A document by Jérémie Vasseur. Click on the document to view its contents.

A document by Chaithanya B P. Click on the document to view its contents.

Volcanic meteo-tsunamis, though rare, can pose significant threats to people, as exemplified by the 2022 Hunga Tonga – Hunga Ha’apai (HT-HH) eruption in the SW Pacific. While various studies have delved into the complexities of such phenomena, none have explored analogous scenarios in regions with potential occurrence of large eruptions near or under the sea. We focus on coastal areas along the South China Sea (SCS), among the most densely populated on Earth and historically prone to volcanic activity, including the catastrophic 1883 Krakatau eruption. Here we strategically chose one intra-basin volcano, KW-23612 in the northern SCS, and three extra-basin volcanoes, Banua Wuhu in the Celebes Sea, and Kikai and Fukutoku-Oka-no-Ba in the northern Philippines Sea (southern Japan), from which we simulated volcanic meteo-tsunamis with scaled intensities of the HT-HH event, to assess which countries around the SCS could be more at risk from the occurrence of such phenomena. Our results show that the worst-case scenarios are produced by eruption/tsunamis from the northern SCS, producing offshore waves up to 10 cm offshore Macau and Hong Kong, and up to 20 cm offshore Manila. In contrast, countries bordering the shallow Sunda Shelf (Malaysia, Thailand, Cambodia, and southern Vietnam) seem less at risk from volcanic meteo-tsunamis, though we observed some amplification effects along the deeper Singapore Strait. This study is the first of its kind in the region and sets the basis to investigate amplification effects, and shallow coastal dynamics at key locations, after integrating higher resolution bathymetry data.

The Eocene (55-34 Mya) was marked by a transition from a greenhouse to an icehouse climate, and also experienced several hyperthermals, which are rapid, extreme global warming events. These hyperthermal events were caused by rapid increases in atmospheric CO2 concentration, so they provide the opportunity to study how Earth systems respond to rapid and high magnitude changes in atmospheric CO2. Understanding the drivers of major climate change events, like these ones, is an important step in understanding modern climate change. One such event, the Middle Eocene Climatic Optimum, was a major climatic shift lasting approximately 500 kyr. Orbital forcers, most notably variations in the amount of solar irradiance reaching Earth, are believed to explain many of the observed climatic variations in both this epoch and others. Changes in orbital patterns are widely believed to explain cyclicities on the 20,000 to 100,000 year scale, while changes in solar irradiance have effects on the sub-1,000 year scale. However, little work has been done to understand the influence of orbital cycles of periods between these, in the millennial range. This study aims to bridge this knowledge gap by performing spectral analyses of Middle Eocene Climatic Optimum temperature proxy records to determine if millennial-range orbital cycles have an observable influence on climate dynamics. Using temperature proxy data from four Ocean Drilling Program sites, spectral analysis was performed and prominent signals in the spectra were identified. This analysis showed that all studied sites had a statistically significant signal in the 2500 ± 250-year range, which was identified as the Hallstatt cycle. A suggested mechanism for the Hallstatt cycle, a spin-orbit coupling of the Jovian planets, is astronomical in origin. This adds further evidence that dynamical solar system chaos during this period contributed to the abnormal climate patterns at play and suggests that external factors have a larger climate forcing ability than previously thought. Delving into the intricacies of solar system chaos and its impact on past climates enhances our understanding of present and future climates, thus empowering more accurate and informed predictions going forward.

Using 2D numerical subduction models, we compare deep slab behaviour with oceanic and continental overriding plates and a mantle viscosity structure where the lower mantle viscosity jump occurs either at 660 km or at 1000 km depth as suggested by the latest geoid inversions. We demonstrate that a strong, thick, and buoyant continental plate, combined with a 1000 km depth viscosity increase, promotes slab penetration into the lower mantle. Conversely, the same slab will deflect at 660 km depth if this subducts under an oceanic plate into a mantle where the viscosity increases at the canonical 660 km depth. To quantify these dynamics, we introduce a slab bending ratio, by dividing the deep slab tip angle by the shallow slab angle, reflecting the steepness, and sinking history of the slab. Ocean-ocean convergence models with a viscosity increase coincident with the phase transition at 660 km depth have low ratios and flattened slabs comparable to ocean-ocean cases in nature (e.g., Izu-Bonin). Coupling a continental overriding plate with a 1000 km depth viscosity increase separate from the endothermic phase change results in slabs with high ratio values, and stepped morphologies similar to that observed for the Nazca plate beneath the Southern Peruvian arc. Our results highlight that slab morphologies ultimately express the interaction between the type of overriding plate, slab-induced flow, and phase transitions, modulated by the viscosity structure of the top of the lower mantle and transition zone.

