 8-13 km. This process could explain the generation of the Ms6.4 Yangjiang earthquake. We further hypothesize that the large intraplate earthquakes within stable plates are prone to occur in regional weakening regions that tend to build up stress. Given sufficient tectonic stress accumulation, the long-term hydrologically-driven crustal stress variations via increasing pore pressure could play an essential role in triggering large intraplate earthquakes. This study could help seismic hazard assessment in the Guangdong-Hong Kong-Macao-Greater-Bay-Area, China.

Computing the velocity field is an expensive process for mantle convection codes. This has implications for particle methods used to model the advection of quantities such as temperature or composition. A common choice for the numerical treatment of particle trajectories is classical fourth-order Runge–Kutta (ERK4) integration, which involves a velocity computation at each of its four stages. To reduce the cost per time step, it is possible to evaluate the velocity for a subset of the four time integration stages. We explore two such alternative schemes, in which velocities are only computed for: a) stage 1 on odd-numbered time steps and stages 2–4 for even-numbered time steps, and b) stage 1 for all time steps. A theoretical analysis of stability and accuracy is presented for all schemes. It was found that the alternative schemes are first-order accurate with stability regions different from that of ERK4. The efficiency and accuracy of the alternate schemes were compared against ERK4 in four test problems covering isothermal, thermal, and thermochemical flows. Exact solutions were used as reference solutions when available. In agreement with theory, the alternate schemes were observed to be first-order accurate for all test problems. Accordingly, they may be used to efficiently compute solutions to within modest error tolerances. For small error tolerances, however, ERK4 was the most efficient.

Numerous studies have reported the occurrence of aseismic slips or slow slip events along faults induced by fluid injection. However, the underlying physical mechanism and its impact on induced seismicity remain unclear. In this study, we develop a numerical model that incorporates rate-and-state friction fault and fluid injection to simulate the coupled processes of pore pressure diffusion, aseismic slip, and dynamic rupture. We establish a field-scale model to emulate the induced seismicity near the Dallas-Fort Worth Airport, Texas, where events with lower stress drops have been observed. Our numerical calculations reveal that the diffusion of fluid pressure induces aseismic slips and advances or delays seismic ruptures. Furthermore, the stress drops associated with aseismic slips indicate lower values (< 1 MPa), which may explain the observed variation in stress drops near the Airport. Simulations encompassing diverse injection operations and fault frictional parameters show that the interplay between the amount of pore pressure perturbations and stress states during the interseismic period influences the initiation, quantity, recurrence intervals, and source parameters of aseismic slips. However, the scaling relationship of moment (M0) with ruptured domain (r0) for all simulated events follows an unusual trend, M0∝r04.3, similar to M0∝r04.7 observed in the Airport sequence. Based on the consistent scaling, we hypothesize that the lower stress drop events in the Airport may be less dynamic ruptures, similar to aseismic slips as illustrated in our simulations.

We image the high-resolution velocity structures of the crust and uppermost mantle beneath the western part of the Himalayan-Tibetan orogen through tomographic inversion of local and regional earthquake data. We herein reconstruct and present the tomographic image of the variable configuration of the Moho boundary beneath the Himalayan-Tibetan orogen. The thickness of the crust varies between ~40-65 km from south beneath the sub-Himalaya to north beneath the Higher Himalaya. The thickest crust imaged as thick as ~85 km, located ~100 km from ITSZ towards north beneath the southwest Tibet. Our results also report significantly variable geometry of the Moho boundary along the tectonic trend of the Himalayan-Tibetan orogen, which may indicate that the Indian plate subducted/underthrusted beneath the Eurasian plate in a piecewise manner as a consequence of differential convergence rates, counter clockwise rotation of the Indian plate and episodic collision processes. We also image the geometry of the subducting/underthrusting Indian plate beneath the Himalayan-Tibetan orogen. We present the geodynamic model of the two subducted slabs, where the Indian plate subducts/underthrusts towards north and the Tibetan slab subducted southwards beneath the Tibetan plateau. We infer that the Indian plate is torn into pieces differing in its northern limits and angle of subduction/underthrusting. Where its westernmost end subducts/underthrusts below the Eurasian plate with a gentle dip crossing ITSZ and KKMF. On the other hand, towards east the Indian plate subducts/underthrust the Eurasian plate with a relatively greater angle near ITSZ, approximately 250 km distant from HFT.

