We use seismic ambient noise recorded by dense ocean bottom nodes (OBNs) in the Gorgon gas field, Western Australia, to compute time-lapse seafloor models of shear-wave velocity. The extracted hourly cross-correlation (CC) functions in the frequency band 0.1 – 1 Hz contain mainly Scholte waves with very high signal to noise ratio. We observe temporal velocity variations (dv/v) at the order of 0.1% with a peak velocity change of 0.8% averaged from all station pairs, from the conventional time-lapse analysis with the assumption of a spatially homogeneous dv/v. With a high-resolution reference (baseline) model from full waveform inversion of Scholte waves, we present an elastic wave equation based double-difference inversion (EW-DD) method, using arrival time differences between the reference and time-lapsed Scholte waves, for mapping temporally varying dv/v in the heterogeneous subsurface. The time-lapse velocity models reveal increasing/decreasing patterns of shear-wave velocity in agreement with those from the conventional analysis. The velocity variation exhibits a ~24-hour cycling pattern, which appears to be inversely correlated with sea level height, possibly associated with dilatant effects for porous, low-velocity shallow seafloor and rising pore pressure with higher sea level. This study demonstrates the feasibility of using dense passive seismic surveys for quantitative monitoring of subsurface property changes in the horizontal and depth domain.

The Paleocene-Eocene Thermal Maximum (PETM) was a transient global warming event recognised in the geologic record by a prolonged negative carbon isotope excursion (CIE). The onset of the CIE was the result of a rapid influx of 13C-depleted carbon into the ocean-atmosphere system. However, the mechanisms required to sustain the negative CIE remains unclear. Previous studies have identified enhanced mobilisation of petrogenic organic carbon (OCpetro) and argued that this was likely oxidised, increasing atmospheric carbon dioxide (CO2) concentrations after the onset of the CIE. With existing evidence limited to the mid-latitudes and subtropics, we determine whether: (i) enhanced mobilisation and subsequent burial of OCpetro in marine sediments was a global phenomenon; and (ii) whether it occurred throughout the PETM. To achieve this, we utilised a lipid biomarker approach to trace and quantify OCpetro burial in a global compilation of PETM-aged shallow marine sites (n = 7, including five new sites). Our results confirm that OCpetro mass accumulation rates (MARs) increased within the subtropics and mid-latitudes during the PETM, consistent with evidence of higher physical erosion rates and intense episodic rainfall events. The high-latitude sites do not exhibit distinct changes in the organic carbon source during the PETM. This may be due to the more stable hydrological regime and/or additional controls. Crucially, we also demonstrate that OCpetro MARs remained elevated during the recovery phase of the PETM. Although OCpetro oxidation was likely an important positive feedback mechanism throughout the PETM, we show that this feedback was both spatially and temporally variable.

The heavily faulted Martian terrains of Ceraunius Fossae and Tractus Fossae, south of the Alba Mons volcano, have previously only been considered as parts of larger tectonic studies of Alba Mons, and the complexity of the faulting remains consequently unclear. As these terrains are in midst of the large Tharsis’ volcanoes, the study of their surface deformation has the potential to help unravel the volcano-tectonic deformation history associated with the growth of Tharsis, as well as decipher details of the responsible magma-tectonic processes. In this study, we distinguish between faults and collapse structures based on image and topographic evidence of pit-crater chains. We mapped ~12,000 faults, which we grouped into 3 distinct fault groups based on orientation, morphology, and relative ages. These show a temporal evolution in the mapped fault orientations from NE to NS to NW, with associated perpendicular stress orientations. Collapse features were also mapped and categorized into 4 different groups: pit-crater chains, catenae, u-shaped troughs and chasma. Examining the 4 collapse structures reveals that they are likely 4 different steps in the erosional evolution of pit-crater chains. Together this revealed a structural history heavily influenced by both local (radial to Alba Mons, Pavonis Mons and Ascraeus Mons) and regional (Tharsis radial) lateral diking, and vertical diking from a proposed Ceraunius Fossae centred magma source. This, along with an updated crater size-frequency distribution analysis of the unit ages, reveals a highly active tectonic and magmatic environment south of Alba Mons, in the Late Amazonian.