A document by Hamed Amiri. Click on the document to view its contents.

A document by Alamgir Hossan. Click on the document to view its contents.

1. We estimate Walker Lane fault slip rates using a dense filtered and gridded geodetic velocity field and a robust multi-block model approach 2. The geodetic slip rates are independent of geologic slip rates, but 80% agree with them to within uncertainties 3. The method images off-fault deformation and vertical axis rotations providing more insight into how crustal motion drives earthquakes Hammond et al., 2023

Peatlands are fundamental deposits of organic carbon. Thus, their protection is of crucial importance to avoid emissions from their degradation. Peat is a mixture of organic soil that originates from the accumulation of wetland plants under continuous or cyclical anaerobic conditions for long periods. Hence, a precise quantification of peat deposits is extremely important; for that, remote- and proximal-sensing techniques are excellent candidates. Unfortunately, remote-sensing can provide information only on the few shallowest centimeters, whereas peatlands often extend to several meters in depth. In addition, peatlands are usually characterized by difficult (flooded) terrains. So, frequency-domain electromagnetic instruments, as they are compact and contactless, seem to be the ideal solution for the quantitative assessment of the extension and geometry of peatlands. Generally, electromagnetic methods are used to infer the electrical resistivity of the subsurface. In turn, the resistivity distribution can, in principle, be interpreted to infer the morphology of the peatland. Here, to some extent, we show how to shortcut the process and include the expectation and uncertainty regarding the peat resistivity directly into a probabilistic inversion workflow. The present approach allows for retrieving what really matters: the spatial distribution of the probability of peat occurrence, rather than the mere electrical resistivity. To evaluate the efficiency and effectiveness of the proposed probabilistic approach, we compare the outcomes against the more traditional deterministic fully nonlinear (Occam's) inversion and against some boreholes available in the investigated area.  

Southern Alaska is a collage of fault-bounded accreted terranes. The deformation history of these crustal blocks and geometric history of the bounding faults reflect both inherited features and subsequent convergent margin events. Multiple dense (<20-km spacing) arrays of broadband seismometers across southern Alaska has previously allowed for imaging of crustal structure across the region using various seismic imaging methods. Here, we employ S-toP receiver functions to investigate the crustal structure of southern Alaska for signals of dynamic tectonic activity. The subduction zone plate interface and subducting slab Moho are imaged dipping at shallow (<60-km) depths across the southernmost part of the subduction zone. Along two different transects, an inboard-dipping (~15°) boundary is imaged intersecting the trace of the Border Ranges Fault at the surface that we infer represents an unrotated inboard-dipping paleosubduction (Mesozoic) interface. This observation is combined with previous seismic imaging along both the Border Ranges Fault and the next seaward terrane-bounding fault-the Contact Fault-to buttress a known history of convergent tectonics that varies along the margin. Along with large (>10-km) crustal thickness offsets imaged across both the Denali Fault system and the Manuscript in press at upcoming AGU Monograph Tectonics and Seismicity of Alaska and Western Canada: Earthscope and Beyond 2 Eureka Creek Fault, this feature supports a Mesozoic-to-Present inboard-dipping (east and northward) subduction polarity in the region. Additionally, the Sp CCP volume reveals a 100-km x 50-km sized positive velocity gradient with depth (PVG) at ~25-km depth beneath the Copper River Basin, which we interpret as the top of a region of active underplating and/or intrusion of basaltic magmatism into the lower crust. This feature may be related to the generation of a new Wrangell Volcanic Field volcano, resulting from the underlying tear in the subducting slab.

