Persistent volcanic activity is thought to be linked to degassing, but volatile transport at depth cannot be observed directly. Instead, we rely on indirect constraints such as CO2-H2O concentrations in melt inclusions trapped at different depth, but this data is rarely straight-forward to interpret. In this study, we develop a multiscale model of conduit flow during passive degassing to identify how flow behavior in the conduit is reflected in melt-inclusion data and surface gas flux. During the approximately steady flow likely characteristic of passive-degassing episodes, variability in degassing arises primarily from two processes, the mixing of volatile-poor and volatile-rich magma and variations in CO2 influx from depth. To quantify how conduit-flow conditions alter mixing efficiency, we first model bidirectional flow in a conduit segment at the scale of tens of meters while fully resolving the ascent dynamics of intermediate-size bubbles at the scale of centimeters. We focus specifically on intermediate-size bubbles, because these are small enough not to generate explosive behavior, but large enough to alter the degree of magma mixing. We then use a system-scale volatile-concentration model to evaluate the joint effect of magma mixing and CO2 influx on volatile concentrations profiles against observations for Stromboli and Mount Erebus. We find that the two processes have distinct observational signatures, suggesting that tracking them jointly could help identify changes in conduit flow and advance our understanding of eruptive regimes.
Although adequately detailed kerosene chemical-combustion Arrhenius reaction-rate suites were not readily available for combustion modeling until ca. the 1990’s (e.g., Marinov ), it was already known from mass-spectrometer measurements during the early Apollo era that fuel-rich liquid oxygen + kerosene (RP-1) gas generators yield large quantities (e.g., several percent of total fuel flows) of complex hydrocarbons such as benzene, butadiene, toluene, anthracene, fluoranthene, etc. (Thompson ), which are formed concomitantly with soot (Pugmire ). By the 1960’s, virtually every fuel-oxidizer combination for liquid-fueled rocket engines had been tested, and the impact of gas phase combustion-efficiency governing the rocket-nozzle efficiency factor had been empirically well-determined (Clark ). Up until relatively recently, spacelaunch and orbital-transfer engines were increasingly designed for high efficiency, to maximize orbital parameters while minimizing fuels and structural masses: Preburners and high-energy atomization have been used to pre-gasify fuels to increase (gas-phase) combustion efficiency, decreasing the yield of complex/aromatic hydrocarbons (which limit rocket-nozzle efficiency and overall engine efficiency) in hydrocarbon-fueled engine exhausts, thereby maximizing system launch and orbital-maneuver capability (Clark; Sutton; Sutton/Yang). The combustion community has been aware that the choice of Arrhenius reaction-rate suite is critical to computer engine-model outputs. Specific combustion suites are required to estimate the yield of high-molecular-weight/reactive/toxic hydrocarbons in the rocket engine combustion chamber, nonetheless such GIGO errors can be seen in recent documents. Low-efficiency launch vehicles also need larger fuels loads to achieve the same launched mass, further increasing the yield of complex hydrocarbons and radicals deposited by low-efficiency rocket engines along launch trajectories and into the stratospheric ozone layer, the mesosphere, and above. With increasing launch rates from low-efficiency systems, these persistent (Ross/Sheaffer ; Sheaffer ), reactive chemical species must have a growing impact on critical, poorly-understood upper-atmosphere chemistry systems.
The propagation of the fast magnetosonic (FMS) wave in the curved magnetic field is studied. A hemicylindrical model of the magnetosphere is considered where the magnetic field lines are represented by concentric circles. An ordinary differential equation is derived describing the coupled Alfv\’en and FMS waves. Using the equation, it was demonstrated that in the curved field the propagation of the fast mode is drastically different from the propagation in the planar magnetic field. In particular, on the magnetic surface known as the reflection surface for the fast mode in the planar magnetic field, there is a wave singularity where some components of the wave’s magnetic field (the azimuthal and compressional components) as well as the plasma density have logarithmic singularity. The physical reason for this singularity is the decrease of the volume of the magnetic flux tube toward the axis of the cylinder.
