Deep Zone Research Articles

Short-term wave forecasting for offshore wind energy in the Baltic Sea

The increasing interest in ocean-based renewable energy sources and the consequent need for advanced marine infrastructure have heightened the demand for accurate short-term forecasting of significant wave height (SWH). Given the impending investments in offshore infrastructure within the Baltic Sea, it becomes imperative to devise artificial intelligence strategies that can accurately predict wave parameters under the unique conditions of a shallow, tideless sea. This study presents an extensive evaluation of established machine learning techniques tailored to site specific wave spectra. We explore the effectiveness of artificial neural networks (ANNs) in the short-term prediction of SWH. Rigorous optimization of neural network hyperparameters is applied to improve forecast accuracy, with models validated on real-world datasets, proving their ability to predict SWH accurately across various forecast horizons. In addition, the performance of ANNs models is compared to optimized traditional forecasting methods, noting significant improvements in both accuracy and reliability. The results underscore the critical role of careful optimization in achieving precise short-term forecasts at targeted locations. They also suggest that even relatively simple models, when fine-tuned, can surpass the performance of more complex approaches commonly found in the literature. Building upon the foundational advancements in ANNs from the early 2000s, this research adopts a direct forecasting methodology utilizing data from marine observational platforms. Significantly, the networks are trained and validated with data directly obtained from a measurement buoy positioned in a deep water zone, devoid of seabed wave interactions. This aspect is particularly crucial for the strategic placement of future floating offshore farms, where these algorithms will be directly applied for short-term SWH predictions. Our findings underscore the importance of selecting optimal methods to ensure the utmost accuracy of short-term forecasts at targeted locations.

Anatomy of a deep Piedmont critical zone: Evaluating hypotheses on regolith depth controls through comparison of ridge and valley boreholes

AbstractControls on the physical and chemical architecture of the subsurface critical zone are somewhat controversial, with multiple hypotheses proposed to account for variations in the depth of weathering between sites, and with landscape position at a site. In the Piedmont region of the Mid‐Atlantic US weathering of crystalline bedrock has been observed to extend tens of meters below the surface and groundwater in a'bow‐tie’ shape – i.e. weathering extends to lower elevations below ridges than below channels. The chemical and physical structure of a hillslope transect in the Maryland Piedmont was explored with a 45 m borehole in the ridge, as well as shallow bedrock boreholes at the toe of the slope and valley. Chemical weathering fronts were characterized using elemental abundances and mineralogical analysis. The ridge borehole did not extend deeper than the chemically and physically weathered rock. Surface and borehole geophysics and density measurements were used to characterize the weathered rock and saprolite. Na and Ca results suggest that plagioclase feldspar weathering is similar between samples collected from 45 m under the ridge and 2.2 m under the valley bottom. A narrow Fe oxidation garnet weathering front co‐insides with the transition from weathered bedrock to saprolite, suggesting that this reaction may generate initial saprolite porosity. Muscovite weathering co‐occurs with complete depletion of plagioclase a few meters above the Fe oxidation front. These nested weathering fronts in the saprolite appear to follow a subdued version of the surface topography. The location and shape of the nested saprolite weathering fronts may be controlled by the feedback between the transport of reactants and solutes and reaction‐generated porosity, consistent with the conceptual “valve” hypothesis. Differing dominant control mechanisms on deep bedrock weathering and saprolite initiating reactions may explain the thickness and structure of the critical zone at our site.