Faulting and folding of basement rocks together accommodate convergence within continental orogens, forming complex zones of intraplate deformation shaped by the fault interaction. Here we use the river terraces along the Dongda river to examine the tectonic deformation patterns of the hinterland and the foreland of the eastern North Qilian Shan, a zone of crustal shortening located at the northeast margin of the Tibetan Plateau. Five Late Pleistocene-Holocene terraces of Dongda river are displaced by three major reverse faults: Minle-Damaying fault, Huangcheng-Ta’erzhuang fault, and Fengle fault, from south to north. Based on displaced terrace treads, we estimated vertical slip rates along the Minle-Damaying fault as 0.7–1.2 mm/a, and along Fengle fault as 0.5–0.7 mm/a. Deformed terraces suggest additional uplift of ~ 0.2 mm/a through folding of the Dahuang Shan anticline. Inhomogeneous uplift of the intermontane basins between the Minle-Damaying fault and the Dahuang Shan anticline indicates a 0.9 ± 0.2 mm/a uplift rate along the Huangcheng-Ta’erzhuang fault. Kinematic modeling of this thrust system shows that deformation propagated northward toward the foreland along a south-dipping 10° décollement rooted into Haiyuan fault at the depth of 20–25 km. This system accommodates 2.7–3.8 mm/a total crustal shortening rate. We suggest this broad thrust belt and the relatively high rate of shortening within this part of the eastern Qilian Shan is as a result of the oblique convergence along a restraining bend of Haiyuan fault system. The elevated shortening rate within this area indicates high potential seismic hazard.

Interaction between large-scale tectonics of the Himalaya and the Indian summer monsoon play a major role in shaping drainage systems of major Himalayan rivers. In this study we attempted to track the sediment sources of the Neogene‒Quaternary fluvial deposits of the Kasauli Formation and Siwalik Group in the Subathu Basin of the Western Himalayan foreland basin. The depositional interval of these deposits spans from middle Miocene to Pliocene which overlap with the onset of Indian monsoon and its influence on the denudation of Himalayan rocks. Provenance analysis based on our detrital zircon U-Pb geochronology and bulk rock Sr-Nd-Hf isotope data indicates that these Neogene‒Quaternary rocks record chiefly the exhumation of the Higher Himalayan Crystalline Sequence. However, at recurrent intervals within the Siwalik Group the presence of zircon population 40–110 Ma in age suggests a sediment sourcing from the Trans Himalayan batholith. We propose that the Sutlej River that originates in south Tibet acted as a transverse paleodispersal system and routed these arc-derived sediments to the Himalayan foreland basin via one of its extinct paleochannels. Zircon data suggest that this across-orogen routing system was particularly effective during the deposition of Middle Siwalik Formation (ca 11- 4.5 Ma), when the rate of uplift of the Himalaya decreased. On the other hand, the small-scale fluctuations in the presence of the Trans Himalayan zircons observed in the Lower and Upper Siwalik formations may primarily reflect climatic forcing, which induced changing monsoon precipitation and the Sutlej’s transport capacity between dry and moist periods.

Topography is a key control on runoff generation, as topographic slope affects hydraulic gradients and curvature affects water flow paths. At the same time, runoff generation shapes topography through erosion, which affects landscape morphology over long timescales. Previous modeling efforts suggest that subsurface hydrological properties, relative to climate, are key mediators of this relationship. Specifically, when subsurface transmissivity and water storage capacity are low, (1) saturated areas and storm runoff should be larger and more variable, and (2) hillslopes shorter and with less relief, assuming other geomorphic factors are held constant. While these patterns appear in simulations, it remains uncertain whether subsurface properties can exert such a strong control on emergent properties in the field. We compared emergent hydrological function and topography in two watersheds that have very similar climatic and geologic history, but very different subsurface properties due to contrasting bedrock lithology. We found that hillslopes were systematically shorter and saturated areas more dynamic at the site with lower transmissivity. To confirm that these differences were due to subsurface hydrology rather than differences in geomorphic process rates, we estimated all parameters of a coupled groundwater-landscape evolution model without calibration. We showed that the difference in subsurface properties has a profound effect on topography and hydrological function that cannot be explained by differences in geomorphic process rates alone. The comparison to field data also exposed model limitations, which we discuss in the context of future efforts to understand the role of hydrology in the long-term evolution of Earth’s critical zone.

