Campi Flegrei last erupted in 1538 and periods of increased seismicity, gas emission and ground deformation occurred in the 50’s, 70’s 80’s and are ongoing since 2005. The eventual culmination of the unrest in an eruption, would directly impact on 2 million people living in the region, making it of critical concern for scientists, authorities and the public. Here, we use existing data, thermal modelling and calculations of the physical properties of magma, to provide plausible future scenarios, under the assumption that magma injection at 4-5 km depth is responsible for the unrest episodes recorded since 1950. Our calculations suggest that a critically pressurised reservoir containing potentially eruptible magma is present today at ~ 4 km depth. However, a major impediment to eruption is the reservoir volume, which would need 2-3 decades to grow to the size of the one that fed the last eruption of Campi Flegrei in 1538. Thermal modelling and numerical calculations suggest that potentially eruptible magma is present at a depth of around 4 km beneath Campi Flegrei, but that the magma reservoir volume is currently smaller in comparison to the last eruption in 1538.

I investigate earthquake-induced hydrological signals related to poroelastic deformation, thermal pressurization, fault-zone dilatancy and rupture of a pressurized reservoir at depth. This is performed using a two dimensional plane strain model that simulates ruptures on reverse and normal faults governed by rate-and-state friction coupled to elastic deformation and fluid flow along with spatio-temporal evolution of temperature and fault-zone permeability. The results show that whereas phenomena such as elastic deformation generate fluid pressure changes in the crust around faults, mechanisms such as shear heating and dilatancy drive localized fluid pressure perturbations on fault planes. The relaxation of fluid pressure anomalies is governed by the permeability, which varies with depth and on faults due to transient fracturing and healing. Strong increases in permeability on fault planes during rupture favor rapid fault-parallel fluid flow during and immediately following earthquakes. In addition, fluid pressure perturbations disperse laterally and decay rapidly close to the surface whereas they remain localized and persist for far longer due to low permeabilities at depth. I conclude that fluid pressure perturbations and fluid flow in and around ruptured faults may result from a range of interacting processes that may operate to varying degrees at different depths, positions relative to a fault and tectonic regimes.

Understanding the conditions and mechanisms that produce earthquakes is of high scientific relevance. The central Southern Alps/Kā Tiritiri o te Moana of New Zealand is an active orogen that offers a unique opportunity to study the processes that drive seismogenesis. A new high‐quality, matched‐filter‐based microseismicity catalog has been constructed by following a fully automated detection and location process. The catalog spans from 2009 to 2020 with local magnitudes between −1.81 and 3.42. Our results indicate a seasonal pattern in earthquake occurrence, with a notable correlation between shallow‐depth earthquakes (6 km hypocentral depths) and large, mostly summer, rainfall events beneath three separate glaciers. We hypothesize that a combination of seasonal snowmelt and heavy rainfall events raises the water table during spring and summer, changing pore‐fluid pressure in the upper crust and triggering earthquakes. Our findings highlight the role of extreme rainfall and glacier dynamics in triggering shallow earthquakes, which can improve hazard assessment in the central Southern Alps/Kā Tiritiri o te Moana and similar alpine regions worldwide.

Earthquakes in fluid-saturated rocks induce sudden changes in pore-pressures that can lead to appreciable postseismic deformation. However, earthquakes can also release fluids from overpressured parts of the crust, which can also contribute to additional postseismic effects. In this study, we use two-dimensional poroelastic models to investigate postseismic deformation and fluid pressures following ruptures on overpressured dip-slip faults that slide according to rate- and state-dependent friction. We show that when the crust prior to rupture has pore pressures in hydrostatic equilibrium, then ruptures induce fluid pressure anomalies according to the field of coseismic elastic volumetric strain. These pore pressure anomalies relax with time to produce characteristic postseismic deformation that depends on the slip magnitude and fault style, as typically observed. However, very different results are obtained if the crust is appreciably overpressured at the time an earthquake is nucleated. In this case, the poroelastic response is overwhelmingly dominated by drainage and fluid pressure drop within the overpressured crust, which is facilitated by an increase in permeability on the fault during rupture. This results in transient postseismic subsidence that occurs irrespective of the faulting style, fault geometry, slip magnitude or details of the coseismic strain field. The time scale and magnitude of this postseismic subsidence are controlled by the magnitude of the fluid overpressure prior to rupture, the maximum coseismic permeability and how rapidly the fault permeability recovers following an earthquake. The poroelastic effects associated with rupturing of overpressured faults may be at least an order of magnitude greater that the classic poroelastic response (i.e., relaxation of pore pressures generated by coseismic elastic volumetric strain). Overall, our results highlight the potentially dramatic effect that the breaching of deep overpressured fluid reservoirs can have on fluid pressures and surface displacements following earthquakes.

