To help meet emission standards, hydrogen sulfide (H2S) from geothermal production may be injected back into the subsurface, where basalt offers, in theory, the capacity to mineralize H2S into pyrite. Ensuring the viability of this pollution mitigation technology requires information on how much H2S is mineralized, at what rate and where. To date, monitoring efforts of field-scale H2S reinjection have mostly occurred via mass balance calculations, typically capturing less than 5\% of the injected fluid. While these studies, along with laboratory experiments and geochemical models, conclude effective H2S mineralization, their extrapolation to quantify mineralization and its persistence over time leads to considerable uncertainty. Here, a geophysical methodology, using time-domain induced polarization (TDIP) logging in two of the injection wells (NN3 and NN4), is developed to follow the fate of H2S re-injected at Nesjavellir geothermal site in south-west Iceland. Results show a strong chargeability increase at +40 days, corresponding to precipitation of up to 1\% in NN4 and 2\% in NN3 according to laboratory-based relationships. A uniform increase is observed along NN4, whereas it is localized below 450 in NN3. Changes are more pronounced with the larger electrode spacing, indicating that pyrite precipitation takes place away from the wells. Furthermore, a chargeability decrease is observed at later monitoring rounds in both wells, suggesting that pyrite is either passivated or re-dissolved after precipitating. These results highlight the ability of TDIP logging to monitor pyrite mineralization and have implications for understanding the fate of H2S upon subsurface storage in basaltic environments.

We are developing a new approach to earthquake nowcasting based on science transformers (GC Fox et al., Geohazards, 2022). As explained in the seminal paper by Vaswani et al. (NIPS, 2017), a transformer is a type of deep learning model that learns the context of a set of time series values by means of tracking the relationships in a sequence of data, such as the words in a sentence. Transformers extend deep learning in the adoption of a context-sensitive protocol "attention", which is used to tag important sequences of data, and to identify relationships between those tagged data. Pretrained transformers are the foundational technology that underpins the new AI models ChatGPT (Generative Pretrained Transformers) from openAI.com, and Bard, from Google.com. In our case, we hypothesize that a transformer might be able to learn the sequence of events leading up to a major earthquake. Typically, the data used to train the model is in the billions or larger, so these models, when applied to earthquake problems, need the size of data sets that only long numerical earthquake simulations can provide. In this research, we are developing the Earthquake Generative Pretrained Transformer model, "QuakeGPT", in a similar vein. For simulations, we are using simulation catalogs from the physics-based model Virtual Quake, the statistical model ETAS, and a statistical physics model based on invasion percolation. Observed data, which is the data to anticipate with nowcasting, is taken from the USGS online catalog for California. In this talk, we discuss the architecture of QuakeGPT and report first results. We also report results using other types of simulated seismicity such as slider block models, to quantify how well a Wednesday, 13 December 2023 14:45-14:55 2016-West (Level 2, West, Moscone Center) Nowcasting Earthquakes with QuakeGPT: An AI-Enhanced Earthquak.

A document by María Constanza Manassero. Click on the document to view its contents.

Venus boasts an abundance of volcano and volcano-like structures. Synthetic aperture radar images of the surface have revealed extensive evidence of volcanism, including lava flows and edifices. Volcanic activity is further supported by crater statistics, and analysis of topography and gravity data. Unique to Venus, coronae are quasi-circular, volcano-tectonic features exhibiting diverse volcanic characteristics. Despite this, volcanism is often under-represented in formation models. We identify a new subset of coronae that display topographic change subsequent to the emplacement of lava flows within their fracture annuli, pointing to the critical role of volcanism in the formation of these coronae. Through spherical-harmonic distribution analysis, we find that this new subset is spatially related to the full coronae database, pointing to an intrinsic process of coronae formation. Furthermore, coronae exhibit strong correlations and similar spectral shapes at low spherical harmonic degrees with large volcanoes, suggesting a shared geodynamic origin. Our findings underscore the pivotal role of volcanism in coronae formation and highlight the need for future research that integrates magmatic processes into geophysical models.

A document by Taiyi Wang. Click on the document to view its contents.

