Michelle Paulatto

We present 2D P‐wave velocity (Vp) models from the northern Ecuadorian subduction zone, north of the Carnegie Ridge. Data were collected during the HIPER2 3D wide‐angle seismic experiment, both onshore and offshore. Key seismic profiles were manually picked to determine P‐wave first‐arrival times, which were used for a traveltime tomographic inversion based on a Bayesian approach. Interpreting these 2D Vp models jointly with existing multi‐channel seismic (MCS) data reveals a high vertical Vp gradient (>0.85 km/s/km) consistent with the position of the forearc basement defined by MCS data, allowing us to map the basement along the margin. In addition, two notable low‐velocity zones are identified. The first zone observed across all profiles within the inner margin wedge, is interpreted as resulting from rock fracturation and/or alteration near the trench. The second one present in the subducting oceanic crust, is characterized by a Vp reduction of 0.5–1.0 km/s relative to the surrounding areas and marks the northern termination of a previously identified trench‐parallel velocities anomaly. As a possible origin of this distinctive anomaly, we propose the entry into subduction of an unmapped fracture zone (FZ), potentially reactivated by the increased plate bending due to the presence of the 2 km‐high Carnegie Ridge. Three FZ are proposed as possible sources of this anomaly that would southwards extend fossil transform faults for 100–150 km.

Porosity and permeability are crucial factors influencing hydrothermal flow in the oceanic crust. This paper provides a comprehensive overview of measurements and estimates of porosity and permeability. Although scientific drilling projects have yielded direct measurements of these properties, available data remain limited, particularly for very young oceanic crust (defined here as <1 Ma). Typically, porosity is estimated using indirect measurements of resistivity, seismic velocity, and gravity, while permeability can be directly assessed in boreholes, and inferred from heat flow, thermal structure or derived from porosity. Porosity decreases with depth and crustal age due to mechanical compression and infilling of void spaces. However, existing equations describing these trends are inadequate for modeling hydrothermal fluid flow. To address this, we compiled published petrophysical data on the spatial distribution of porosity in the oceanic crust and developed a new descriptive model of porosity variation with depth and crustal age, validated using seismic velocity data. From this porosity model, we estimated the permeability distribution using a refined empirical equation, with fitting parameters constrained by three‐dimensional numerical simulations of hydrothermal circulation near the ridge axis. Compared to previous studies, our porosity and permeability models more accurately represent observed spatio‐temporal variations and match outflow temperatures. Our improved models indicate that permeability in dikes beneath extrusive lavas near the ridge axis is higher than previously expected and is a critical condition for sustaining high‐temperature hydrothermal venting. This enhanced permeability may result from tectonic stress in the magmatic system, thermal cracking, or chemical dissolution driven by hydrothermal circulation.

Global copper demand is projected to increase from 22.8 Mt in 2024 to 35 Mt by 2040, driven largely by the transition to green energy technologies. Existing and announced Cu mining projects are forecast to meet only 70% of this demand by 2035, creating a significant supply deficit. Mining of subvolcanic magmatic brines - hypersaline and potentially supercritical fluids enriched in metals – has been proposed as an alternative source (Blundy et al., 2021). Here, we assess the potential mass of Copper Initially in Place (CIIP) in such reservoirs.Based on published resistivity models from 46 active magmatic-hydrothermal systems, we estimate the typical volume of brine reservoirs to range from 10 to 200 km3 and the average top reservoir depth to be 1.7 km, well within reach of modern drilling technology. Typical reservoir porosity in the shallow sub-critical zone is 8±6% and decreases to 3±3% in the deeper supercritical zone. Copper concentration in the brines is the most uncertain property. Data from fluid inclusions and Cu solubility modelling suggest that most brine reservoirs will host modest Cu concentration (ca. 10’s to 100’s ppm), but values could exceed 10,000 ppm in the most Cu enriched systems.We combine these estimates of reservoir volume, porosity and copper concentration using a probabilistic Monte Carlo framework to provide estimates of CIIP. Our analysis indicates a lognormal CIIP distribution with a median (P50) of 8.6 Mt and a P90 of 55 Mt, suggesting that individual magmatic brine resources may be comparable in size to conventional copper porphyry deposits. Moreover, a single high-flow-rate well tapping into a supercritical reservoir could produce approximately 2.4 kt of copper per year. A large-scale operation comprising multiple wells could yield 0.24 Mt/year, equivalent to roughly 1% of current global demand.A Cu brine mine could extract geothermal energy from the produced fluids. We envisage a self-powered Cu brine mine, with net positive energy per kg of Cu and a minimal environmental footprint. While significant challenges remain regarding exploration for copper-rich brine reservoirs and production of very hot and possibly supercritical brines, brine mining offers a potentially significant source of Cu that could be produced with much lower energy demand and negative environmental impact than conventional mining.Blundy, J., et al. "The economic potential of metalliferous sub-volcanic brines." Royal Society Open Science 8.6 (2021): 202192.