Shear stress levels on reverse faults are anticipated to be several times higher than on normal faults with the same pore pressure ratio. In addition, ruptures on normal faults release gravitational potential energy, whereas earthquakes on reverse faults expend work in uplifting rocks. In this study, I investigate the significance of these differences for earthquake cycles and I question whether the source of energy driving earthquakes is the same on reverse and normal faults. Based on the assumption that normal and reverse faults have the same background frictional properties and pore pressure states, I use numerical simulations with a two-dimensional dynamic elastic-plastic model to show that due to stress differences, earthquakes on reverse faults tend to occur less frequently, produce more coseismic slip and stress drop and involve higher slip rates than ruptures on normal faults with equivalent dimensions. The analysis also shows differences in the energy changes associated with earthquake cycles on reverse and normal faults. However, the earthquakes on both fault types result from abrupt release of elastic strain energy, which proceed and essentially drive variations in gravitational potential energy. Thus, ruptures on both normal and reverse faults are consistent with elastic rebound theory.

Summary Faults in the upper crust are sometimes thought to act as self-sealing valves, episodically releasing highly overpressured fluids trapped at greater depth during earthquakes. They are also often considered to be capable of actively pumping fluids into or out of faults in response to coseismic volumetric strain, thermal pressurisation or other mechanisms. In this study we investigate how these different types of behaviour (i.e., valve versus pump) are manifested in earthquakes. We do this using a two dimensional plane strain model where frictional sliding on a thrust fault that is fed by a fluid source at its base is coupled to porous flow, thermal pressurisation and strong variations in permeability. Our results show that thermal pressurisation leads to dramatic dynamic weakening that produces earthquakes that propagate as slip pulses producing large stress drop, large slip and high slip velocities. On the other hand, valve-type behaviour typically produces smaller, less energetic earthquakes that commonly arrest before rupturing the entire fault. In some valve-models, we observe complex compound ruptures and swarm activity, which is linked to the ascent of a propagating fluid pressure pulse driven by a large increase in permeability during sliding. Both pump and valve mechanisms can produce anomalously weak faults, though they are each associated with distinctly different fluid pressure and strength evolution over the seismic cycle and during rupture. Our models highlight the complex way in which fluids may interact with earthquakes, especially if valve and pump models coexist.

Downward flow of surface-derived water deep into the upper crust is investigated using 2-D coupled hydrothermal numerical models. In the models, downward flow is driven by either topographic gradients or seismic pumping, while it is facilitated by large episodic variations in fault permeability, intended to mimic fracturing and healing on a fault over repeated seismic cycles. The models show that both forcing scenarios are equally capable of driving surface-derived fluid to the base of faults at 10 km depth in several tens of thousands of years under certain conditions. Downward flow of cold fluid occurs almost exclusively during and shortly after earthquakes, while during the remaining portion of the seismic cycle fluids remain relatively stationary while they undergo thermal relaxation (i.e. heating). Rapid downward flow is favoured by a large coseismic permeability, long permeability healing timescale and large coseismic dilatancy or high topographic relief above the fault at the surface. However, downward fluid flow is completely inhibited if fluid pressures exceeds the hydrostatic gradient, even by modest amounts, which suggests that deep fluid infiltration is unlikely to occur in every region.

The strength and sliding behavior of faults in the crust is largely controlled by friction and effective stress, which is itself modulated by fluid pressure. Most earthquake models assume a fixed pore fluid pressure despite widespread evidence that is varies strongly in time due to changes in permeability. Here we explore how dynamic changes in pore pressure influence the properties of earthquakes in the upper crust. To study this problem we develop a two dimensional model that incorporates slow tectonic loading and fluid pressure generation during the interseismic period with frictional sliding on a thrust fault whose permeability evolves with slip. We find that the presence of relatively modest fluid overpressures tends to reduce coseismic slip, stress drop, maximum sliding velocity, rupture velocity and the earthquake recurrence time compared to models without fluids. Our model produces a wide range of sliding velocities from rapid to slow earthquakes, which occur due to the presence of high pore pressures prior to rupture. The models also show evidence for aftershocks that are driven by fluid transfer along the fault plane after the mainshock. Overall, this study shows that fluids can exert an important influence on earthquakes in the crust, which is mostly due to modulation of the effective stress and variations in permeability, and to a lesser extent to poro‐elastic coupling.