Earthquake magnitude is controlled by the rupture area of the fault network hosting the event. For surface-rupturing large strike-slip earthquakes (~MW6+), ruptures must overcome zones of geometrical complexity along fault networks. These zones, or earthquake gates, act as barriers to rupture propagation. We map step-overs, bends, gaps, splays, and strands from the surface ruptures of 31 strike-slip earthquakes, classifying each population into breached and unbreached groups. We develop a statistical model for passing probability as a function of geometry for each group. Step-overs, and single bends are more predictable earthquake gates than double bends and gaps, and ~20% of ruptures terminate on straight segments. Based on our modeled probabilities, we estimate event likelihood as the joint passing probabilities of breached gates and straight segments along a rupture. Event likelihood decreases inversely with rupture length squared. Our findings support a barrier model as a factor in limiting large earthquake size.

In various research fields such as hydrogeology, environmental science and energy engineering, geological formations with fractures are frequently encountered. Accurately characterizing these fractured media is of paramount importance when it comes to tasks that demand precise predictions of liquid flow and the transport of solute and energy within them. Since directly measuring fractured media poses inherent challenges, data assimilation (DA) techniques are typically employed to derive inverse estimates of media properties using observed state variables like hydraulic head, concentration, and temperature. Nonetheless, the considerable difficulties arising from the strong heterogeneity and non-Gaussian nature of fractured media have diminished the effectiveness of existing DA methods. In this study, we formulate a novel DA approach known as PEDL (parameter estimator with deep learning) that harnesses the capabilities of DL to capture nonlinear relationships and extract non-Gaussian features. To evaluate PEDL’s performance, we conduct two numerical case studies with increasing complexity. Our results unequivocally demonstrate that PEDL outperforms three popular DA methods: ensemble smoother with multiple DA (ESMDA), iterative local updating ES (ILUES), and ES with DL-based update (ESDL). Sensitivity analyses confirm PEDL’s validity and adaptability across various ensemble sizes and DL model architectures. Moreover, even in scenarios where structural difference exists between the accurate reference model and the simplified forecast model, PEDL adeptly identifies the primary characteristics of fracture networks.

Coalescence of magnetic flux ropes (MFRs) is suggested as a crucial mechanism for electron acceleration in various astrophysical plasma systems. However, how electrons are being accelerated via MFR coalescence is not fully understood. In this paper, we quantitatively analyze electron acceleration during the coalescence of three MFRs at Earth’s magnetopause using in-situ Magnetospheric Multiscale (MMS) observations. We find that suprathermal electrons are enhanced in the coalescing MFRs than those in the ambient magnetosheath and non-coalescing MFRs. Both first-order Fermi and E|| acceleration were responsible for this electron acceleration, while the overall effect of betatron mechanism decelerated the electrons. The most intense Fermi acceleration was observed in the trailing part of the middle MFR, while E|| acceleration occurred primarily at the reconnection sites between the coalescing MFRs. For non-coalescing MFRs, the dominant acceleration mechanism is the E|| acceleration. Our results further consolidate the important role of MFR coalescence in electron acceleration in space plasma.

Ultra-low velocity zones (ULVZs) above the core-mantle boundary (CMB) are significant structures that connect the lowermost mantle and outer core. As “thin patches” of dramatically low seismic-wave velocity, they are occasionally found near the base of mantle plumes and in-or-near high seismic-wave speed regions above the CMB. The causes of their morphological distribution and geodynamics remain unclear, and simulation results of high-density melts diverge from seismic observations. We introduced a two-dimensional time-dependent Stokes two-phase flow (with melt migration) numerical model to investigate the formation and morphological characteristics of ULVZs caused by CMB-mantle tangential flows and a neighboring cold source (subducted plate). We discovered that (a) the participation of cold sources with temperature differences between ~4000 K at the plume central regions to <~3900 K at the plume-cooling mantle region, separated by horizontal distances of approximately 100 (±<50) km are necessary for the stable existence of dense melts with mass-density difference >+1–2% (even +10%) with respect to the surrounding mantle; additionally, (b) an enhanced tangential flow coincident with the internal reverse circulation within the broad plume base (with speeds >3 times the lowermost-mantle characteristic flow speed) are necessary for higher aspect-ratio-morphology lenses compatible with seismic observations. The CMB-mantle tangential flow and/or outer-core interacting with CMB-topography may help generate mega-ULVZs, particularly if they appear along the edges of large low-shear-wave-velocity provinces (LLSVPs) and in/near high seismic-speed “cold” zones. Thus, we infer that a strong link exists between ULVZ morphology and the dynamic environment of the lowermost mantle and uppermost outer core.

A document by Oumeng Zhang. Click on the document to view its contents.