The Sichuan-Yunnan region is located at the intersection between the South China Block, the Indian plate and the Tibet Plateau and is crisscrossed with deep and large faults and is characterized by strong seismic activities. Here we employ one-year continuous waveforms of the vertical component of 89 broadband seismic stations in this region to evaluate the velocity structure and its implications. Through single station data preprocessing, cross-correlation calculation, stacking, group velocity dispersion measurement and quality evaluation, the group velocity dispersion curves of Rayleigh waves for the different periods were obtained. We then use the surface wave tomography method to obtain the Rayleigh wave group velocity distribution of 9-40s in this area. Finally, the S-wave velocity structure in the depth range of 0-60 km in the study area is obtained by pure path dispersion inversion. The results show that the surface layer or the top of the upper crust in the Sichuan Basin is characterized by low velocity due to the influence of the sedimentary strata, whereas the middle and lower crust of the Sichuan Basin shows high velocity structure. The Sichuan-Yunnan diamond-shaped block (SYDB) shows a high-velocity structure in the middle crust, , and a low velocity in the lower crust. The seismic activities are mainly concentrated at the western part of the region, with the earthquakes distributed at the boundary between the low- and high-velocity structures, as well as the adjacent region, which we correlate with the extrusion of the Tibet Plateau.
Induced seismicity observed during Enhanced Geothermal Stimulation (EGS) at Otaniemi, Finland is modelled using both statistical and physical approaches. The physical model produces simulations closest to the observations when assuming rate-and-state friction for shear failure with diffusivity matching the pressure build-up at the well-head at onset of injections. Rate-and-state friction implies a time dependent earthquake nucleation process which is found to be essential in reproducing the spatial pattern of seismicity. This implies that permeability inferred from the expansion of the seismicity triggering front (Shapiro, 1997) can be biased. We suggest a heuristic method to account for this bias that is independent of the earthquake magnitude detection threshold. Our modelling suggests that the Omori law decay during injection shut-ins results mainly from stress relaxation by pore pressure diffusion. During successive stimulations, seismicity should only be induced where the previous maximum of Coulomb stress changes is exceeded. This effect, commonly referred to as the Kaiser effect, is not clearly visible in the data from Otaniemi. The different injection locations at the various stimulation stages may have resulted in sufficiently different effective stress distributions that the effect was muted. We describe a statistical model whereby seismicity rate is estimated from convolution of the injection history with a kernel which approximates earthquake triggering by fluid diffusion. The statistical method has superior computational efficiency to the physical model and fits the observations as well as the physical model. This approach is applicable provided the Kaiser effect is not strong, as was the case in Otaniemi.
Although adequately detailed kerosene chemical-combustion Arrhenius reaction-rate suites were not readily available for combustion modeling until ca. the 1990’s (e.g., Marinov ), it was already known from mass-spectrometer measurements during the early Apollo era that fuel-rich liquid oxygen + kerosene (RP-1) gas generators yield large quantities (e.g., several percent of total fuel flows) of complex hydrocarbons such as benzene, butadiene, toluene, anthracene, fluoranthene, etc. (Thompson ), which are formed concomitantly with soot (Pugmire ). By the 1960’s, virtually every fuel-oxidizer combination for liquid-fueled rocket engines had been tested, and the impact of gas phase combustion-efficiency governing the rocket-nozzle efficiency factor had been empirically well-determined (Clark ). Up until relatively recently, spacelaunch and orbital-transfer engines were increasingly designed for high efficiency, to maximize orbital parameters while minimizing fuels and structural masses: Preburners and high-energy atomization have been used to pre-gasify fuels to increase (gas-phase) combustion efficiency, decreasing the yield of complex/aromatic hydrocarbons (which limit rocket-nozzle efficiency and overall engine efficiency) in hydrocarbon-fueled engine exhausts, thereby maximizing system launch and orbital-maneuver capability (Clark; Sutton; Sutton/Yang). The rocket combustion community has been aware that the choice of Arrhenius reaction-rate suite is critical to computer engine-model outputs. Specific combustion suites are required to estimate the yield of high-molecular-weight/reactive/toxic hydrocarbons in the rocket engine combustion chamber, nonetheless such GIGO errors can be seen in recent documents. Low-efficiency launch vehicles (SpaceX, Hanwha) therefore also need larger fuels loads to achieve the same launched/transferred mass, further increasing the yield of complex hydrocarbons and radicals deposited by low-efficiency rocket engines along launch trajectories and into the stratospheric ozone layer, the mesosphere, and above. With increasing launch rates from low-efficiency systems, these persistent (Ross/Sheaffer ; Sheaffer ), reactive chemical species must have a growing impact on critical, poorly-understood upper-atmosphere chemistry systems.