The tempo of subduction-related magmatic activity over geological time is episodic. Despite intense study and their importance in crustal addition, the fundamental driver of these episodes remains unclear. We demonstrate quantitatively a first order relationship between arc magmatic activity and subduction flux. The volume of oceanic lithosphere entering the mantle is the key parameter that regulates the proportion of H2O entering the sub-arc. New estimates of subduction zone H2O budgets over the last 150 million-years indicate a three- to five-fold increase in the proportion of H2O entering the sub-arc during the most recent global pulse of magmatism. Step changes in H2O flux enable proportionally greater partial melting in the sub-arc. Similar magmatic pulses in the ancient Earth could be related to variability in subduction flux associated with supercontinent cycles.

To effectively reduce CO2 emissions, it’s vital to identify and quantify their sources. While the focus has been on CO2 from fossil fuel combustion, especially coal, the CO2 produced from coal’s other elements, such as sulfur, through chemical reaction, remains an ‘invisible’ carbon source. We analyzed the invisible carbon flux due to coal burning in the Xijiang River Basin, a highly industrialized region in China, using river sulfate fluxes. Dissolved sulfate concentration in the Xijiang River rose by over 300% from 1985 to 2011, largely due to coal combustion. In 2011, this resulted in 3.14 Mt of invisible carbon dioxide. We evaluated the impact of two flue gas desulfurization (FGD) methods on carbon emissions using a predictive model. By enhancing SO2 removal efficiency through these methods, China could cut invisible carbon emissions by 27.8 Mt CO2 annually, paving the way for a sustainable future.

The Klamath Mountains in northern California and southern Oregon are thought to record 200+ m.y. of subduction and terrane accretion, whereas the outboard Franciscan Complex records classic ocean-continent subduction along the North American margin. Unraveling the Klamaths’ late history could help constrain this transition in subduction style. Key is the Mesozoic Condrey Mountain Schist (CMS), comprising, in part, a subduction complex that occupies a structural window through older, overlying central Klamath thrust sheets but with otherwise uncertain relationships to other, more outboard Klamath or Franciscan terranes. The CMS consists of two units (upper and lower), which could be correlated with 1) other Klamath terranes, 2) the Franciscan, or 3) neither based on regional structures and limited extant age data. Upper CMS protolith and metamorphic dates overlap with other Klamath terranes, but the lower CMS remains enigmatic. We used multiple geochronometers to constrain the timing of lower CMS deposition and metamorphism. Maximum depositional ages (MDAs) derived from detrital zircon geochronology of metasedimentary rocks are 153-135 Ma. Metamorphic ages from white mica K-Ar and Rb-Sr multi-mineral isochrons from intercalated and coherently deformed metamafic lenses are 133-116 Ma. Lower CMS MDAs (<153 Ma) predominantly postdate the age of other Klamath terranes, but subduction metamorphism appears to predate the earliest coherent Franciscan underplating (ca. 123 Ma). The lower CMS thus occupies a spatial and temporal position between the Klamaths and Franciscan and preserves a non-retrogressed record of the Franciscan Complex’s early history (>123 Ma), otherwise only partially preserved in retrogressed Franciscan high grade blocks.