Microfluidic devices with open lattice structures, equivalent to a type of porous media, allow for the manipulation of fluid transport processes while having distinct structural, mechanical, and thermal properties. However, a fundamental understanding of the design principles for the solid structure in order to achieve consistent and desired flow patterns remains a challenge, preventing its further development and wider applications. Here, through quantitative and mechanistic analyses of the behavior of multi-phase phenomena that involve gas-liquid-solid interfaces, we present a design framework for a new class of microfluidic devices containing porous architectures (referred to as poroFluidics) for deterministic control of multi-phase fluid transport processes. We show that the essential properties of the fluids and solid, including viscosity, interfacial tension, wettability, as well as solid manufacture resolution, can be incorporated into the design to achieve consistent flow in porous media, where the desired spatial and temporal fluid invasion sequence can be realized. Experiments and numerical simulations reveal that different preferential flow pathways can be controlled by solid geometry, flow conditions, or fluid/solid properties. Our design framework enables precise, multifunctional, and dynamic control of multi-phase transport within engineered porous media, unlocking new avenues for developing cost-effective, programmable microfluidic devices for manipulating multi-phase flows. 

The coupling between subducted slabs and trailing plates is often conceptualised in terms of a net in-plane force. If a significant fraction of upper-mantle slab buoyancy (e.g. ~ 25%) were transferred in this manner, a net in-plane force on the order of 5-10 TN/m would be typical of the trailing plates. Results from a numerical subduction model are presented here which question both the magnitude and-perhaps more profoundly-the mode of force transmission. In this model the subducting plate (SP) driving force is predominantly supplied by differences in gravitational potential energy (GPE). The GPE associated with plate downbending (flexural topography) provides about half the total driving force. The magnitude of the trench GPE is related to the amplitude of topography, but is mediated by the internal stress distributions associated with bending. Above the elastic core, the stress is Andersonian and vertical normal stresses are lithostatic. This implies horizontal gradients in the vertical normal stress, across columns of different elevation in the outer slope. The bulk of the trench GPE arises from this upper, extensional section the lithosphere. Vertical shear stress (and horizontal gradients thereof) are concentrated in the elastic core of the slab, where principal stresses rotate through 90 degrees. In this region, horizontal gradients in vertical normal stress rapidly diminish; they fully equilibrate at about twice the neutral plane depth. For the deepest trenches on Earth, these relationships imply trench GPE of up to about 5 TN/m. The model demonstrates that mantle slabs can drive plate tectonics simply through downbending, where the predominant mode of slab-plate coupling is via the vertical shear force and bending moment. 

The Cenozoic evolution of the Himalaya-Tibet Plateau, dictated by the India-Asia convergence, remains a subject of substantial ambiguity. Here, a thermo-mechanical model is used to show the critical controls of decelerating convergence on the formation and stabilization of distinctive tectonic structures during prolonged collision. At high constant convergence rates, similar to the late Paleogene India-Asia motions, the lower plate crust is injected beneath the overriding crust, uplifting a plateau, first, then is exhumed towards the orogeny front. Conversely, low constant convergence rates, similar to the Neogene India-Asia motions, induce crustal thickening and plateau formation without underplating or exhumation of incoming crust. Strikingly, models simulating the decelerating India-Asia convergence history portray a dynamic evolution, highlighting the transitory nature of features under decreasing convergence, as the orogen shifts to a new equilibrium. In the transitional phase, the slowing of convergence decreases basal shearing and compression, leading to extension and heating in the orogen interiors. This allows diapiric ascent of buried crust and plateau collapse, as accretion migrates to a frontal fold-and-thrust belt. The models provide insights into the multi-stage evolution of the long-lived Himalayan-Tibetan orogeny, from fast early growth of the Tibetan Plateau, through its transient destabilisation and late-stage internal extension, behind the expanding Himalayan belt.

A document by Yuta Tsusaka. Click on the document to view its contents.