Combining electrical resistivity tomography and passive seismic to characterise the subsurface architecture of a deeply weathered lateritic hill within the Avon River critical zone observatory

AbstractObserving the subsurface architecture of the deep Critical Zone (CZ), which lies beyond the uppermost layer of accessible soil, is a complex but crucial task. Near‐surface geophysics offers an alternative to accessing the deep CZ at scales relevant to fluid, nutrient and gas transport. As geophysical instruments are sensitive to different subsurface physical properties, their combination can enhance insight into CZ architecture. However, the agreement between and complementarity of multiple geophysical techniques has not been widely assessed for CZ‐related questions. This study employed geophysics to image a highly weathered lateritic hill rich in iron oxides developed from Archean granite within the Avon River Critical Zone Observatory, Western Australia. Data gathered from an electrical resistivity tomography (ERT) and horizontal‐to‐vertical‐spectral‐ratio (HVSR) passive seismic transect were used to visualise CZ architecture through specific resistivity values and ambient noise contrasts. Both techniques revealed a notable degree of lateral variability consistent with the formation of the ~3–4 m thick duricrust‐capped hilltop, the creation of gullies in the sodic material of the pallid zone exposed along the slope and the deposition of ~11 m thick colluvial sediment at the foot slope. Calculated bedrock depth was consistent between the HVSR and ERT instruments along the hilltop plateau but varied from ~23 m to 31 m on the slope and 32 m to 39 m at the foot slope, respectively. Overall, the vertical variation depicted by the ERT, including the differentiation of two layers within the lateritic weathering profile ‐ the pallid zone and saprolite – made up for the inaccuracy of the HVSR technique in depicting layers of similar composition. Moreover, the HVSR method clearly depicted bedrock depth, overcoming the partial masking of the bedrock by saline groundwater in the ERT model. The complementarity of these two methods allowed the development of a detailed conceptual model of subsurface CZ architecture within a saline lateritic weathering profile.

Mantle conduits of the K-Pg Reunion mantle plume rise beneath the Indian subcontinent revealed by 3D magnetotelluric imaging

The central-western region of the Indian subcontinent hosts the vast geological records of its evolution from the Archean to the Recent, including the youngest (∼65 Ma) episode of the Réunion mantle plume activity that produced a large igneous province, the Deccan Volcanic Province (DVP). A three-dimensional lithospheric resistivity image of central-western India is obtained to understand the lithospheric architecture and map any major eruption channels of the Deccan volcanism as no explicit geophysical revelation of such pathways of magma ascend has yet been made. Two high conductivity (< 30 Ωm) pipe-like geometric features originating from a common deep mantle conductive zone under the Malwa plateau (northernmost lobe of the DVP) and its proximity are detected in the resistivity model. These are interpreted to be remnants of the hitherto unknown primary lithospheric pathways of magma ascent from the deep mantle melt-rich zone related to the Reunion mantle plume upwelling under central-western India. This study gives first compelling geophysical evidence of key eruptive centers of the massive Deccan volcanism in central-western India at a locale not anticipated earlier. High to moderate conductivity crustal zones and weak to moderate lithospheric mantle resistivity in most parts of the study region represent an intense and multiphase tectono-magmatic evolution of the region spanning from the Neoproterozoic to the Cretaceous-Paleogene boundary.

Nonlinear Stress-Induced Transformations in Collagen Fibrillar Organization, Disorder and Strain Mechanisms in the Bone-Cartilage Unit.

By developing a 3D X-ray modeling and spatially correlative imaging method for fibrous collagenous tissues, this study provides a comprehensive mapping of nanoscale deformation in the collagen fibril network across the intact bone-cartilage unit (BCU), whose healthy functioning is critical for joint function and preventing degeneration. Extracting the 3D fibril structure from 2D small-angle X-ray scattering before and during physiological compression reveals of dominant deformation modes, including crystallinity transitions, lateral fibril compression, and reorientation, which vary in a coupled, nonlinear, and correlated manner across the cartilage-bone interface. A distinct intermolecular arrangement of collagen molecules, and enhanced molecular-level disorder, is found in the cartilage (sliding) surface region. Just below, fibrils accommodate tissue strain by reorientation, which transitions molecular-level kinking or loss of crystallinity in the deep zone. Crystalline fibrils laterally shrink far more (20×) than they contract, possibly by water loss from between tropocollagen molecules. With the calcified plate acting as an anchor for surrounding tissue, a qualitative switch occurs in fibrillar deformation between the articular cartilage and calcified regions. These findings significantly advance this understanding of the complex, nonlinear ultrastructural dynamics at this critical interface, and opens avenues for developing targeted diagnostic and therapeutic strategies for musculoskeletal disorders.