Serpentinization is a common geochemical process in ultramafic-hosted hydrothermal systems, where the hydration of mantle rocks releases heat and hydrogen that can support hydrothermal circulation and chemosynthetic ecosystems. Most current understanding of serpentinization kinetics and thermodynamic limits is primarily derived from closed-system laboratory experiments. Here, we investigate how this reaction operates within dynamically circulating fluid systems in nature. A simplified model for serpentinization as a function of temperature and fluid velocity was developed and implemented via three-dimensional numerical simulations using the IC-FERST flow simulator. Flow simulations explore how serpentinization interacts with fluid circulation and responds to variations in rock porosity and permeability. We apply this framework to a geologically realistic model of the Rainbow hydrothermal field (north Mid-Atlantic Ridge) to evaluate the combined effects of a deep magmatic heat source and reaction-driven heat generation. Results indicate that while the high vent temperatures and heat fluxes observed at Rainbow require a magmatic driver, serpentinization works synergistically with magmatic heat to temporarily elevate vent temperatures (by up to 50°C) and substantially increase seabed heat and fluid fluxes. Rather than being a uniformly progressing front, the serpentinization reaction is most effective in permeable regions surrounding the upwelling plume, where temperatures remain within an optimal thermodynamic window. Heat released by serpentinization has the unexpected effect of making upwelling plumes more stable in space and time, potentially contributing to sustaining black smoker vent fields over long periods of time (>10k years). By capturing key characteristics of the observed discharge at Rainbow, this study highlights how chemical reactions and fluid circulation jointly regulate hydrothermal activity and hydrogen production in ultramafic systems.

Porosity and permeability are crucial factors influencing hydrothermal flow in the oceanic crust. This paper provides a comprehensive overview of measurements and estimates of porosity and permeability. Although scientific drilling projects have yielded direct measurements of these petrophysical properties, available data remain limited, particularly for young oceanic crust. Typically, porosity is estimated using indirect measurements of resistivity, seismic velocity, and gravity, while permeability can be inferred from heat flow, thermal structure or derived from porosity. Porosity decreases with depth and crustal age due to mechanical compression and infilling of void spaces. However, existing equations describing these trends are inadequate for modeling hydrothermal fluid flow. To address this, we compiled published petrophysical data on the spatial distribution of porosity in the oceanic crust and developed a new descriptive model of porosity variation with depth and crustal age, validated using seismic velocity data. From this porosity model, we estimated the permeability distribution using a refined empirical equation, with fitting parameters constrained by three-dimensional (3D) numerical simulations of hydrothermal circulation near the ridge axis. Compared to previous studies, our porosity and permeability models more accurately represent observed spatio-temporal variations, reproduce expected patterns of vent distribution, and match outflow temperatures. Our improved models indicate that permeability in Layer 2B near the ridge axis is higher than previously expected and is a critical condition for sustaining high-temperature hydrothermal venting. This enhanced permeability may result from tectonic stress in the magmatic system, thermal cracking, or chemical dissolution driven by hydrothermal circulation.

The subduction margin in Ecuador is dominated by the subduction of the Carnegie Ridge and associated oceanic plate relief. This region is also affected by complex slip behaviour including aseismic deformation, slow slip, and large earthquakes. We present new seismic and gravity data collected as part of the HIPER campaign in 2020 and 2022, covering the subduction margin at the northern edge of the Carnegie Ridge. Traveltime tomography of dense active source wide-angle seismic data from a trench perpendicular profile reveals the structure of this part of the margin. The slab crust thickens from 7.5 km at the western end of the profile to 15 km at the eastern end. The profile crosses two seamounts (Atacames seamounts), one currently impinging onto the margin (AS2) and the other already buried beneath the accretionary prism (AS1). The seamounts have low P-wave velocity roots and are associated with gravity anomaly highs. The forearc is uplifted in front of the subducted seamount AS1 and is affected by gravitational collapse in its wake. In the area affected by the seamounts, the interseismic plate coupling is reduced to almost zero likely because of the fracturing and disruption of the forearc and lubrication induced by enhanced fluid input. Further downdip the profile extends into the rupture area of the 2016 M7.8 Pedernales earthquake. This part of the plate interface is more laterally homogeneous and characterised by higher Vp. Our results confirm that rugged plate relief is associated with reduced interseismic coupling and that megathrust earthquake rupture areas tend to have high Vp and laterally homogeneous properties.