<p class="paragraph"><span class="normaltextrun"><span lang="EN-US">The strength and sliding behavior of faults in the upper crust are largely controlled by friction and effective stress, which is itself modulated by the fluid pressure. However, while many studies have investigated the role of friction on the earthquake cycle, relatively little effort has gone into understanding the effects linked to dynamic changes in fluid pressure. Here, we explore coupled interactions between slow tectonic loading and fluid pressure generation during the interseismic period with rapid sliding and elastic stress transfer during earthquakes on a plane strain thrust fault in two dimensions. Our models incorporate rate- and state-dependent friction along with dramatic changes in the fault permeability during sliding. In these modes, earthquakes are nucleated where fluid pressures are locally high and then propagated as slip pulses onto stronger parts of the fault. For the model without overpressure, the ruptures are more crack-like. Our model produces a wide range of sliding velocities from rapid to slow earthquakes, which occur due to the presence of high pore pressures prior to rupture. The models also show evidence for aftershocks that are driven by fluid transfer along the fault plane after the mainshock. Overall, we find that the presence of relatively modest fluid overpressures tends to reduce coseismic slip, stress drop, maximum sliding velocity, rupture velocity, and the earthquake recurrence time relative to ruptures in a dry crust. This study shows that fluids can exert an important influence on earthquakes in the crust, which is mostly due to modulation of the effective stress and variations in permeability, and to a lesser extent to poroelastic coupling. </span></span></p>

I use a dynamic two-dimensional plane strain model of an elasto-plastic (Mohr-Coulomb) material with velocityweakening friction to numerically simulate the emergence and propagation of shear fractures that accumulate slip intermittently during earthquakes. The model considers a 10 x 10 km block of homogeneous crust with a small weak inclusion, subjected to slow simple shear. Results show that deformation is distinctly bimodal, consisting of long periods (lasting ca. 50-200 years) where deformation is dominantly elastic separated by rapid sliding events lasting a few seconds during which time deformation is strongly localised on narrow plastic shear bands (faults). In terms of energy expenditure, the interseismic period is overwhelming dominated by accumulation of elastic strain energy whereas during earthquakes, most of the drop in elastic strain energy is consumed (dissipated) by plastic work. Model earthquakes have maximum slip rates of a few meters per second, involve a few meters of slip and result in drop of mean differential stress of several megapascals. Most earthquakes are complex events involving near-simultaneous rupture of multiple fault segments that propagate at supershear velocities (close to the P-wave speed) while they also induce a significant amount of more diffuse offfault inelastic deformation. Earthquakes may involve formation of new faults and/or reshear on previously formed faults, which are favourably reactivated owing to their low pressure. Most individual faults establish much of their length early, whereas during subsequent events they continue to accumulate displacement at virtually constant length. As the confining pressure is increased, ruptures are more dynamic, which leads to increasingly widespread inelastic deformation. Overall, the models highlight the complex temporal and spatial interactions that exist between different faults within an array that communicate especially during earthquakes through static and dynamic changes in the stress field.

