In subduction zones, the accretionary wedges play a vital role in mediating the burial processes of incoming oceanic sediments and eventually their return pathways to the surface. A direction of the previous tectonic models invoked the standard corner flow theory, assuming a slab-parallel shear and a rigid, fixed overriding plate, to elucidate the crustal recycling processes in tectonic wedges. To deal with more complex subduction-collisional settings, where they have deformable overriding plates, and associate a horizontal slab migration (advance or rollback) component during subduction, we develop a generalized corner flow model to revisit the problem of return flow mechanics, providing a criticality analysis of the return flows as a function of the geometric, kinematic, and rheological conditions in accretionary wedges. A new set of analytical solutions is presented to evaluate the limiting conditions in which a wedge can set in significant return flows, leading to focused exhumation of the deep-crustal materials. The theoretical results suggest that, for moderate wedge-taper angles (∼30°), the viscosity ratios (μ_r) between the overriding plate and the wedge $\&\#8805;\&\#8764;{\mathrm{10}}^{\mathrm{3}}$μ_r, or addition of slab roll back weakens the return flows, whereas slab advance greatly strengthens the return flows. The analytical solutions are also utilized to demonstrate reversals in the shear-sense patterns across the wedge. We expand this study by incorporating results from scaled laboratory experiments to evaluate applicability of the generalized theoretical model. It is shown from the theoretical model that the total pressure in the accretionary wedge dynamics becomes close to the lithostatic value when the rheological setting has low-viscosity (10¹⁹ Pa s) wedge materials.

Analysing the spatial arrangement, connectivity, and evolutionary history of complex fault networks is essential for quantifying strain distribution in active deformational zones, and evaluating associated geohazard and resource potentials. The structure and evolution of fault networks are commonly investigated using a range of methods, including the analysis of topographic data derived from satellite imagery, numerical modelling, as well as physical experiments. The high density and intrinsic complexity of fault systems in many study areas or models pose significant challenges for automated analysis, often necessitating time-intensive manual interpretation. Here, we present Fatbox, the Fault Analysis Toolbox, an open-source Python library that integrates semi-automated fault extraction with automated geometric and kinematic analysis of fault networks. The toolbox capabilities are demonstrated through three case studies on normal fault systems, each drawing on a different data type: (1) fault extraction and geometric characterization using GLO-30 topographic data in the Magadi-Natron basin in East Africa; (2) spatio-temporal tracking of fault development in vertical cross-sections of a forward numerical rift model; and (3) surface fault mapping and geometric evolution of a physical rifting experiment. Fatbox represents fault networks as topological graphs, comprising nodes (i.e., points) and edges (i.e., lines) connecting the nodes. In time-dependent models, the toolbox enables temporal tracking of faults, providing detailed insights into their geometric evolution and facilitating high-resolution measurements of fault kinematics. Fatbox offers a versatile and scalable framework that enhances the efficiency, reproducibility, and precision of fault system analysis – opening new avenues for tectonic research.

The volume increase that accompanies many hydration reactions can stress and fracture the surrounding rock, a process commonly called reaction-induced fracturing. Reaction-induced fracturing accelerates the rate of hydration by creating new pathways for fluids to migrate into reactive rock and by generating new reactive surface areas. The evolution of reaction-induced fractures also depends on the background stress state, which varies among different tectonic environments. We investigate the impact of tectonic stresses on reaction-induced fracturing using 2-D hydraulic-chemical-mechanical distinct element models. The results indicate that the general pattern of reaction-induced fractures depends on the orientation of background tectonic stresses relative to fluid-supplying channels. A spalling fracture pattern characterized by short cracks parallel to and along fluid-supplying channels occurs when the maximum principal tectonic stress is parallel to the channels whereas a branching fracture pattern characterized by long tensile cracks that propagate in a hierarchical manner into unreacted parts of the rock is expected when the tectonic stress is hydrostatic or when the maximum principal tectonic stress is normal to fluid-supplying channels. Spalling localizes hydration and fluid flow along the channels whereas branching promotes spatially extensive hydration and fluid flow away from the fluid supply. The results indicate tectonic stresses may guide the hydration distribution in the oceanic lithosphere at mid-ocean ridges and outer rises and in the cold mantle wedge corner in subduction zones.