The magnitude (MW) 6.6 earthquake that struck Masbate Island on 18 August 2020 offers a unique opportunity to investigate the slip and seismic behavior of the Philippine Fault in the Masbate region. In this study, we employ InSAR, seismicity analysis, and field investigations to comprehensively characterize the coseismic and postseismic slip associated with the event. Our findings reveal a 50-km-long fault rupture along the Masbate segment of the Philippine Fault, with ~23 km surface rupture mapped onshore, despite the occurrence of interseismic creep. The slip distribution demonstrates decreasing displacements northwestward towards the creeping section, with a maximum left-lateral displacement of 0.97 m near the epicenter. Toward the southeast offshore, the rupture terminates at a fault left stepover. While the surface rupture appears relatively straight and narrowly concentrated, the secondary ruptures and mapped offshore faults reveal a more complex transtensional fault structure in the vicinity of Cataingan Bay. This fault complexity represents an asperity that facilitates high-stress accumulation and rupture initiation. Postseismic slip persists for several months along the onshore creeping segment. We derived a slip rate of 2.8 to 4.3 cm/year from long-term and short-term slip measurements. Furthermore, we calculated a recurrence interval of 16 to 41 years for earthquakes similar to the 2020 Masbate earthquake.  Our study highlights how heterogeneity in fault properties, including geometry and coupling state, influences the distribution of slip and magnitude of earthquakes. The 2020 Masbate earthquake provides valuable insights into the rupture dynamics and fault behavior of the Philippine Fault in the Masbate region.

In sparsely fractured crystalline rock, aperture variability exhibits significant control of the flow field through the fracture network. However, its inclusion in models is hampered due to a lack of field measurements and adequate numerical representation. A model for aperture generation is developed based on self-affine methods which includes two key parameters, the Hurst exponent and a scaling parameter, and which accounts for relative anisotropy and correlation between the adjacent surfaces forming the fracture. A methodology for analysing and extracting the necessary parameters from 3D surface scans of natural rock fractures is also developed. Analysis of the Hurst exponent and scaling parameter space shows that input combinations following a linear upper bound can be used to generate aperture fields which accurately reproduce measurements. It is also shown that the Hurst and scaling parameters are more sensitive than the correlation between the upper and lower fracture surfaces. The new model can produce an aperture ensemble that closely corresponds with the aperture obtained from the surface scans, and is an improvement on previous methods. The model is also successfully used to up-scale fracture apertures based on measurements restricted to a small sub-section of the sample. Thereby, the aperture fields generated using the model are representative of natural fracture apertures and can be implemented in larger scale fracture network models, allowing for numerical simulations to included representation of aperture internal heterogeneity.

A document by Sergio León-Ríos. Click on the document to view its contents.

Deltas and fluvial fans are two fan-shaped landforms with complex channel networks. Deltas always occur where rivers enter a standing body of water, such as lakes or oceans. Fluvial fans are inland terrestrial landforms that may form thousands of kilometers from shorelines. Fluvial fans may however also reach lakes and oceans. The current state of knowledge lacks understanding of their morphometric differences or recognition criteria, despite their socioeconomic significance, vulnerability to natural hazards, and important differences in how these landforms respond to global climate change. Moreover, numerous fan-shaped landforms with channel networks have been identified on other planetary bodies, such as Mars and the Saturn's moon Titan, where deltas are important indicators of paleo-shorelines and offer attractive targets for mission sites due to their habitability and high biosignature preservation potential. Here we review the known morphometrics of delta and fluvial fan channel networks, and the differences in their formative processes, and develop morphometric criteria for distinguishing deltas and fluvial fans. We present an ensemble of quantitative metrics that distinguish deltas and fluvial fans and test these criteria on 80 modern channel networks on Earth. Our results improve mechanistic understanding of the fluvial record and delta evolution, provide criteria for accurate recognition of these landforms on planetary bodies and in the sedimentary record, and explain differences in their vulnerabilities to global change.