Depth-wise multiparametric assessment of articular cartilage layers with single-sided NMR.

Articular cartilage (AC) is a specialized connective tissue that covers the ends of long bones and facilitates the load-bearing of joints. It consists of chondrocytes distributed throughout an extracellular matrix and organized into three zones: superficial, middle, and deep. Nuclear magnetic resonance (NMR) techniques can be used to characterize this layered structure. In this study, devoted to a better understanding of the NMR response of this complex tissue, 20 specimens excised from femoral and tibial cartilage of bovine samples were analyzed by the low-field single-sided NMR-MOUSE-PM10. A multiparametric depth-wise analysis was performed to characterize the laminar structure of AC and investigate the origin of the NMR dependence on depth. The depth dependence of the single parameters T1, T2, and D has been described in literature, but their simultaneous measurement has not been fully exploited yet, as well as the extent of their variability. A novel parameter, α, evaluated by applying a double-quantum-like sequence, has been measured. The significant decrease in T1, T2, and D from the middle to the deep zone is consistent with depth-dependent composition and structure changes of the complex matrix of fibers confining and interacting with water. The α parameter appears to be a robust marker of the layered structure with a well-reproducible monotonic trend across the zones. The discrimination of cartilage zones was reinforced by a multivariate principal component analysis statistical analysis. The large number of samples allowed for the identification of the smallest number of parameters or their combination able to classify samples. The first two components clustered the data according to the different zones, highlighting the sensitivity of the NMR parameters to the structural and compositional variations of AC. Using two parameters, the best result was obtained by considering T1 and α. Single-sided NMR devices, portable and low-cost, provide information on NMR parameters related to tissue composition and structure.

Characteristics of rock strength failure and identification of hazardous areas in the roof of deep mining stope

The roof of deep mining stopes is notoriously unstable and challenging to manage due to high in-situ stress and deteriorating rock conditions. To address this issue, a comprehensive approach was employed, incorporating indoor physical experiments, numerical simulations, and field tests to investigate the stope roof rock composition characteristics and strength failure modes in the Laoyingshan deep coal mine. The study revealed the distribution characteristics of the high in-situ stress field in this mining area and delineated different levels of hazards in the roof. The results indicate that, under identical lithological conditions, the mineral composition of deep rock formations is complex. Changes in some mineral components and properties were observed, leading to increased expansiveness and water absorption in clay minerals such as sodium montmorillonite and kaolinite within the basic roof layer. In simulated tests of surrounding rock strength in deep mining stopes, as stress levels approached 2 MPa, the damage factor increased, showing a trend of localized concentration. Internal damage began to exhibit noticeable spatial evolutionary expansion patterns and gradual nucleation. When stress exceeded 8 MPa, rocks transitioned from macroscopic fracture surfaces to microscopic fragmentation zones, with a sudden decrease in stiffness degradation values, internal instantaneous collapse, and phenomena akin to “rock burst” under high stress disturbance. In-situ stress testing determined that the stress field in the deep mining zone of Laoyingshan is in a thrust fault stress state, with horizontal stress predominance. The maximum stress direction is predominantly southwest-northeast, with stress magnitude reaching 25.49 MPa. By arranging post-mining and pre-mining borehole observation stations and utilizing image grayscale fracture recognition technology in MATLAB, the roof was classified into four danger levels: “extremely broken,” “broken,” “significant fractures,” and “minor fractures.” Main control measures for coupling grouting in deep-shallow zonation rigidity were proposed based on these classifications.