We present TCSEIS-1D, a software to model the Earth's thermochemical and geophysical structure from the surface down to the core-mantle boundary (CMB). The code is designed to estimate geophysical parameters of the Earth's crust and mantle from petrological and thermal information within a thermodynamically consistent framework and to perform forward 1D coupled geophysical-petrological modelling of the structure of the Earth. Developed in Julia Language, the open-source code is intended to be an easy-to-use, flexible, and fast. TCSEIS-1D includes tools to exploit the large repertoire of 1D seismological data available, namely: surface wave dispersion curves (of fundamental and higher modes of Rayleigh and Love waves) and receiver functions (of P, S, and SKS waves). Surface heat flow and isostatic topography can also be modelled. Four simple examples that illustrate the capabilities of the code are presented to show the sensitivity of Rayleigh wave phase velocity curves and P-to-S receiver functions to compositional and temperature variations.

The search for a suitable host rock for the deep geological disposal of high-level radioactive waste is a major societal challenge of our time. In Germany, clay-bearing formations are under investigation to potentially host a repository for high-level radioactive waste (alongside rock salt and crystalline rock). Their intrinsic properties such as low permeability, self-sealing efficiency with respect to fractures, and sorption capacity provide promising conditions for long-term waste containment. However, these properties are dependent on numerous factors such as mineralogical composition, temperature and stress conditions, and water content. Among these factors, the burial history and thus compaction affect mineralogy, porosity, permeability, and mechanical properties. Within the framework of the MATURITY project, the impact of the burial history on these properties is investigated based on a combination of different laboratory and field methods. For this purpose, a Lower Jurassic claystone formation (the Amaltheenton-Formation, Fm) which was subjected to variable maximum depth and subsequent uplift during its burial history was chosen as target formation. At five locations, in the margin area of the Lower Saxony Basin (Germany) shallow boreholes were drilled through the formation where varying degrees of maturation indicate substantial differences in maximum burial depth.In this contribution, we present the first results of initial project steps that show (a) a similar clay-dominated mineralogical composition of the Amaltheenton-Fm across the borehole locations, (b) an increase of max. burial temperatures (83–169 °C) over a lateral distance of ∼ 50 km^{−5−7} m s^−1).

Long-period (LP) events and tremor are characteristic seismic signals of active volcanoes, offering insight into underlying fluid-driven processes. However, their emergent wavefield is complex and challenging to characterise. Here we decipher the LP event and tremor wavefield composition using a seismic array combined with a rotational sensor co-located with a seismometer (6C station). This study analyses and compares directional and phase velocity estimates by processing a 25 d long dataset from a rotational sensor and an array of seven broadband stations deployed at Mt. Etna, Italy, in August–September 2019. We derive the back azimuths (BAz) of LP events and tremor from both the seismometer array and the 6C station, and we compare these estimates with a reference BAz obtained from the network locations from the Istituto Nazionale di Geofisica e Vulcanologia-Osservatorio Etneo (INGV-OE) on Mt. Etna.Volcanic tremor occurs in distinct phases with varying seismic and surface activity. Depending on the phase, either the array or the 6C method provides reliable tremor BAz estimates, agreeing well with the INGV-OE reference. We find that BAz estimates of both methods are shifted southward relative to the reference location for the LP events. We attribute the larger southward deviation observed in the 6C results to local heterogeneities which exert a stronger influence on the 6C station than on the array.Based on the array derived slownesses we infer that the tremor and LP events mainly consist of surface waves. Further, the rotational sensor recordings suggest a wavefield dominated by SH-type waves. In combination with the observed temporal evolution of the 6C phase velocity in narrow frequency bands, we infer Love-wave dominance. This study highlights the value of a rotational sensor to constrain the wavefield in a deterministic way in a complex volcanic environment.

The North Sulawesi Subduction Zone is one of the youngest active subduction systems in the western Pacific. In western Sulawesi, the Palu–Koro strike–slip fault connects with the westward-extending North Sulawesi Trench, forming a distinctive subduction–transform fault system. Understanding the crustal structure beneath the Celebes Sea and the geometry of the Palu–Koro fault is crucial for assessing regional deformation, rupture dynamics, and seismic hazards. In this study, we analyse data from nine ocean bottom seismometers (OBSs) deployed across the Palu–Koro fault using the receiver function H–κ∼8 km depth) beneath the Celebes Sea, in contrast to significantly greater depths (∼25 km) beneath eastern Kalimantan and northern Sulawesi. Sharp variations in Moho depth near the Palu–Koro fault suggest the juxtaposition of two distinct crustal blocks. Combining S-wave velocity structures and local seismicity catalogue, we infer that the Palu–Koro fault is a left-lateral, through-going strike–slip fault extending into the Celebes Sea. These findings provide new geophysical constraints on the interplay between strike–slip faulting and subduction retreat, with implications for the generation of tsunamis by submarine earthquakes in this tectonically complex region.