The topography of ocean worlds is often used to infer ice shell thicknesses by assuming topography is compensated by a basal root. We systematically test the stability of isostatically compensated topography in ice shells. At short horizontal wavelengths, lithospheric strength can support surface topography, while at long wavelengths, buoyancy forces can support topography at the surface and base of the ice shell over geologic time scales. These behaviors are also seen for Airy isostasy in terrestrial worlds. Contrastingly at intermediate scales, the mechanically weak lower ice shell can inhibit the transfer of buoyancy forces to the surface. Factors such as surface temperature can alter the contribution of lithospheric strength, decreasing the stability of a compensating root. This nuanced understanding of icy shell lithospheres provides crucial insights for interpreting surface features and inferring underlying ice shell thickness, with substantial relevance for upcoming space missions to the Jovian system.

The Antarctic ice sheet is buttressed by floating ice shelves that calve icebergs along large fractures called rifts. We report the first-ever seismic recording of a multiple-kilometer rift propagation event located in Pine Island Glacier Ice Shelf. The rift grew 10.5 km at a speed of 34.8 m/s, the fastest known ice fracture at this scale. We simulate ocean-coupled rift propagation and find that hydrodynamics control rupture velocities. During rift propagation, ocean water flows into the rift at a rate of at least 2300 m3/s and causes mixing in the subshelf cavity. Our observations support the hypotheses that large ice shelf rift propagation events are brittle, hydrodynamically limited, and exhibit sensitive coupling with the surrounding ocean.

The Teisseyre-Tornquist Zone (TTZ) is the longest pre-Alpine tectonic lineament in Europe. Its nature and structural evolution are controversially debated. In this study, we show its structural evolution beneath the southern Baltic Sea both on crustal and basin scale by using three seismic reflection profiles combined with 2-D potential field data. The results demonstrate that the southern Baltic Sea is underlain by a thick crust of the East European Craton (EEC) with a Moho depth in the range of 38-42 km. The overall crustal architecture is shaped by three phases of localized crustal stretching in early Paleozoic, Devonian-Carboniferous, and Permian-Mesozoic. The most spectacular feature of the southern Baltic Sea are zones of thick-skinned compressional deformation produced by Alpine inversion along the TTZ and Sorgenfrei-Tornquist Zone (STZ). Both zones include a system of thrusts and back thrusts penetrating the entire crust in an 80-90 km wide inversion zone superimposed on the EEC crust and its sedimentary cover. ENE-vergent thrusts are traced from the top of the Cretaceous down to the Moho and they are accompanied by back thrusts of opposite vergence, also reaching the Moho. Inversion tectonics resulted in the uplift of a block of cratonic crust as a pop-up structure, bounded by thrusts and back thrusts, and the displacement of the Moho within the STZ and TTZ. The similar mechanism of intra-cratonic inversion was recognized for the Dnieper-Donbas Basin in Ukraine, and it may be characteristic of rigid cratons, where deformation is localized in a few preexisting zones of weakness.

The thickness of the seismogenic crust (Ts) controls crustal earthquakes. Its upper limit is the seismicity onset depth (SOD) while its base corresponds to the seismicity cutoff depth (SCD) that correlates with the brittle-ductile transition. Thus, it influences the magnitude and location of crustal earthquakes and knowledge of its geometry may aid in seismic hazard assessment. Here we present the first Ts map of the Andean margin. We follow the standard methodology using the statistical depth distribution of events on a grid of equally size square cells. However, we find it has flaws and develop a new approach, based on circular cells of variable radius that changes according to earthquake density. Our results indicate that Ts is heterogenous, showing three controls: thermal structure, subduction geometry and crustal thickness.

Coupled fire-atmosphere models often struggle to simulate important fire processes like fire generated flows, deep flaming fronts, extreme updrafts, and stratospheric smoke injection during large wildfires. This study uses the coupled fire-atmosphere model, WRF-Fire to examine the sensitivities of some of these phenomena to the modeled surface fuel load. Specifically, the 2020 Bear Fire and 2021 Caldor Fire in California’s Sierra Nevada are simulated using three fuel loading scenarios (1x, 4x, and 8x LANDFIRE derived surface fuel), while controlling the fire rate of spread, to isolate the fuel loading needed to produce fire-generated flows and plume rise comparable to NEXRAD radar observations of these events. Increasing fuel loads and corresponding fire residence time in WRF-Fire leads to deep plumes in excess of 10 km, strong vertical velocities of 40-45 m s-1, and combustion fronts several kilometers in width (in the along wind direction). These results indicate that LANDFIRE-based surface fuel loads in WRF-Fire likely under-represent fuel loading, having significant implications for simulating landscape-scale wildfire processes, associated impacts on spread, and fire-atmosphere feedbacks.