Tectonically beheaded valleys represent strain markers that can be used to constrain the geometry and kinematics of dip-slip faults. Quantifying the cumulative deformation they have recorded requires introducing several assumptions that are difficult to test, which limits their practical utility. Here we present a new method which eliminates some of these assumptions by focusing on pairs of beheaded valleys and analyzing them in the chi (horizontal channel coordinate normalized by drainage area) – elevation space. This approach allows tectonic deformation to be retrieved without using any information from the lost upstream catchment, and has therefore the potential of reducing uncertainties associated to the tectonic reconstruction of beheaded valleys. We demonstrate the power of this method by applying it to an outstanding beheaded stream network preserved across the Wadi-al-Akhdar Graben (NW Saudi Arabia). This methodological contribution is expected to revive the use of beheaded valleys by morpho-tectonic studies, and stimulate the exploration of its potential for long-term tectonic reconstructions

Sedimentary mercury (Hg) has become a widely used proxy for paleo-volcanic activity. However, scavenging and drawdown of Hg by organic-matter (OM) and sulfides are important non-volcanic factors determining variability in such records. Most studies, therefore, normalize total Hg (HgT) to a Hg “host-phase” proxy (e.g., HgT/TOC for OM, HgT/TS for sulfides), with the dominant host-phase determined based on the strongest observed (linear) correlations. This approach suffers from various non-linearities in Hg-host-phase behavior and does not account for succession-level, let alone sample-level, Hg speciation changes. Thermal desorption characteristics or ‘profiles’ (TDPs) for many Hg species during pyrolysis analysis are well-established with applications including distinguishing between OM-bound Hg and different Hg sulfides and oxides in (sub-)recent sediments. We explore the use of TDPs for geological sediment (rock) samples and illustrate the presence of multiple release phases (Hg species) – correlated to geochemical host-phase – in (almost) all the 65 analyzed Tithonian (146 – 145 Ma) silt and mudrock samples. By quantifying the Hg in each release phase for every sample, we find TOC concentration may determine ~60% of the variability in the first (lower temperature) Hg TDP release phase: a stark difference with the total Hg released from these samples, where ~20% of variation is explained by TOC variability. TDPs provide insight on sample-level Hg speciation and demonstrate that, while the common assumption of single-phase Hg speciation in sedimentary rocks is problematic, differences in Hg speciation can be detected, quantified, and accounted for using commonly applied techniques - opening potential for routine implementation.

We propose the “endo-exo” conceptual framework to account for the varied and complex episodic landslide movements observed during progressive maturation until collapse/stabilization. This framework captures the interplay between exogenous stressors such as rainfall and endogenous damage/healing processes. The underlying physical picture involves cascades of local triggered mass movements due to fracturing and sliding. We predict four distinct types of episodic landslide dynamics (exogenous/endogenous-subcritical/critical), characterized by power-law relaxations with different exponents, all related to a single parameter ϑ. These predictions are tested on the dataset of the Preonzo landslide, which exhibited multi-year episodic movements prior to a final collapse. All episodic activities can be accounted for within this classification with ϑ≈0.45±0.1, providing strong support for our parsimonious theory. We further show that the final catastrophic failure of this landslide is clearly preceded by an increased frequency of large velocities corresponding to a transition to a supercritical regime with amplifying positive feedbacks.