Complex fault systems are often located in regions with asymmetric topography on one side of a fault, and these systems are very common in Southern California. Along these fault systems, geometrical complexities such as stepovers can impact fault rupture. Previous rupture dynamic studies have investigated the effect of stepover widths on throughgoing rupture, but these studies didn’t examine the influence of topography on the rupture behavior. To investigate the effect of asymmetric topography on rupture dynamics at stepovers, I consider three cases: 1) a flat topography, 2) a positive (mountain) and 3) a negative (basin) topography on only one side of the fault system outside of the stepover. In each case, I use the 3D finite element method to compute the rupture dynamics of these fault systems. The results show a significant time dependent variation of the normal stress for the topography cases as opposed to the flat surface case, which can have an important impact on rupture propagation at the stepover. For a positive topography on the right of the rupture propagation, there is a clamping effect behind the rupture front that prevents the rupture to jump a wider extensional stepover. The opposite is observed for a negative topography or for a positive topography on the left side of the rupture propagation, where the rupture can jump over a wider compressional stepover. These results suggest that topography should be considered in dynamic studies with geometric complexities such as stepovers, and perhaps bends and branched fault systems.
Despite being exposed to convective stresses for much of the Earth's history, cratonic roots appear capable of resisting mantle shearing. This tectonic stability can be attributed to the neutral density and higher strength of cratons. However, the excess thickness of cratons and their higher viscosity amplify coupling to underlying mantle flow, which could be destabilizing. To investigate the stresses that a convecting mantle exerts on cratons that are both strong and thick, we developed instantaneous global spherical numerical models that incorporate present-day geoemetry of cratons within active mantle flow. Our results show that mantle flow is diverted downward beneath thick and viscous cratonic roots, giving rise to a ring of elevated and inwardly-convergent tractions along a craton’s periphery. These tractions induce regional compressive stress regimes within cratonic interiors. Such compression could serve to stabilize older continental lithosphere against mantle shearing, thus adding an additional factor that promotes cratonic longevity.
A weather station in Nukuʻalofa (NUKU), Tonga, ~68km away from the epicenter of the 2022 Tonga eruption, recorded exceptional pressure, temperature, and wind data representative of the eruption source hydrodynamics. These high-quality data are available for further source and propagation studies. In contrast to other barometers and infrasound sensors at greater ranges, the NUKU barometer recorded a decrease in pressure during the climactic stage of the eruption. A simple fluid dynamic explanation of the depressurization is provided, with a commentary on near- vs far-field pressure observations of very large eruptions.
Western Indian Ocean basin shows one of the most complex signatures of the ocean floor anomalies by juxtaposition of the rapidly evolving, multiple spreading ridges, subduction systems and microcontinental slivers. This study based on ocean floor magnetic anomalies, gravity gradient map, tomographic profiles and geometrical kinematic models reports a significant westward drift of the Central Indian Ridge (CIR) segments. Documented precisely between the latitudes 17°S and 21°S the drift is coincident with the Deccan volcanism at ~65±2 Ma and we further explain its bearing on the Indian plate kinematics. The progressive stair-step trend of the ridge segments towards NE is marked by anomalous deflection to NW for a brief distance of ~217 km between these latitudes represented by the anomalies C30n-C29n. The observed length of the ridge segments moving NW at 17°S match the calculated NW drift rates of Indian plate (Bhagat et al., 2022). We infer that the NW drift and its restoration towards NE triggered short Plume Induced Subduction Initiation along the Amirante trench. Further a plume induced lithospheric tilt of the Indian plate (Sangode et al 2022) led to restoration of subduction along the Sunda trench at ~65 Ma imparting new slab pull force over the Indian subcontinent besides the NE trend for CIR. This episode resulted into anticlockwise rotation of the Indian plate along with accelerated drift rates due to vector addition of the plume push and the slab pull forces from Eurasian as well as Sunda subduction systems after 65 Ma. The Deccan eruption thus resulted in major geodynamic reorganization that altered the kinematics of Indian plate; and the signatures of which are well preserved over the ocean floor.