Prior3D: An R package for three-dimensional conservation prioritization

Systematic conservation planning (SCP) is essential for meeting global conservation goals and mitigating anthropogenic impacts on biodiversity. Effective conservation planning should incorporate the three-dimensional nature of ecosystems, including species distribution by depth. Recent advancements, like the 3D prioritization approach, address this by considering multiple depth zones. The R package prior3D is an open-source tool designed for prioritizing conservation efforts across different depth zones in a unified framework. Starting from the deepest zone and moving upwards, it optimizes conservation priorities and allows flexible allocation of protection levels per depth. This approach strategically prioritizes areas with higher species gains, while ensuring minimum representation of all depth zones in the final prioritization solution. While conceived for marine conservation, prior3D is applicable to any 3D ecosystem making it a critical tool for multi-realm conservation efforts.

Numerical modeling the process of deep slab dehydration and magmatism

This study uses a 2D high-resolution thermo-mechanical coupled model to investigate the dynamic processes of deep plate hydration, dehydration, and subsequent magmatic activity in ocean-continent subduction zones. We reveal the pathways and temporal evolution of water transport to the deep mantle during the subduction process. Plate dehydration plays a critical role in triggering partial melting of the deep mantle and related magmatic activity. Our study shows significant differences in the volumes of melt produced at different depths, with dehydration reactions in deeper regions being weaker compared to shallower ones. It takes a longer time to reach the suitable P-T conditions for hydrous melting in the deep mantle. The results highlight the geophysical significance of water transport in deep subduction zones and its role in magmatic processes, particularly in the formation of magma chambers beneath continental plates.

Geoelectrical resistivity and geochemistry monitoring of landfill leachates due to the seasonal variations and the implications on groundwater systems and public health

Understanding the seasonal variations in the landfill leachate plumes (LLPs) properties and complex connections between concentrations of leachate variability, and its environment is essential for environmental and public health management. This study explores the combined electrical resistivity (ER) data and physiochemical water analysis (PWA) coupled with the excavations to monitor the landfill physiochemical properties (LPPs) due to seasonal variations and their implications on environmental vital organs and public health. The variations in ER and LLP distributions across the overburdened top layer due to seasonal changes were examined. The low ER contrasts were encountered within the ranges of 1.5 Ωm – 19.0 Ωm which was mapped as LLP accumulated zones within the landfill, while high ER values varied between 15 Ωm – 260 Ωm off-the landfill extending beyond 15 m. The results of the PWA indicate high concentrations of heavy metals (HMs) such as iron (Fe), lead (Pb), zinc (Zn), and cadmium (Cd) decreasing with wet seasons and increasing with dry seasons. The overall high concentration of HMs in the LLPs was indeed varied between 9.81 ± 2.15–19.07 ± 3.68, while the electrical conductivity (EC) significantly increased from 17.99 ± 1.92 mg/L to 24.87 ± 3.31 mg/L towards the wet season. The increment and decrement encountered in the LPPs are due to seasonal variation and dilution. The order of decrement in the HMs in the LLPs treads as follows EC > Fe > Zn > Pb > Cd in values, respectively. The near-surface EC aligned well with the ER results and boundaries of the waste disposal site, which was verified by the soil excavations. In addition, the ER method was extended beyond the landfill for adequate monitoring, identifying the subsurface layers, conductive shallow zones mapped as the zones of LLP accumulation, resistive deep and shallow zones mapped as the consolidated lateritic topsoil and crystalline basement rocks in some cases, and a dipping conductive lineament zones identified as fracture zones just before the crystalline basement. In conclusion, the ER technique reveals the vertical and horizontal extents of the LLP escapade, the PWA expressed the concentrations of HMs in the LLPs, heightening the implications on the environmental and human health. Finally, the combined techniques deployed for monitoring the physiochemical properties of LLPs due to seasonal variation and the impacts on the integrity of groundwater quality systems and public health inform sustainable waste management practices, which contributes significantly to the protection of groundwater resources and the development of effective strategies to safeguard groundwater systems and public health for present and future generations.