Fatigue and damage accumulation in granitoids are classical, but poorly characterised, rock mechanics problems. We explore these phenomena by examining curling stone impacts. Curling stones are slid on ice and made to collide along a circumferential striking band. This well constrained scenario involves uniaxial compression of convex surfaces (i.e., Hertzian contacts). Conservatively, each stone experiences about 2900 impacts per season, over a lifespan of 10–15 years before refurbishment, providing a unique opportunity to study fatigue and damage accumulation under dynamic cyclic loading.Here, we first determine the stress magnitudes of head-on curling stone impacts using on-ice experiments involving a high-speed camera and pressure-sensitive films. We then characterise the damage observed in aged stones using photogrammetry, microtomography, and microscopy. For high-velocity impacts ($\mathrm{2.93}\&\#177;\mathrm{0.15}\mathrm{m}{\mathrm{s}}^{-\mathrm{1}}$), a curling stone is locally and momentarily stressed to 300–680 MPa, exceeding its quasi-static unconfined compressive strength and exceeding the threshold for fatigue damage for repeated dynamic loadings. Curling stone impacts are dynamic in nature, as evidenced by (1) high strain rates ($\mathrm{24}\&\#177;\mathrm{4}{\mathrm{s}}^{-\mathrm{1}}$) that lie below those of co-seismic rock pulverization; (2) ejection of rock powder during collisions and the presence of potential spalling microcracks; and (3) presence of striations on crescent-shaped fractures, which resemble mirror-mist-hackle patterns indicative of dynamic microcrack propagation. In the striking band, damage is confined to macroscopic Hertzian cone fractures and their immediate collet zones, and does not appear to extend beyond about 3–5 cm into the stones (radially). The circumferential density of cone fractures is limited to about 2–2.5 cm^−1.We propose that (1) early, high-velocity impacts initiate cone fractures up to a specific spatial density, and (2) with subsequent collisions in the same regions of the striking band, cone fractures progressively propagate and coarsen. This concentrates and channels the accumulated damage, shielding the rest of the stone from reaching critical stress levels for damage. Our findings are significant for applications where rocks are exposed to repetitive, high-stress impacts and suggest that narrow damage zones can dissipate high-impact stresses.

Understanding how the minerals in reservoir rocks respond to CO₂ injection is vital for the success and safety of Carbon Capture and Storage (CCS) projects. Feldspars are the most common mineral in the Earth's crust and act as primary framework grains in sandstones. Compared to quartz, feldspars are mechanically weak and chemically reactive. Dissolved feldspars can re-precipitate as clays, which in CCS reservoirs could impact fluid-flow. While caprock mineral stability is well studied, reservoir mineral reactivity, particularly of feldspars, remains understudied. To address this knowledge gap, we present microstructural and geochemical data from batch experiments that reacted CO₂-enriched fluids with feldspar-bearing sandstone sampled from the Captain Sandstone Member, the primary reservoir for the Acorn CCS Project (UK).Experiments were conducted in a hydrostatic pressure vessel at 70 MPaMPa°C, using CO₂-enriched water to simulate reservoir conditions. Pre- and post-reaction samples were analysed using XRD, SEM-EDS, and XCT to assess microstructural and mineralogical changes. Results show that CO₂:feldspar°C), incongruent dissolution of K-feldspar weakened grains which led to microfracturing. At 250 °C, CO₂Ca²⁺. Above 400 °C, coupled dissolution–precipitation processes were observed, including congruent K-feldspar dissolution, secondary porosity development, and localised precipitation of Ca-aluminosilicates and K-bearing phases around dissolving K-feldspars. These transformations could alter reservoir flow pathways and induce mechanical risks, i.e. destabilising nearby faults or initiating reservoir collapse. Given feldspars' prevalence in crustal rocks and CCS sandstone reservoirs, their reactive behaviour under in-situ conditions and in the presence of aggressive fluids demands greater attention.