Self-organizing diffusion-reaction systems naturally form complex patterns under far from equilibrium conditions. A representative example is the rhythmic concentration pattern of Fe-oxides in Zebra rocks; these patterns include reddish-brown stripes, rounded rods, and elliptical spots. Similar patterns are observed in the banded iron formations which are presumed to have formed in the early earth under global glaciation. We propose that such patterns can be used directly (e.g., by computer-vision-analysis) to infer basic quantities relevant to their formation giving information on generalized chemical gradients. Here we present a phase-field model that quantitatively captures the distinct Zebra rock patterns based on the concept of phase separation that describes the process forming Liesegang stripes. We find that diffusive coefficients (i.e., the bulk self-diffusivities and the diffusive mobility of Cahn-Hilliard dynamics) play an essential role in controlling the appearance of regular stripe patterns as well as the transition from stripes to spots. The numerical results are carefully benchmarked with the well-established empirical spacing law, width law, timing law and the Matalon-Packter law. Using this model, we invert for the important process parameters that originate from the intrinsic material properties, the self-diffusivity ratio and the diffusive mobility of Fe-oxides, with a series of Zebra rock samples. This study allows a quantitative prediction of the generalized chemical gradients in mineralized source rocks without intrusive measurements, providing a better intuition for the mineral exploration space.
The polar cap can become teardrop shaped through the poleward expansion of the dusk and dawn sectors of the auroral oval, to form what is called horse collar aurora (HCA). The formation of HCA has been linked to dual-lobe reconnection (DLR) where magnetic flux is closed at the dayside magnetopause. A prolonged period of northward IMF is required for the formation of HCA. HCA have previously been identified in UV images captured by the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument on-board the Defense Meteorological Satellite Program (DMSP) spacecraft F16, F17 and F18. Events that have concurrent 630.0 nm all-sky camera (ASC) data from the Redline Geospace Observatory (REGO) Resolute Bay site are now studied in more detail, making use of the higher cadence of the ASC images compared to DMSP/SSUSI. 11 HCA events are studied and classified based on the IMF conditions at the end of the event. Five of the events were found to end via a southward turning of the IMF, two end with positive By dominated IMF and four with negative By dominance. Under positive (negative) By the arcs move duskward (dawnward) in the northern hemisphere with the opposite true in the southern hemisphere. Under a southward turning the arcs move equatorward. One event is of particular interest as it occurred while there was a transpolar arc (TPA) also present. Understanding the evolution of HCA will allow DLR to be studied in more detail.
One of the most prominent plate tectonic processes is seafloor spreading. But its formation processes are poorly understood. In this study, we thoroughly address how the brittle-ductile weakening process affects the formation and development of tectonic patterns at spreading centers using 3D magmatic-thermomechanical numerical models. Grain size evolution and brittle/plastic strain weakening are fully coupled into the model. A spectrum of tectonic patterns, from asymmetric long-lived detachment faults in rolling-hinge mode, short-lived detachment faults in flip-flop mode, to symmetric conjugate faults in flip-flop mode are documented in our models. Systematic numerical results indicate that fault strength reduction and axial brittle layer thickness are two pivotal factors in controlling the faulting patterns and spreading modes. Strain weakening induced by localized hydrothermal alteration can lead to the variation of the fault strength reduction. Strong strain weakening with large fault strength reduction results in very asymmetric detachment faults developing in rolling-hinge mode, while weak strain weakening leads to small fault strength reduction, forming conjugate faults. Moreover, the thermal structure beneath the ridge is influenced by spreading rates, hydrothermal circulation, and mantle potential temperature, which in turn controls the thickness of the axial brittle layer and results in variation in tectonic patterns. Further, in order to test a damage mechanism with a physical basis, we investigate grain size reduction at the root of detachment faults. We found that its effect in the formation of detachment faults appears to play a subordinate role compared to brittle/plastic strain weakening of faults.