The variability in spatial resolution of seismic velocity models obtained via tomographic methodologies is attributed to many factors, including inversion strategies, ray path coverage, and data integrity. Integration of such models, with distinct resolutions, is crucial during the refinement of community models, thereby enhancing the precision of ground motion simulations. Toward this goal, we introduce the Probability Graphical Model (PGM), combining velocity models with heterogeneous resolutions and non-uniform data point distributions. The PGM integrates data relations across varying-resolution subdomains, enhancing detail within low-resolution domains by utilizing information and prior knowledge from high-resolution subdomains through a maximum posterior (MAP) problem. Assessment of efficacy, utilizing both 2D and 3D velocity models-consisting of synthetic checkerboard models and a fault zone model from Ridgecrest, CA-demonstrates noteworthy improvements in accuracy, compared to state-of-the-art fusion techniques. Specifically, we find reductions of 30% and 44% in computed travel-time residuals for 2D and 3D models, respectively, as compared to conventional smoothing techniques. Unlike conventional methods, the PGM's adaptive weight selection facilitates preserving and learning details from complex, non-uniform high-resolution models and applies the enhancements to the low-resolution background domain.

The amount and spatial distribution of surface displacement that occurs during an earthquake are critical information to our understanding of the earthquake source and rupture processes. However, the earthquake surface displacement generally occurs over wide regions, includes multiple components affecting the ground surface at different spatial scales, and is challenging to characterize. In this study, we assess the sensitivity of optical imagery and topography datasets of different resolutions to the earthquake surface displacement when using optical image cross-correlation (OIC) techniques. Results show that the average noise in the output displacement maps linearly increases with decreasing image resolution, leading to greater uncertainty in determining the geometry of the faults and the associated displacement. Fault displacements are, on average, under-estimated by a factor ~0.7-0.8 when using 10 m compared to 0.5 m resolution imagery. Our analysis suggests that an optical image resolution of ≤1 m is necessary to accurately capture the complexity of the ground displacement. We also demonstrate that sub-meter vertical accuracy of the digital surface/elevation model (DSM/DEM) is also required for accurate image orthorectification, and is better achieved using high-resolution stereo optical imagery than existing global baseline topography data. Together, these results highlight the measurement needs for improving the observation of earthquake surface displacement towards the development of future Earth surface topography and topography change observing systems.

Present-day convergence between Caribbean and North American plates is accommodated by subduction zones, major active thrusts and strike-slip faults, which are probably the source of the historical large earthquakes on Hispaniola. However, little is known of their geometric and kinematic characteristics, slip rates and seismic activity over time. This information is important to understand the active tectonics in Hispaniola, but it is also crucial to estimate the seismic hazard in the region. Here we show that a relatively constant NE-directed shortening controlled the geometry and kinematics of main active faults in southern central Hispaniola, as well as the evolution of the Quaternary stress regime. This evolution included a pre-Early Pleistocene D1 event of NE-trending compression, which gave rise to the large-scale fold and thrust structure in the Cordillera Central, Peralta Belt, Sierra Martín García and San Juan-Azua basin. This was followed by a near pure strike-slip D2 stress regime, partitioned into the N-S to NE-SW transverse Ocoa-Bonao-La Guácara and Beata Ridge fault zones, as well as subordinate structures in related sub-parallel deformation corridors. Shift to D2 strike-slip deformation was related to indentation of the Beata Ridge in southern Hispaniola from the Early to Middle Pleistocene and continues today. D2 was locally coeval by a more heterogeneous and geographically localized D3 extensional deformation. Defined seismotectonic fault zones divide the region into a set of simplified seismogenic zones as starting point for a seismic hazard modeling. Highest peak ground acceleration values computed in the Ocoa Bay establish a very high seismic hazard.

Unfrozen water content (UWC) is a key parameter affecting a variety of soil physical-mechanical properties and processes in frozen soil systems. However, traditional estimation models suffer limitations due to oversimplified assumptions or limited applicable conditions. Given that, there is a compelling need to explore alternative modeling approaches that leverage machine learning (ML) algorithms, which have shown increasing potential in engineering fields. To this end, this study evaluated and compared six widely known ML algorithms (i.e., three ensemble models: RF, LightGBM and XGBoost; and three non-ensemble models: KNN, SVR and BPNN) for modeling UWC based on collected experimental datasets. These algorithms were optimized and evaluated using a framework combining Bayesian optimization and cross-validation to ensure model stability and generalization. The results demonstrated that the ensemble tree-based methods, particularly LightGBM and XGBoost, achieved the highest predictive accuracy and superior overall performance. On the other hand, the nonensemble methods exhibited poorer generalization abilities. Interestingly, during 10-fold cross-validation, consistent underperformance was observed for a particular fold, possibly stemming from the challenges of the data distribution in that fold after random shuffling. The present study highlights the effectiveness of ensemble learning approaches, importance of proper hyperparameter tuning and validation strategies, and intrinsic modeling challenges arising from the difference between the freezing and thawing phase change behaviors. This comprehensive ML model comparison and robust training framework provide valuable guidance on selecting suitable data-driven techniques for modeling frozen soil properties for cold regions hydrogeology and engineering practices.

