Off-fault deformation feedback and strain localization precursor during laboratory earthquakes.

Recent large-scale seismological observations have shown that off-fault strain localization and foreshock migration could serve as an early warning of an impending earthquake. However, this process is still largely unknown. In this study, state-of-the-art friction experiments were conducted in a oil-confined biaxial shear apparatus to investigate the link between stick-slip nucleation and off-fault deformation. Our findings indicate that there is a direct link between stick-slip nucleation and off-fault deformation, provided that the fault is conditionally unstable (a - b < 0). Inelastic off-fault deformation may trigger unstable slip by decreasing the stiffness of the surrounding rock volume, which favors earthquake nucleation. Additionally, the study presents laboratory observation of precursory strain localization around a fault during stick-slip cycles. These findings suggest that volumetric deformation processes could be a main factor in the nucleation of large ruptures and strain localization could be a reliable harbinger of large earthquakes.

A common precursor for global hotspot lavas.

Hotspot lavas exhibit chemical heterogeneity, much of which is ascribed to heterogeneous deep mantle sources that contain various components with distinct composition, origin and age. However, characterizing primary melt compositions and mantle heterogeneity directly is challenging. Here we investigate a global dataset of hotspot lavas to constrain the incompatible-element composition of their parental melts and sources. Trace-element ratios indicate that the compositional heterogeneity of global hotspot lavas is not primary, but reflects processes that hotspot melts undergo as they ascend to the surface. We find the parental melts of these lavas, as well as of kimberlites and basalts from large igneous provinces, to be uniform in their elemental, and radiogenic and noble-gas isotope, composition. We suggest that the parental melts to all of these lavas derive from a depleted and outgassed mantle reservoir that was replenished with incompatible element-enriched material during the Archaean. This interpretation explains the elemental, radiogenic and noble-gas isotope compositions of hotspot lavas without requiring a heterogeneous lower mantle or the long-term survival of undegassed relics from a primordial Earth.

A national-scale high-resolution CCUS-shared pipeline layout for retrofitting multisectoral plants via onshore-offshore geological storage.

Carbon capture utilization and storage (CCUS) is an indispensable process to mitigate climate change. However, a precise and feasible CCUS layout with realistic geospatial connectivity is essential to support the prospective deployment of multisectoral plants on a national scale. This study proposed an onshore-offshore CCUS source-sink matching model, distinguished by CO2 source-sink dataset enhancement, realistic pipeline network optimization, and onshore-offshore geospatial connectivity to accurately map China's high-resolution CCUS layout. The findings showed that China's multisectoral CCUS supply potential of coal-fired power, steel, cement, and coal chemicals was approximately 1.75, 0.77, 0.56, and 0.23 Gt/a CO2, respectively. A complete geospatial connectivity pattern was established by connecting 1186 multisectoral CO2 sources with 307 onshore and 22 offshore storage sites via the shared pipeline network of 80,700 km, involving plant-level cost heterogeneity, industry competition, and CCUS cluster identification. This model can be applied to other countries or globally to enhance CCUS layout strategies.

The fossil vertebrate primary type specimens in the collection of the University of Otago Department of Geology.

The 47 vertebrate type specimens held in the University of Otago Geology Department are catalogued in detail. A short history of the collection is followed by lists of the type specimens under the Classes Actinopterygii, Reptilia, Aves and Mammalia. A fish trace-fossil is included at the end of the Actinopterygii. Where appropriate, the name changes of the genus or species are given in chronological order. The specimens are briefly described, locality and geological age information is provided.

Automated determination of transport and depositional environments in sand and sandstones.

As sand moves across Earth's landscapes, the shapes of individual grains evolve, and microscopic textures accumulate on their surfaces. Because transport processes vary between environments, the shape and suite of microtextures etched on sand grains provide insights into their transport histories. For example, previous efforts to link microtextures to transport environments have demonstrated that they can provide important information about the depositional environments of rocks with few other indicators. However, such analyses rely on 1) subjective human description of microtextures, which can yield biased, error-prone results; 2) nonstandard lists of microtextures; and 3) relatively large sample sizes (>20 grains) to obtain reliable results, the manual documentation of which is extremely labor intensive. These drawbacks have hindered broad adoption of the technique. We address these limitations by developing a deep neural network model, SandAI, that classifies scanning electron microscope images of modern sand grains by transport environment with high accuracy. The SandAI model was developed using images of sand grains from modern environments around the globe. Training data encompass the four most common terrestrial environments: fluvial, eolian, glacial, and beach. We validate the model on quartz grains from modern sites unknown to it, and Jurassic-Pliocene sandstones of known depositional environments. Next, the model is applied to two samples of the Cryogenian Bråvika Member (of contested origin), yielding insights into periglacial systems associated with Snowball Earth. Our results demonstrate the robustness and versatility of the model in quickly and automatically constraining the transport histories recorded in individual grains of quartz sand.