North of the Denali Fault, the collision between the Yakutat block with North America is accommodated by a fold-thrust belt that gives rise to the northern Alaska Range foothills. At the western end of the belt, the Kantishna Hills anticline hosts prominent microseismicity and surface deformation, together interpreted as active folding of the Kantishna Hills anticline above a midcrustal detachment. Here, we test for such a detachment by using anisotropy-aware receiver functions to image fabric contrasts within the crust and comparing the depths of such contrasts to seismicity statistics. Seismic stations near the crest of the Kantishna Hills anticline and near its southern flank show a single strong contrast in dipping fabric at depths of 12 and 13 km, near where the microseismicity clusters at depth and consistent with a detachment plane beneath the fold. A minimum in b-value at 10-13 km depth is consistent with seismicity on the detachment, compatible with the imaged anisotropic contrast, while off-fault seismicity is shallower, deeper, and limited to smaller magnitudes. South-dipping imbricate thrusts in schist characterize the northern Alaska Range foothills structure and support our interpretation of the observed anisotropy as reflecting SSW-SSE-dipping foliation above a detachment at ~10-13 km depth that may exploit existing crustal weaknesses along more subtle fabric contrasts observed in the seismically quiescent region north of the actively deforming belt.

In the central Tibetan Plateau, an east-west trending band of basins is developed. How such topography formed and the underlying geodynamic processes are still in debate. Magnetotelluric data were collected across the Lunpola basin to study the crustal structure beneath central Tibet. Phase tensors and 3-D inversion are employed to obtain the electrical resistivity model. Our model clearly portrays conductive sedimentary layers beneath the basins with average resistivity of 2.0 Ω·m. The low-resistivity mid-to-lower crust is revealed beneath the Lunpola basin with bulk resistivity of 20 Ω·m and fluid fraction of 1.3-3.0%, which would be attributed to partial melting. Compared to the significant conductive crust in southern Tibet, the crustal rheology is less well developed beneath central Tibet. We propose that the asthenospheric flow beneath central Tibet is responsible for the crustal partial melting and drives the eastward escape of the continental lithosphere in a rigid block fashion.

A document by James Conder. Click on the document to view its contents.

The formation of mineral deposits in mesothermal quartz veins is a complex process that has been the subject of much research. The classical fault-valve hypothesis suggests that mineralization occurs when metamorphic fluids are injected during a brittle event and then locked in to mineralize, but this hypothesis does not fully explain the regular spacing of repeated mineralized patterns that are often observed. This paper proposes a new mechanism for mineralizing systems based on the theory of cnoidal waves in solids. Cnoidal waves are standing waves that can persist for long times in materials under compressive and extensional regimes. We investigate mineral deposits by analytical and numerical methods and show that the cnoidal wave instability theory provides a plausible alternative mechanism for mineralizing systems. This study opens a new avenue for field studies to demonstrate that the mechanism-based cnoidal waves play an essential role in the formation of mineral deposits.

A document by Vishal Mishra. Click on the document to view its contents.

Coral reefs protect coastlines from inundation and flooding, servicing over 200 million people globally. Wave transformation has previously been studied on coral reef flats with limited focus on forereef zones where wave transformation is greatest during high-energy conditions. This study investigates the role of forereef spur and groove (SaG) morphology on wave energy dissipation and overtopping on coral reefs. Using XBeach on LiDAR-derived bathymetry, we reproduced dissipation rates comparable to SaG field studies. Our results emphasize accurate bathymetries’ role in forereef wave energy dissipation models by including morphological features (e.g., groove sinuosity, irregular forereef slopes) that control the mode of wave energy dissipation (frictional and breaking). We then investigated changes to wave energy dissipation and wave overtopping based on IPCC AR5 low and high emission scenarios (RCP2.6 and RCP8.5) and a total disaster scenario (TD) for the year 2100 considering changes to SaG morphology, wave power and relative sea-level rise. For RCP2.6, an increase in wave heights of 0.8 m and an increase in water level of 0.3 m resulted in a two-fold increase in dissipation rates. For RCP8.5 and TD, with no increase in incident wave height, dissipation rates were 29% and 395% lower than RCP2.6. This resulted in increased overtopping at the reef crest by 1.8 m and 2.7 m for RCP8.5 and TD scenarios, respectively, when compared to RCP2.6. Decreased dissipation rates and increased wave overtopping in forecasted climate conditions suggest the need for strategies to promote coral growth to facilitate high dissipation rates in the future.