Convective Magnetic Flux Emergence Simulations from the Deep Solar Interior to the Photosphere: Comprehensive Study of Flux Tube Twist

The emergence of magnetic flux from the deep convection zone plays an important role in solar magnetism, such as the generation of active regions and triggering of various eruptive phenomena, including jets, flares, and coronal mass ejections. To investigate the effects of magnetic twist on flux emergence, we performed numerical simulations of flux tube emergence using the radiative magnetohydrodynamic code R2D2 and conducted a systematic survey on the initial twist. Specifically, we varied the twist of the initial tube both positively and negatively from zero to twice the critical value for kink instability. As a result, regardless of the initial twist, the flux tube was lifted by the convective upflow and reached the photosphere to create sunspots. However, when the twist was too weak, the photospheric flux was quickly diffused and not retained long as coherent sunspots. The degree of magnetic twist measured in the photosphere conserved the original twist relatively well and was comparable to actual solar observations. Even in the untwisted case, a finite amount of magnetic helicity was injected into the upper atmosphere because the background turbulence added helicity. However, when the initial twist exceeded the critical value for kink instability, the magnetic helicity normalized by the total magnetic flux was found to be unreasonably larger than the observations, indicating that the kink instability of the emerging flux tube may not be a likely scenario for the formation of flare-productive active regions.

Assessing Nitrate Leaching During Drought and Extreme Precipitation: Exploring Deep Vadose‐Zone Monitoring, Groundwater Observations, and Field Mass Balance

AbstractThe increasing concern over agricultural practices' impact on groundwater quality necessitates comprehensive studies to evaluate and compare monitoring strategies for nitrate leaching. This work addresses this imperative by examining three methodologies: deep vadose‐zone monitoring, shallow groundwater intensive monitoring, and field‐level mass balance. The primary objective of the study was to assess nitrate leaching from an intensively cropped processing tomato rotation field using three different methods. Additionally, this study focuses on contrasting conditions between the growing season (characterized by drought in some years) and the winter/rainy season (characterized by extreme precipitation in some years). Results indicate varying degrees of nitrate leaching across methods, with all approaches detecting leaching events during the growing season and off‐season precipitation. Despite uncertainties inherent in field‐level mass balance estimates, they align reasonably with intensive in‐situ monitoring results using the deep Vadose Monitoring System (VMS). Throughout two growing seasons and corresponding fall‐winter rainy periods, the VMS effectively tracked seasonal nitrogen leaching below the root zone, correlating with observed groundwater nitrate concentrations increases following extreme precipitation events. Nitrate leaching increased during heavy rainfall in the winter following dry summer periods observed across the deep vadose zone using two VMS systems. This underscores the importance of continuous monitoring and assessment in understanding nitrate dynamics and groundwater contamination risks. In conclusion, this study contributes to knowledge and ongoing research by providing insights into effective monitoring strategies for nitrate leaching into groundwater from intensive cropping systems.

Investigating the role of groundwater in ecosystem water use efficiency in India considering irrigation, climate and land use

Terrestrial ecosystems (TEs) play a crucial role in carbon sequestration and climate regulation. While interactions between surface water and ecosystems are well-studied, groundwater-ecosystem relationships remain poorly understood, particularly in groundwater-dependent regions like India. This study investigates the relationship between water table depth (WTD) and ecosystem productivity across India, considering the variation in irrigation practices, land use and climate types, from 2000 to 2021. We employ Ecosystem Water Use Efficiency (WUEe), the rate of carbon uptake per unit of water consumed, to examine these interactions at different spatial scales. Our findings reveal a strong link between WUEe and WTD. Shallower WTD regions, such as the lower Himalayas and Northeast India with forests and dominated by a wet/humid subtropical climate, exhibit higher WUEe (1.5–3.5 g C/kg H2O). Whereas deeper WTD regions like northwest India, characterized by shrublands and an arid climate, display lower WUEe (<1 g C/kg H2O). This suggests vegetation in arid/semi-arid regions shows higher sensitivity to water availability compared to wetter areas. This is also evident by a declining WUEe trend and increasing elasticity of WUEe (εWUE) to interannual climatic variability with increasing WTD in these regions. Furthermore, the study identifies potential unsustainable groundwater use for irrigation in areas like the Trans Gangetic plains. Irrigation has a strong correlation with evapotranspiration (ET) (r = 0.4–0.6) in deep WTD zones, but no correlation with WUEe. This implies that intense and unsustainable irrigation might disrupt the natural water use strategies of vegetation. This research, by improving understanding of these interactions, aims to contribute to the sustainable management of India's groundwater resources.