Validating the application of cyclic hydraulic pressure pulses to reduce breakdown pressure in granite.

As the geoenergy sector moves toward more sustainable practices, an emerging field of research is the proposed utilization of cyclic hydraulic pressure pulses to safely and efficiently enhance productivity. We demonstrate how cyclic hydraulic pressure pulses can reduce hydraulic breakdown pressure in granite using newly developed experimental equipment, which applies pulsed square waves of fluid pressure to large bench-top samples, monitored with dynamic high-resolution fiber optic strain sensors. Our results show a significant reduction in breakdown pressure can be achieved by cyclic pulsed pumping, and we explore the role of mean pressure and cyclic amplitude. Our results offer new insight into cyclic well-stimulation treatments and show potential for reducing peak power consumption during geothermal exploitation.

Effects of mechanical properties of the underburden on induced seismicity along a basement fault during hydrogen storage in a depleted reservoir.

This study models the geomechanical deformation of a depleted gas field, wherein gaseous hydrogen is stored in a North Sea reservoir, and is cyclically injected and withdrawn. A fault is modeled within the underburden, and its slip is investigated during a three year storage period. Parametric simulations are conducted to study the influence of the underburden mechanical properties, such as Young's modulus, Poisson's ratio, and permeability on induced seismicity. The fault is predominantly in stick during the bulk of the injection, storage, and withdrawal periods, but minor fault slip ( < 4 mm) occurs shortly after a change in operational regime. The Young's modulus of the underburden unit has the strongest control on fault slip. To reduce the seismic hazard, an underburden with low Young's modulus ( < 15 GPa), high Poisson's ratio ( > 0.25), low Biot coefficient, and low permeability ( < 1 × 10 - 19 m2) is found to be most suitable for hydrogen storage.

Use of Mohr diagrams to predict fracturing in rock masses, with applications for predicting sub-surface behavior.

Mohr diagrams are a simple and effective method that can help geoscientists consider, model, and predict the ranges of mechanical properties of rock, stresses, fluid pressures, and the resultant fractures that are likely to occur in the sub-surface. Mohr diagrams can be used to make predictions about how rocks may respond to change, with a transition from a stable state to fracturing occurring if there are changes in (1) the failure envelope, (2) stresses, and/or (3) fluid pressure. This article uses Mohr diagrams to address two questions of significance to the energy transition. First, how will metasedimentary rocks, which are potential geothermal reservoir rocks, respond to thermal stimulation? Second, will fractures that may influence the underground storage of radioactive waste develop in a clay sequence during exhumation? Mohr diagrams are shown to be useful for highlighting misconceptions and input data problems, leading to improved understanding of how structures develop.

Rethinking geological concepts in the age of plastic pollution.

This paper attempts to reevaluate traditional geological classifications from sedimentology to stratigraphy as well as the concept of the Holocene/Anthropocene epochs, characterized by the widespread integration of plastics into sedimentary environments. This paper presents a set of novel insights into the interactions between synthetic materials and natural geological processes. We illustrate how plastics not only disrupt sedimentary dynamics and alter the composition of rocks and soils, creating new forms of pollution and also pose escalated threats to marine biodiversity through altered erosion, transport, and deposition patterns. We highlight the emerging role of plastics as distinctive stratigraphic markers, providing a different perspective on human environmental impacts. This analysis challenges the traditional perception of rocks as solely natural, inorganic formations and highlights the critical need for interdisciplinary approaches that meld geology, chemistry, and environmental science. The document calls for intensified research to develop effective strategies for managing these impacts and promotes innovative conservation techniques that address both the symptoms and sources of plastic pollution.

Characterization of the Surfaces and Near-Surface Atmospheres of Ganymede, Europa and Callisto by JUICE.

We present the state of the art on the study of surfaces and tenuous atmospheres of the icy Galilean satellites Ganymede, Europa and Callisto, from past and ongoing space exploration conducted with several spacecraft to recent telescopic observations, and we show how the ESA JUICE mission plans to explore these surfaces and atmospheres in detail with its scientific payload. The surface geology of the moons is the main evidence of their evolution and reflects the internal heating provided by tidal interactions. Surface composition is the result of endogenous and exogenous processes, with the former providing valuable information about the potential composition of shallow subsurface liquid pockets, possibly connected to deeper oceans. Finally, the icy Galilean moons have tenuous atmospheres that arise from charged particle sputtering affecting their surfaces. In the case of Europa, plumes of water vapour have also been reported, whose phenomenology at present is poorly understood and requires future close exploration. In the three main sections of the article, we discuss these topics, highlighting the key scientific objectives and investigations to be achieved by JUICE. Based on a recent predicted trajectory, we also show potential coverage maps and other examples of reference measurements. The scientific discussion and observation planning presented here are the outcome of the JUICE Working Group 2 (WG2): "Surfaces and Near-surface Exospheres of the Satellites, dust and rings".