A significant shift in Earth’s climate characterizes the Neogene, transitioning from a single-ice-sheet planet to the current bipolar configuration. This climate evolution is closely linked to changing ocean currents, but globally-distributed continuous high-resolution sedimentary records are needed to fully capture this interaction. The Ocean Drilling Program (ODP) Site 752, located on Broken Ridge in the Indian Ocean, provides such a Miocene-to-recent archive. We use X-ray fluorescence (XRF) core scanning to build an eccentricity-tuned age-depth model and reconstruct paleoceanographic changes since 23 Ma. We find two intervals of enhanced productivity, during the early and middle Miocene (18.5 – 13.7 Ma) and late Pliocene/early Pleistocene (3 – 1 Ma). We also report a mixed eccentricity-obliquity imprint in the XRF-derived paleoproductivity proxy. In terms of grain size, three coarsening steps occur between 19.2 – 16 Ma, 10.8 – 8 Ma, and since 2.6 Ma. The steps respectively indicate stronger current winnowing in response to vigorous Antarctic Intermediate Water flow over Broken Ridge in the early Miocene, the first transient onset of Tasman Leakage in the Late Miocene, and the intensification of global oceanic circulation at the Plio-Pleistocene transition. High-resolution iron and manganese series provide a detailed Neogene dust record. This study utilized a single hole from an ODP legacy-site. Nevertheless, we managed to provide novel perspectives on past Indian Ocean responses to astronomical forcing. We conclude that Neogene sediments from Broken Ridge harbor the potential for even more comprehensive reconstructions. Realizing this potential necessitates re-drilling of these sedimentary archives utilizing modern drilling strategies.

Changed hydrological regimes, sea-level rise, and accelerated subsidence are all putting river deltas at risk across the globe. Deltas may respond to these stressors through the mechanism of avulsion. Decades of delta avulsion studies have resulted in conflicting hypotheses that avulsion frequency and location are upstream (water and sediment discharge) or downstream (backwater and sea-level rise) controlled. In this study, we use Delft3D morphodynamic simulations to investigate the main controls over delta avulsion. Avulsion timing and location were recorded in six scenarios modelled over a 400-year period with varying alluvial slopes upstream of a delta slope break (1.13x10-4 to 3.04x10-3) within a range representative global deltas. We measure several independent morphometric variables including avulsion length, delta lobe width, channel width at avulsion, delta topset slope and sediment load. Correlating these variables with the avulsion timescales observed in our model shows that avulsion timescale is mostly controlled by sediment load, which in turn is controlled by the alluvial slope upstream of a delta slope break. With higher stream power index in steeper alluvial slopes, more sediment can be carried within a channel, resulting in more frequent avulsions. Our results are consistent with the avulsion timescale derived from an analytical solution, 19 natural deltas and downscaled physical laboratory deltas. These results help mitigate delta avulsion risk by focusing management efforts on variables that primarily control avulsion in a river delta, but also induce further debate over whether sea-level rise may, or may not, trigger more avulsions in river deltas.

A document by ANA CAROLINA FONSECA. Click on the document to view its contents.

Dataset: https://doi.org/10.7910/DVN/T2LESU

We examined data from the American Geophysical Union (AGU), the world’s largest earth and space science society, to characterize cohort demographics of multiple milestones in a biogeoscientists’ career. Geoscientists of color and White women make up a smaller proportion of those participating in activities critical to transitioning from student to professional (submitting manuscripts, getting published, and being asked to review) in comparison to White men. However, gender parity for biogeoscientists appears within reach at earlier career stages, with 37% AGU Biogeosciences members and 41% of Biogeosciences attendees at the Fall Meeting identifying as women in 2020. Unfortunately, data is lacking to make the same assessment for geoscientists of color. A large proportion of manuscripts are submitted by men (73%), many of which have no co-authors that identify as women or non-binary geoscientists, which likely points to inequitable resources and a greater service burden for scientists from historically excluded groups. Further, our communities’ bias of who we suggest as reviewers results in 85% of the reviewer invites going to White geoscientists and 63% going to men. Thus, while representation of diverse communities has improved in some areas, barriers to publishing results in journals not reflecting society: 25% and 22% of manuscripts were led by or included non-White geoscientists, respectively, and fewer than 5% and 7% were led by or included non-White, women geoscientists, respectively. Therefore, in sectors like academia where publishing remains critical for advancement, this process represents a significant obstacle for biogeoscientists not already part of the majority.