The first-order configuration of the Himalayan orogen is defined by the northward motion of the Indian Plate, whether directly "underplating" under the Tibetan crust or "subducting" beneath a mantle wedge. Our 3D S-wave receiver-functions newly reveal orogen-perpendicular tearing or warping of the Indian Plate. West of 90°E, the southern limit of the Tibetan lithosphere-asthenosphere boundary is at the Indian crustal front, ~100-km north of the Yarlung-Zangbo suture, implying an underplating of the intact Indian lithosphere beneath Tibet. Further east, the delaminated Indian lithospheric mantle during its gravitationally-induced rollback is separated from the Indian crust by an interposed asthenospheric wedge. The nascent Tibetan lithosphere and its subjacent thin asthenosphere continue ~100 km south of the Yarlung-Zangbo suture. This contrast in lithospheric structures across the Yadong-Gulu and Cona-Sangri rifts at 90-92°E, in 2 agreement with helium isotopic anomalies and deep seismicity, requires the subducting Indian Plate be warped or torn.

Dipolarizing flux bundles (DFBs) have been suggested to transport energy and momentum from regions of reconnection in the magnetotail to the high latitude ionosphere, where they can generate localized ionospheric currents that can produce large nighttime geomagnetic disturbances (GMDs). In this study we identified DFBs observed in the midnight sector from ~7 to ~10 RE by THEMIS A, D, and E during days in 2015-2017 whose northern hemisphere magnetic footpoints mapped to regions near Hudson Bay, Canada, and have compared them to GMDs observed by ground magnetometers. We found six days during which one or more of these DFBs coincided within ± 3 min with ≥ 6 nT/s GMDs observed by latitudinally closely spaced ground-based magnetometers located near those footpoints. Spherical elementary current systems (SECS) maps and all-sky imager data provided further characterization of two events, showing short-lived localized intense upward currents, auroral intensifications and/or streamers, and vortical perturbations of a westward electrojet. On all but one of these days the coincident DFB – GMD pairs occurred during intervals of high-speed solar wind streams but low values of SYM/H. In some events, in which the DFBs were observed closer to Earth and with lower Earthward velocities, the GMDs occurred slightly earlier than the DFBs, suggesting that braking had begun before the time of the DFB observation. This study is the first to connect spacecraft observations of DFBs in the magnetotail to intense (>6 nT/s) GMDs on the ground, and the results suggest DFBs could be an important driver of GICs.

We investigated the effects of the propagation path and site amplification of shallow tremors along the Nankai Trough. Using far-field S-wave propagation from intraslab earthquake data, the amplification factors at the DONET stations were 5–40 times against an inland outcrop rock site. Thick (~5 km) sedimentary layers with VS of 0.6–2 km/s beneath DONET stations have been confirmed by seismological studies. To investigate the effects of thick sedimentary layers, we synthesized seismograms of shallow tremors and intraslab earthquakes at seafloor stations. The ratios of the maximum amplitudes from the synthetic intraslab seismograms between models with and without thick sedimentary layers were 1–2. This means that the estimated large amplifications are primarily controlled by thin lower-velocity (< 0.6 km/s) sediments just below the stations. Conversely, at near-source (≤ 20 km) distances, 1-order amplifications of seismic energies for a shallow tremor source can occur due to thick sedimentary layers. Multiple S-wave reflections between the seafloor and plate interface are contaminated in tremor envelopes; consequently, seismic energy and duration are overestimated. If a shallow tremor occurs within underthrust sediments, the overestimation becomes stronger because of the invalid rigidity assumptions around the source region. After 1-order corrections of seismic energies of shallow tremors along the Nankai Trough, the scaled energies of seismic slow earthquakes were 10-10–10-9 irrespective of the region and source depth. Hence, the physical mechanisms governing seismic slow earthquakes can be the same, irrespective of the region and source depth.

Numerous studies have reported that surface hydrological loading can seasonally modulate seismicity rates at crustal depths. For example, substantial winter snow accumulation occurs across the Japanese Islands, and these snowy regions appear to have seasonally modulated the occurrence of previous large inland earthquakes. Therefore, it is important to investigate the impact of seasonal stress changes on crustal seismicity to deepen our understanding of earthquake generation. Here we constrain seasonal changes in the surface load across northeastern Japan using Global Navigation Satellite System surface displacements and evaluate the potential relationship between temporal trends in inland seismicity and estimated seasonal stress changes. The spatial distribution of the seasonal surface load is consistent with snow depth along the Sea of Japan. The inland seismicity beneath northeastern Japan is modestly modulated by the seasonal stress changes that are induced by the annual snow load. However, this seasonal response is weaker than that in other regions. This weak modulation may be due to the small surface-load-induced stress perturbation relative to the long-term-averaged stressing rate and/or the limited presence of crustal fluids to trigger seismicity in Japan.