Structural and hydrodynamic modelling of the probability of breakage of branching and plate coral colonies

Climate change is amplifying the intensity of severe weather events, with coastal regions such as coral reefs facing heightened vulnerability to cyclonic wave forces. Structural models to predict bending stress and breakage of corals have been developed for coral colonies to enhance comprehension and prediction of the effects of hydrodynamic disturbances on coral reefs. However, there is scope for improving these predictions by evolving the methodology for quantifying complicated and variable coral morphologies. This study aims to predict breakage thresholds for two of the most prevalent coral morphologies: branching and plate corals (using Acropora muricata and Acropora hyacinthus as study species). Laboratory and field measurements were taken to assess coral morphologies and material characteristics. Morphological features of 47 branching colonies and 100 plate colonies were surveyed at the study site (Heron Reef, southern GBR) and the tensile strength of 80 coral samples was obtained by in situ and laboratory testing. Three-dimensional structural models of branching and plate coral colonies were developed, encompassing multiple coral colonies with varying morphological patterns from relatively shallow (5–7 m) to deep (9–12 m) zones. Model results were calibrated and verified with existing data, revealing that velocity thresholds of 1.7 m/s and 5.0 m/s would destroy 90% of the simulated branching coral structures growing in the deep and shallow parts of the forereef zone, respectively. In contrast, the plate corals have sufficient margins of safety even in extreme flow conditions (7 m/s). Additionally, skeletal strength and structural performance were adjusted based on varying degrees of bioerosion inside the coral skeleton. A higher probability of breakage was observed as the extent of bioerosion increased. The laboratory experiments of hydrodynamic loads on coral colony show that the sheltering effect due to one or two neighbouring colonies in the upwave direction is negligible. These models can be easily adjusted to provide predictions for other coral species, shapes, levels of bioerosion, and locations (e.g., sheltered or exposed areas). Comprehensive predictions about the level of expected damage and rubble generation in different areas can be used in reef management planning and restoration prioritization.

Geophysical characterization of the bedrock and regolith in the Pranmati basin critical zone, Uttarakhand Himalaya

The young active Himalayan mountain is characterized by steep slope and dissected topography in overall compressive tectonic setting. The mountain belt has primarily coarse textured soil with poor water holding capacity and is highly prone to erosion. The erosion not only affects many ecosystems located at downstream but also has detrimental effects on the critical zone (CZ). In the present study, we have carried out DC electrical resistivity study in the Pranmati catchment of the Alaknanda basin, a Himalayan critical zone in the Lesser Himalaya, to understand the pattern of soil erosion, transportation and deposition by characterizing the bedrock architecture and hence regolith thickness. A total of 6 electrical resistivity tomogram (ERT) profiles were laid at two locations in the catchment, one in a plain grassland and another at a crop field located on a hill slope of >25o. The study area in the Baijnath klippe, consists of quartz-biotite gneisses with layers of quartz mica-schist enclosed by thrust faults. Electrical resistivity sections of the downslope grassland site show a sharp resistivity contrast between the southwest and northeast transects suggesting south-eastern increase in dip of the bedrock, oblique to the north-east facing surface topography and a thick regolith (> 10 m). The resistivity sections of the site located on the hillslope yield a very thin layer of regolith (< 2 m) indicating significant soil erosion and high weathering of the bedrock. We propose that the water–rock interaction within the porous regolith facilitated by subsurface water circulation might be a potential source for the thick regolith. The observations substantiate existing hypotheses for the evolution and development of deep critical zones. From the results, it has been hypothesized that the bedrock architecture and water channel paths within the CZ together control the regolith thickness.