The effects of sphericity are regularly neglected in numerical and laboratory studies that examine the factors controlling subduction dynamics. Most existing studies have been executed in a Cartesian domain, with the small number of simulations undertaken in a spherical shell incorporating plates with an oversimplified rheology, limiting their applicability. Here, we simulate free-subduction of composite visco-plastic plates in 3-D Cartesian and spherical shell domains, to examine the role of sphericity in dictating the dynamics of subduction, and highlight the limitations of Cartesian models. We identify two irreconcilable differences between Cartesian and spherical models, which limit the suitability of Cartesian-based studies: (i) the presence of sidewall boundaries in Cartesian models, which modify the flow regime; and (ii) the reduction of space with depth in spherical shells, alongside the radial gravity direction, which cannot be captured in Cartesian domains. Although Cartesian models generally predict comparable subduction regimes and slab morphologies to their spherical counterparts, there are significant quantitative discrepancies. We find that simulations in Cartesian domains that exceed Earth’s dimensions overestimate trench retreat. Conversely, due to boundary effects, simulations in smaller Cartesian domains overestimate the variation of trench curvature driven by plate width. Importantly, spherical models consistently predict higher sinking velocities and a reduction in slab width with depth, particularly for wider subduction systems, enhancing along-strike slab buckling and trench curvature. Results imply that sphericity must be considered when simulating Earth’s subduction systems, and that it is essential for accurately predicting the dynamics of subduction zones of width ~2400 km or more.
Models of the high-latitude ionospheric electric field are commonly used to specify the magnetospheric forcing in thermosphere or whole atmosphere models. The use of decades-old models based on spacecraft data is still widespread. Currently the Heelis and Weimer climatology models are most commonly used but it is possible a more recent electric field model could improve forecasting functionality. Modern electric field models, derived from radar data, have been developed to incorporate advances in data availability. It is expected that climatologies based on this larger and up-to-date dataset will better represent the high latitude ionosphere and improve forecasting abilities. An example of two such models, which have been developed using line-of-sight velocity measurements from the Super Dual Auroral Radar Network (SuperDARN) are the Thomas and Shepherd model (TS18), and the Time-Variable Ionospheric Electric Field model (TiVIE). Here we compare the outputs of these electric field models during the September 2017 storm, covering a range of solar wind and interplanetary magnetic field (IMF) conditions. We explore the relationships between the IMF conditions and the model output parameters such as transpolar voltage, the polar cap size and the lower latitude boundary of convection. We find that the electric potential and field parameters from the spacecraft-based models have a significantly higher magnitude than the SuperDARN-based models. We discuss the similarities and differences in topology and magnitude for each model.
In the text “Electricity and Magnetism”, I propose a hypothesis about the whole mechanism for electricity and magnetism and their interactions, including the discussions about followings: 1, the possible existence of magnetic charges in protons and electrons where the positive and negative electric charges locate exactly; 2, the mechanism of the activation and deactivation of magnetic charges with in protons and electrons; 3, how electricity, magnetism and Lorentz effect interact with each other within hydrogen atom; The whole mechanism can provide a framework for hydrogen atom and solve the atomic stability issue.
On the edge of our continents, oceanic crust meets continental crust. At passive margins, those where there is no active tectonics, subduction or transform faulting, these crustal types are connected as sharp continent-ocean boundaries (COB) or as diffuse continent-ocean transition (COT) zones. Passive margins are hard to explore and consequently relatively little is known about their morphology or the processes of their formation. Here we elicit and analyse seismic image interpretations of the passive margin offshore East India conducted by 17 groups of geoscientists to better understand the differences, or lack therein, of COB or COT interpretations of the margin. The group interpretations provide a wide range of margin models, five of which are abrupt COB based and 11 which are diffuse COT based. However, interpretations within the COB set vary in the placement of the boundary line between continental and oceanic crust, the boundary placement lying within the range of interpreted COT zones, with the average COB location falling in the centre of the interpreted COT zones. These crowd-sourced results are then compared with ten published interpretations across the margin, which show COB and COT zones falling in the same area. These findings raise questions as to the real differences in COB and COT models and the geological processes involved in their formation. Considering this, we discuss the implications for passive margin models and the use of Wisdom of Crowds-type approaches in reflecting on both the range of interpretation-based models and in the value of determining ‘average’ model approaches.