Volcano deformation models contribute to hazard assessment by simulating magma system dynamics. Traditional magma reservoir pressure source shape assumptions often fail to replicate irregular, geophysically identified geometries. Uncertainties regarding the influence of reservoir geometry can limit the effectiveness of using deformation models to decipher unrest signals. Here, we aim to determine the feasibility of using a magma reservoir geometry directly derived from a seismic tomography survey in a volcano deformation model for Soufrière Hills Volcano, Montserrat. Three‐dimensional deformation models are created to simulate displacement using a pressure source geometry constrained from a low seismic velocity anomaly, inferred to be a region of partial melt, and contrasted against a traditional ellipsoid reservoir geometry. We also test a “hybrid” model combining a seismically inferred reservoir upper geometry and ellipsoidal base. Results of each model are evaluated against ground displacement observed on Montserrat from 2010 to 2022. Our results show that different reservoir geometries change the horizontal and vertical displacement fields across the island: the ellipsoid reservoir best reproduces vertical displacement magnitude, while the hybrid reservoirs best simulate horizontal displacement vectors and the region of maximum uplift. Overall, the ellipsoid‐shaped reservoir provides our best‐fit to the observed data, but we note this result could be biased due to prior years of optimization helping constrain the ellipsoid shape, size, and location. Our results show the potential for further use of geophysically constrained reservoir geometries in deformation modeling, and our methods could be applied to other deforming volcanoes worldwide.

The Kolumbo submarine volcano in the southern Aegean (Greece) is associated with repeated seismic unrest since at least two decades and the causes of this unrest are poorly understood. We present a ten-month long microseismicity data set for the period 2006–2007. The majority of earthquakes cluster in a cone-shaped portion of the crust below Kolumbo. The tip of this cone coincides with a low Vp-anomaly at 2–4 km depth, which is interpreted as a crustal melt reservoir. Our data set includes several earthquake swarms, of which we analyse the four with the highest events numbers in detail. Together the swarms form a zone of fracturing elongated in the SW-NE direction, parallel to major regional faults. All four swarms show a general upward migration of hypocentres and the cracking front propagates unusually fast, compared to swarms in other volcanic areas. We conclude that the swarm seismicity is most likely triggered by a combination of pore-pressure perturbations and the re-distribution of elastic stresses. Fluid pressure perturbations are induced likely by obstructions in the melt conduits in a rheologically strong layer between 6 and 9 km depth. We conclude that the zone of fractures below Kolumbo is exploited by melts ascending from the mantle and filling the crustal melt reservoir. Together with the recurring seismic unrest, our study suggests that a future eruption is probable and monitoring of the Kolumbo volcanic system is highly advisable.

Arc volcanoes are underlain by complex systems of molten‐rock reservoirs ranging from melt‐poor mush zones to melt‐rich magma chambers. Petrological and satellite data indicate that eruptible magma chambers form in the topmost few kilometres of the crust. However, very few chambers have ever been definitively located, suggesting that most are too short‐lived or too small to be imaged, which has direct implications for hazard assessment and modeling of magma differentiation. Here we use a high‐resolution technology based on inverting full seismic waveforms to image a small, high‐melt‐fraction magma chamber that was not detected with standard seismic tomography. The melt reservoir extends from ∼2 to at least 4 km below sea level (b.s.l.) at Kolumbo—a submarine volcano near Santorini, Greece. The chamber coincides with the termination point of the recent earthquake swarms and may be a missing link between a deeper melt reservoir and the high‐temperature hydrothermal system venting at the crater floor. The chamber poses a serious hazard as it could produce a highly explosive, tsunamigenic eruption in the near future. Our results suggest that similar reservoirs (relatively small but high‐melt‐fraction) may have gone undetected at other active volcanoes, challenging the existing eruption forecasts and reactive‐flow models of magma differentiation.

Seismic imaging methods have provided detailed three-dimensional constraints on the physical properties of magmatic systems leading to invaluable insight into the storage, differentiation and dynamics of magma. These constraints have been crucial to the development of our modern understanding of magmatic systems. However, there are still outstanding knowledge gaps resulting from the challenges inherent in seismic imaging of volcanoes. These challenges stem from the complex physics of wave propagation across highly heterogeneous low-velocity anomalies associated with magma reservoirs. Ray-based seismic imaging methods such as travel-time and surface-wave tomography lead to under-recovery of such velocity anomalies and to under-estimation of melt fractions. This review aims to help the volcanologist to fully utilize the insights gained from seismic imaging and account for the resolution limits. We summarize the advantages and limitations of the most common imaging methods and propose best practices for their implementation and the quantitative interpretation of low-velocity anomalies. We constructed and analysed a database of 277 seismic imaging studies at 78 arc, hotspot and continental rift volcanoes. Each study is accompanied by information about the seismic source, part of the wavefield used, imaging method, any detected low-velocity zones, and estimated melt fraction. Thirty nine studies attempted to estimate melt fractions at 22 different volcanoes. Only five studies have found evidence of melt storage at melt fractions above the critical porosity that separates crystal mush from mobile magma. The median reported melt fraction is 13% suggesting that magma storage is dominated by low-melt fraction crystal mush. However, due to the limits of seismic resolution, the seismological evidence does not rule out the presence of small (3) and medium-sized (3) high-melt fraction magma chambers at many of the studied volcanoes. The combination of multiple tomographic imaging methods and the wider adoption of methods that use more of the seismic wavefield than the first arriving travel-times, promise to overcome some of the limitations of seismic tomography and provide more reliable constraints on melt fractions. Wider adoption of these new methods and advances in data collection are needed to enable a revolution in imaging magma reservoirs.