Detection of Hidden Low-Frequency Earthquakes in Southern Vancouver Island with Deep Learning

Low-frequency earthquakes (LFEs) are small-magnitude earthquakes that are depleted in high-frequency content relative to traditional earthquakes of the same magnitude. These events occur in conjunction with slow slip events (SSEs) and can be used to infer the space and time evolution of SSEs. However, because LFEs have weak signals, and the methods used to identify them are computationally expensive, LFEs are not routinely cataloged in most places. Here, we develop a deep-learning model that learns from an existing LFE catalog to detect LFEs in 14 years of continuous waveform data in southern Vancouver Island. The result shows significant increases in detection rates at individual stations. We associate the detections and locate them using a grid search approach in a 3D regional velocity model, resulting in over 1 million LFEs during the performing period. Our resulting catalog is consistent with a widely used tremor catalog during periods of large-magnitude SSEs. However, there are time periods where it registers far more LFEs than the tremor catalog. We highlight a 16-day period in May 2010, when our model detects nearly 3,000 LFEs, whereas the tremor catalog contains only one tremor detection in the same region. This suggests the possibility of hidden small-magnitude SSEs that are undetected by current approaches. Our approach improves the temporal and spatial resolution of the LFE activities and provides new opportunities to understand deep subduction zone processes in this region.

Fault zone architecture and hydraulic properties characterization using earth tide analysis

Fault zone architecture and hydraulic properties, which determine subsurface fluid flow and storage, have received long-term research attention from hydrogeologists. Current field experimental techniques and numerical simulation methods are limited by the scale and complexity of the investigations and are inadequate for deep subsurface fault zones. Estimating the internal rock properties and structures of fracture zones requires a combination of methods from many different fields. In recent years, groundwater tidal response methods have been widely used to characterize subsurface hydrogeomechanical properties because of their advantages of being in situ and low cost. In this study, tidal analysis was employed for a well within the Blue Ridge Fault Zone, and we integrated the fracture zone properties revealed by a single well. Well W-03 revealed an aquifer with an overall permeability of ∼ 10–14 m2 and hydraulic diffusivity of 0.24 m2⋅s−1. The fault damage zone had a permeability of 10–14 ∼ 10–13 m2 while the host rock had a permeability of 10–16 ∼ 10–14 m2. In addition, we found that the heterogeneity of specific storage affects the assessment of poroelasticity parameters, we offer a method to estimate these parameters without relying on specific storage, yielding porosity estimates ranging from 0.05 to 0.06, aligning with field test results. Furthermore, the estimated dip and strike of the fault zone were also consistent with the outcrop and borehole observations.

Locating Boundaries Between Locked and Creeping Regions at Nankai and Cascadia Subduction Zones

AbstractInterseismic coupling maps and, especially, estimates of the location of the fully coupled (locked) zone relative to the trench, coastline, and slow slip events are crucial for determining megathrust earthquake hazard at subduction zones. We present an interseismic coupling inversion that estimates the locations of the upper and lower boundaries of the locked zone, the lower boundary of the deep transition zone, and downdip gradient of creep rate in the transition from locked to freely creeping in the downdip transition zone. We show that the locked zone at Cascadia is west of the coastline and 10 km updip of the slow slip zone along much of the margin, widest (25–125 km, extending to ∼19 km depth) in northern Cascadia, narrowest (0–70 km) in central Cascadia, with moment accumulation rate equivalent to a Mw 8.71 and Mw 8.85 earthquake for 300‐ and 500‐year earthquake cycles. We find a steep gradient in creep immediately below the locked zone, indicative of propagating creep, along the entire margin. At Nankai, we find three distinct zones of locking (offshore Shikoku, offshore southeast Kii peninsula, and offshore Shima peninsula) with a total moment accumulation rate equivalent to a Mw 8.70 earthquake for a 150‐year earthquake cycle. The bottom of the locked zone is nearly under the coastline for all three locked regions at Nankai and is positioned 0–5 km updip of the slow slip zone. In contrast with Cascadia, creep rate gradients below the locked zone at Nankai are generally gradual, consistent with stationary locking.