Volcanic ash provides information that can help understanding the evolution of volcanic activity during the early stages of a crisis, and possible transitions towards different eruptive styles. Ash consists of particles from a range of origins in the volcanic system and its analysis can be indicative of the processes driving activity. However, classifying ash particles into different types is not straightforward. Diagnostic observations for particle classification are not standardized and vary across samples. Here we explore the use of machine learning (ML) to improve the classification accuracy and reproducibility. We use a curated database of ash particles (VolcAshDB) to optimize and train two ML-based models: an Extreme Gradient Boosting (XGBoost) that uses the measured physical attributes of the particles, from which predictions are interpreted by the SHAP method, and a Vision Transformer (ViT) that classifies binocular, multi-focused, particle images. We find that the XGBoost has an overall classification accuracy of 0.77 (macro F1-score), and specific features of color (hue_mean) and texture (correlation) are the most discriminant between particle types. Classification using the particle images and the ViT is more accurate (macro F1-score of 0.93), with performances across eruptive styles from 0.85 in dome explosion, to 0.95 for phreatic and subplinian events. Notwithstanding the success of the classification algorithms, the used training dataset is limited in number of particles, ranges of eruptive styles, and volcanoes. Thus, the algorithms should be tested further with additional samples, and it is likely that classification for a given volcano is more accurate than between volcanoes.

High fracture density in fault damage zones not only reduces the elastic stiffness of rocks but may also promote time-dependent bulk deformation through the sliding of fracture surfaces and thus impact the stress evolution in fault zones. Comparing the damage zones of the three faults in the Chelungpu fault system encountered in the Taiwan Chelungpu fault Drilling Project (TCDP), the youngest damage zone showed pronounced sonic velocity reduction even though fracture density is the same for all three fault zones, consistent with the shorter healing time of the youngest fault. Caliper log data showed a time-dependent enlargement of the borehole wall at the damage zone. These damage zones record lower differential stress than the surrounding host rock, which cannot be explained by the reduced elastic stiffness in the damage zone. Stress relaxation caused by time-dependent bulk deformation in the damage zone may be responsible for the observed low differential stress.

Quantifying interseismic deformation of fault networks which are predominantly deforming in a north-south direction is challenging, because GNSS networks are usually not dense enough to resolve deformation at the level of individual faults. The alternative, synthetic aperture radar interferometry (InSAR), provides high spatial resolution but is limited by a low sensitivity to N-S motion. We study the active normal fault network of Western Anatolia, which is undergoing rapid N-S extension, using InSAR. In the first part of this study, we develop a workflow to assess the potential of decomposing InSAR line-of-sight (LOS) velocities to determine the N-S component. We use synthetic tests to quantify the impact of noise and other velocity components and outline the requirements to detect N-S deformation in future studies. In its current state, the N-S deformation field is too noisy to allow robust interpretations, hence in the second part we complement the study by including vertical deformation. Since most faults in the study region are normal faults, the high-resolution vertical velocity field provides new insights into regional active faulting. We show that tectonic deformation in the large graben systems is not restricted to the main faults, and seemingly less active or inactive faults could be accommodating strain. We also observe a potential correlation between recent seismicity and active surface deformation. Furthermore, we find that active fault splays causing significant surface deformation can form several kilometres away from the mapped fault trace, and provide an estimate of current activity for many faults in the region.