Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

Green or renewable energy has become vital in achieving net zero carbon and the key enabling technology to realise green energy ambitions is energy storage infrastructure. For instance, power systems in which more than 80% of the supply is generated from renewable sources cannot be balanced using existing storage. In the UK, wind curtailment payments almost doubled in 2020 to a total of £299M and hit a record high of £507M in 2021. The energy wasted in 2020 and 2021 is enough to power 800,000 British homes. Amongst all energy storage means, underground hydrogen storage has shown great potential for large-scale and long-term storage while securing a continuous and well-defined supply stream. Underground hydrogen storage works by injecting hydrogen that is produced from renewable electricity, e.g., wind turbines, into underground geological formations, including depleted oil and gas reservoirs, salt caverns, aquifers and hard rock caverns. The stored hydrogen can then be used for power generation to balance the fluctuation in energy use as well as for fuel to meet transportation demands. Rock caverns are often regarded as the best option for underground hydrogen storage due to their low gas permeability which contributes to excellent sealing strength and capability. Once lined with concrete and a layer of gas-tight material such as stainless steel, PE or PVC, rock caverns can have excellent storage capability for high-density hydrogen with minimum environmental impact. However, the caverns' long-term structural stability and serviceability depend on their material heterogeneity and complex geometries, and the in-situ stress state. The injection and withdrawal process will generate cyclic pressure on the rock mass; as a result, the surrounding rock is subjected to cyclic tensile stress in the tangential direction, possibly together with cyclic shear stress. The cyclic tensile and shear stresses will generate fatigue of rock, i.e., strength reduction, leading to mode-I, mode-II and/or the mixed mode cracks, at (possibly much) lower level of operational pressure. This poses a great threat to the structural integrity and safety of the storage site. In this international partnership project, we aim to address how the in-situ rock is fatigued and fractured under the cyclic pressure that will be generated from the injection and withdrawal of hydrogen, and how rock fatigue may affect the integrity and safety of the hydrogen storage infrastructure. Considering the hydrogen storage working conditions, the research problem can be summarized into low-cycle rock fatigue fracture under high in-situ stress level. Moreover, material heterogeneity, stress state, complex geometries, material creep, etc. can all have effects on the fatigue behavior of rock. To ensure the safe long-term storage of hydrogen in rock caverns it is therefore critically important to have a thorough understanding of rock fatigue mechanisms.

Subduction is one of the main components of the Earth's plate-tectonic engine. Where two plates converge, the coolest and densest plate will slide below the other and sink into the underlying viscous mantle, taking with it basaltic ocean crust, sediments and fluids. The recycling of fluids and sediments lies at the root of the Earth's most explosive volcanism, and is crucial in the formation of continental crust, and production and concentration of ores. Subduction also produces the world's largest earthquakes. However, while in some zones the two plates appear strongly coupled and motions give rise to mega earthquakes, others converge without shaking. Plate coupling may also determine why along some subduction zones, mountain belts like the Andes and Rockies formed, while behind others, new oceans, like the Philippine Sea and Fiji Basin opened. Volcanic arc positions are controlled by how steeply the plate descends into the mantle. The shape of the downgoing plate in the mantle also affects how easily it can sink into the deep mantle. In spite of the importance of these subduction characteristics, at present, we do not understand what forces govern plate coupling, subducting plate shape or subduction motions. The gravitational pull from the dense sinking plates is generally considered to be the dominant driving force of plate tectonics. However, neither observed motions at subduction zones, nor downgoing plate shape, nor upper plate deformation correlate with the density of the downgoing plate. It has been proposed that forcing by the overriding plate or the strength of the downgoing plate can overrule the effects of downgoing plate density. However, we recently developed a two-dimensional model of purely density driven subduction, which demonstrated that the expressions of downgoing plate density can be counterintuitive. For example, we find that young light plates can subduct faster than old dense plates and what is more they often do (Goes et al., Nature 2008). This discovery illustrates our lack of understanding of subduction forces. Here we propose a comprehensive investigation that combines numerical modelling with observations, to explore how three-dimensional variation in downgoing plate density and strength determines subduction behaviour. In the first part of the project, we will systematically document the sensitivity of plate motions and downgoing plate shape to spatial and temporal variations in plate structure. In the second part, we will run a set of models for the Pacific 'Ring of Fire', location of the world's largest subduction zones. Our models of Pacific subduction will be driven by densities from the best-constrained history of plate ages. Where our modelled subduction behaviour is consistent with observed present-day downgoing plate shape, and the history of plate motions, downgoing plate density exerts the dominant control; elsewhere, additional forces must play a role.

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.