Multi‐Stage Magmatism During Slab Exhumation Drives the Geochemical Evolution of Continental Crust: Insights From Paleozoic Granitoids in South Altyn, Western China

AbstractThe present continental crust is characterized by a felsic upper crust and a mafic lower crust, resulting from significant geochemical differentiation over geological time. While various processes have been proposed to explain this differentiation, subduction zones remain pivotal regions for understanding the compositional evolution of continental crust. This study focuses on the South Altyn (SA) continental subduction‐collision belt in western China, a unique setting that experienced ultra‐deep (&gt;300 km) continental subduction followed by multi‐stage exhumation. We present a comprehensive study of four granitoid suites from Tatelekebulake (TTLK) area in SA: biotite granite (BG), monzogranite (MG), K‐feldspar granite (KG), and leucogranite (LG). Comprehensive studies on petrology, geochemistry and zircon U‐Pb dating show that these granitoids formed at 494, 451, 414, and 418 Ma, respectively, and originated from protoliths with affinity to the subducted continental crust in SA. Phase equilibrium modeling suggests that BG formed at ∼800°C and 0.6 GPa, while the MG, KG, and LG formed by differentiation crystallization of the BG magma under progressively decreasing temperature and pressure conditions (750°C, 0.5 GPa; 740–700°C, 0.2 GPa; and 700–640°C, 0.1 GPa, respectively). These results, combined with previous studies, allow us to reconstruct the tectonic processes of continental exhumation and subsequent orogenic collapse in SA during the Early Paleozoic. Importantly, our findings reveal that magmatism derived from partial melting of subducted continental crust can promote the geochemical evolution of continental crust toward more felsic compositions, even in the absence of significant crustal growth or mantle‐derived magmatism. This study provides a valuable case for understanding the compositional evolution of continental crust in deep subduction zones and challenges conventional models that rely heavily on arc magmatism for crustal differentiation. Moreover, our results contribute to a broader understanding of crustal evolution processes in collisional orogens worldwide and highlight the importance of recycling and differentiation of subducted continental material in shaping crustal compositions.

Mesoscale cyclonic eddies born in an eastern boundary upwelling system enhance microbial eukaryote diversity in oligotrophic offshore waters

Mesoscale eddies which originate in Eastern Boundary Upwelling Systems (EBUS) such as the Canary Current System, entrap nutrient-rich coastal water and travel offshore while aging. We have analyzed the protistan plankton community structures in the deep chlorophyll maximum (DCM), sub-DCM, and oxygen minimum zone (OMZ) of three differently aged cyclonic EBUS eddies off Northwest Africa, as well as of non-eddy affected reference sites, using DNA metabarcoding. Throughout all water depths, we found that the investigated eddies generated local dispersal-driven hotspots of protistan plankton diversity in the naturally oligotrophic subtropical offshore waters off Northwest Africa. Based on the taxonomic composition of protistan plankton communities, these diversity hotspots are likely to play an important role in carbon sequestration and for regional food webs up to top predatory levels. Thereby, the life-span of an eddy emerged as an important criterion, how local offshore protistan plankton diversity is transformed quantitatively and qualitatively: each of the three eddies was characterized by notably distinct protistan plankton communities. This could be linked to the physicochemical water properties (predominantly macronutrients, temperature, and salinity) of the eddies' cores and rings, which experience pronounced changes during the eddies’ westward trajectories. Furthermore, we found evidence that eddy-specific deep-water protistan communities are relatively short-lived compared to the ones in the sunlit DCM. However, our results do not only witness from the importance of fine-scale physical ocean features for regional ecosystem processes, but they also show the complexity of these ocean features and that we are still far from understanding the biological processes and their driving forces in such features.