Kumar et al. (2023) in their article discuss and highlight the complexities involved in the comparison of long-term and short-term ongoing deformation in the Northwest Himalaya and their influence over the topographic evolution of the region. Their observations that rely largely on the GNSS geodetic results (Kumar et al., 2023) have also been the basis of conclusions presented in a companion paper by Malik et al., 2023a. The conclusions presented in the latter-mentioned paper have been questioned in a rejoinder by Singh and Rajendran (2023) and defended by Malik et al. (2023b). Below we present pointwise inconsistencies in the present study (Kumar et al., 2023) and the conclusions presented therein. We present our differing observations of the two segments of the fault system called the ‘Khetpurali-Taksal’ Fault (KTF-1 and KTF-2), as discussed in the paper by Kumar et al. (2023)

Super Dual Auroral Radar Network (SuperDARN) consists of more than 30 monostatic high-frequency (HF, 10-18~MHz) radars which utilise signals scattered from decameter-scale ionospheric irregularities for studying dynamic processes in the ionosphere. By combining line-of-sight velocity measurements of ionospheric scatter echoes from radars with overlapping fields of view, SuperDARN provides maps of ionospheric plasma drift velocity over mid and high latitudes. The conventional SuperDARN radars consecutively scan through sixteen beam directions with dwelling time of 3.5 s/beam, which places a lower limit of one minute to sample the entire field of view. In this work we remove this limitation by utilizing advanced capabilities of the recently developed Borealis digital SuperDARN radar system. Combining a wide transmission beam with multiple narrow reception beams allows us to sample all conventional beam directions simultaneously and to increase the sampling rate of the entire field of view by up to sixteen times without noticeable deterioration of the data quality. The wide-beam emission also enabled the implementation of multistatic operations, where ionospheric scatter signals from one radar are received by other radars with overlapping viewing areas. These novel operations required the development of a new model to determine the geographic location of the source of the multistatic radar echoes. Our preliminary studies showed that, in comparison with the conventional monostatic operations, the multistatic operations provide a significant increase in geographic coverage, in some cases nearly doubling it. The multistatic data also provide additional velocity vector components increasing the likelihood of reconstructing full plasma drift velocity vectors.

This study explores geomorphology within canyons using 3D seismic imaging. It reveals crucial insights that underscore the relationship between growth faults, slope instability, and canyon development. The structural settings of canyons, often conforming to established patterns, come to light as integral components of the study. An important observation was made: the gradient, a first-order factor, exerts significant control over both canyon initiation and propagation. Furthermore, the distribution of growth faults, a major catalyst for slope instability, holds an indirect yet profound link to sediment routing within canyons and the ancient geography of the region. These findings not only enhance our understanding of canyon evolution but also play a crucial role in interpreting reservoir distribution, marking them as invaluable assets in some geological exploration and reservoir management. 

An important component of quantifying bedload transport flux is the identification of the onset of bedload motion. Bedload transport can be monitored with high temporal resolution using passive acoustic methods, e.g., hydrophones. Yet, an efficient method for identifying the onset of bedload transport from long-term continuous acoustic data is still lacking. Benford’s Law defines a probability distribution of the first-digit of datasets and has been used to identify anomalies. We apply Benford’s Law to the three years of acoustic recordings from a stationary hydrophone in the Taroko National Park, Taiwan. Our workflow allows for monitoring bedload motion in near-real-time, and it is convenient for others to reference. Two bedload transport events were identified during the examined period, lasting 17 and 45 hours, accounting for approximately 0.35% of the time per year.

Basal crevasses threaten the stability of ice shelves through the potential to form rifts and calve icebergs. Different existing fracture theories lead to distinct calving predictions. Furthermore, it is important to determine the dependence of crevasse stability on temperature due to large vertical temperature variations on ice shelves. In this work, we explore the transition from basal crevasses to full thickness fractures considering the vertical temperature structure. Nye’s Zero-Stress approximation violates Newton’s second law. By upholding horizontal force balance, it has been shown analytically that the threshold stress for rift initiation is that of a freely- floating unconfined ice tongue. We generalize the force balance argument to show that while temperature structure influences crack depths, the threshold rifting stress is insensitive to temperature. In the classical Nye’s theory, basal crevasses would develop into rifts at a stress twice of that in our Nye’s theory adhering to horizontal force balance.

A document by Luciana Bonatto. Click on the document to view its contents.