A document by Eungyu Park. Click on the document to view its contents.

Thermal runaway is a ductile localization mechanism that has been linked to deep-focus earthquakes and pseudotachylyte formation. In this study, we investigate the dynamics of this process using one-dimensional, numerical models of simple shear deformation. The models employ a visco-elastic rheology where viscous creep is accommodated with a composite rheology encompassing diffusion and dislocation creep as well as low-temperature plasticity. To solve the nonlinear system of differential equations governing this rheology, we utilize the pseudo-transient iterative method in combination with a viscosity regularization to avoid resolution dependencies. To determine the impact of different model parameters on the occurrence of thermal runaway, we perform a parameter sensitivity study consisting of 6000 numerical experiments. We observe two distinct behaviors, namely a stable regime, characterized by transient shear zone formation accompanied by a moderate (100 - 300 Kelvin) temperature increase, and a thermal runaway regime, characterized by strong localization, rapid slip and a temperature surge of thousands of Kelvin. Nondimensional scaling analysis allows us to determine two dimensionless groups that predict model behavior. The ratio tr/td represents the competition between heat generation from stress relaxation and heat loss due to thermal diffusion while the ratio Uel/Uth compares the stored elastic energy to thermal energy in the system. Thermal runaway occurs if tr/td is small and Uel/Uth is large. Our results demonstrate that thermal runaway is a viable mechanism driving fast slip events that are in line with deep-focus earthquakes and pseudotachylyte formation at conditions resembling cores of subducting slabs.

Impact craters that form on every planetary body provide a record of planetary surface evolution. On heavily-cratered surfaces, new craters that form often overlap older craters, but it is unknown how the presence of older craters alters impact crater formation. We use overlapping complex crater pairs on the lunar surface to constrain this process and find that crater rims are systematically lower where they intersect antecedent crater basins. However, the rim morphology of the new crater depends on both the depth of the antecedent crater and the degree of overlap between the two craters. Our observations suggest that transient rim collapse is altered by antecedent topography, leading to circumferential distribution of rim materials in the younger crater. This study represents the first formalization of the influence of antecedent topography on rim morphology and provides process insight into a common impact scenario relevant to the geology of potential Artemis landing sites.

In geological characterization, the traditional methods that rely on the covariance matrix for continuous variable estimation often either neglect or oversimplify the challenge posed by subsurface non-stationarity. This study presents an innovative methodology using ancillary data such as geological insights and geophysical exploration to address this challenge directly, with the goal of accurately delineating the spatial distribution of subsurface petrophysical properties, especially, in large geological fields where non-stationarity is prevalent. This methodology is based on the geodesic distance on an embedded manifold and is complemented by the level-set curve as a key tool for relating the observed geological structures to intrinsic geological non-stationarity. During validation, parameters 𝜌 and 𝛽 were revealed to be the critical parameters that influenced the strength and dependence of the estimated spatial variables on secondary data, respectively. Comparative evaluations showed that our approach performed better than a traditional method (i.e., kriging), particularly, in accurately representing the complex and realistic subsurface structures. The proposed method offers improved accuracy, which is essential for high-stakes applications such as contaminant remediation and underground repository design. This study focused primarily on twodimensional models. There is a need for three-dimensional advancements and evaluations across diverse geological structures. Overall, this research presents novel strategies for estimating non-stationary geologic media, setting the stage for improved exploration of subsurface characterization in the future.