Understanding how folds and faults nucleate and grow is key to unravelling the tectonic and seismic evolution of both active and fossil fold-and-thrust belts (FATB). The progressive growth of folds and the transition from folding to faulting in FATBs are complex phenomena that reflect the combined effects of numerous deformation processes and boundary conditions. To better understand these complexities, we studied a folded sequence within the shortened Mesozoic carbonate multilayer succession of the seismically active Italian Eastern Southern Alps (ESA). The studied mesoscopic folds are parasitic to hanging- and footwall hectometric folds associated with regional-scale S-verging thrusts. We aimed to constrain (1) the folding style of the area, (2) the parameters governing the transition from folding to faulting through time, (3) the seismic vs. aseismic behaviour during the folding-faulting transition in carbonate-dominated fold-and-thrust belts, and (4) the overall tectonic framework of the ESA. Our approach relied on i) the structural analysis of symmetric and asymmetric folds and of the locally associated thrusts to assess the overall structural style and derive geometrical constraints upon the documented deformation features, ii) XRD analysis of the deformed carbonate multilayer to define its mineralogical composition and to establish the influence thereof upon deformation, and iii) mechanical modelling based on the Finite Element Method (FEM) to study the factors governing fold symmetry versus asymmetry. Our field analysis shows that folds evolve from symmetric and open to south-verging asymmetric and close to tight before eventually being decapitated by discrete faults. This occurs once fold forelimbs exceed ~80°, which corresponds roughly with when the ratio between fore- and backlimbs dip angle exceeds ~3.3. The mesoscopic thrusts that dissect asymmetric folds firstly localise along the gently dipping backlimbs, exploiting clay-rich beds therein, and then propagate toward the foreland by cutting across the steep forelimbs, producing cataclastic domains. Layer-parallel shearing and cataclasis are the dominant deformation modes during thrusting along the backlimb and forelimb, respectively. FEM modelling, used to constrain the transition from symmetric to asymmetric folding, shows that it is mainly controlled by (i) the thickness and vertical distribution of different rock types and (ii) the growth of first order folds at larger scales. In multilayer sequences we observe that small scale folds are initially symmetrical, forming under pure shear conditions. However, these structures may later become passively rotated in simple shear as they become parasitic to the growth of larger scale folds. Finally, we propose a scenario of fold growth and transition from folding to faulting that has implications on the tectonic evolution of fold-and-thrust belts, including the coexistence of seismic and aseismic deformation during progressive shortening.

The Toba volcanic system in Indonesia has produced two of the largest eruptions (>2,000 km3 dense-rock equivalent [DRE] each) on Earth since the Quaternary. U-Pb crystallization ages of zircon span a period of ∼600 ky before each eruptive event, and in the run-up to each eruption, the mean and variance of the zircons' U content decrease. To quantify the process of accumulation of eruptible magma underneath the Toba caldera, we integrated these observations with thermal and geochemical modeling. We show that caldera-forming eruptions at Toba are the result of progressive thermal maturation of the upper crustal magma reservoir, which grows and chemically homogenizes, by sustained magma influx at average volumetric rates between 0.008 and 0.01 km3/y over the past 2.2 My. Protracted thermal pulses related to magma-recharge events prime the system for eruption without necessarily requiring an increased magma-recharge rate before the two supereruptions. If the rate of magma input was maintained since the last supereruption of Toba at 75 ka, eruptible magma is currently accumulating at a minimum rate of ∼4.2 km3 per millennium, and the current estimate of the total volume of potentially eruptible magma available today is a minimum of ∼315 km3 Our approach to evaluate magma flux and the rate of eruptible magma accumulation is applicable to other volcanic systems capable of producing supereruptions and thereby could help in assessing the potential of active volcanic systems to feed supereruptions.

Zircon occasionally crystallizes in evolved melt pockets in mafic large igneous province (LIP) magmas, and in these cases, it is used to provide high-precision age constraints on LIP events. The precision and accuracy of high-precision ages from LIPs are crucially important, because they may be implicated in mass extinctions. However, why zircon crystallizes in these magmas is not clearly understood, since their mafic compositions should limit zircon saturation. Here, we investigate the occurrence of zircon (and baddeleyite) in intrusive and extrusive mafic rocks from Central Atlantic Magmatic Province (CAMP) using petrography, trace-element analysis, Ti temperatures, Hf and oxygen isotopes, and high-precision U–Pb geochronology, along with petrological and thermal modeling. We provide new ages for CAMP sills that intruded into Paleozoic sediments in Brazil, indicating that the high and low Ti magmatism in this area occurred synchronously over 264 ± 57 ka. We show that upper crustal assimilation, especially of shales, during the emplacement of the CAMP likely led to zircon saturation. Assimilation of upper crustal sediments is also supported by high δ 18 O values and some rare negative εHf values in the zircon crystals. The only extrusive sample analyzed was the North Mountain basalt in Nova Scotia, Canada. This sample contains a large age variation in its zircon crystals (up to 4 Ma), and the older crystals have slightly more negative εHf values suggesting the presence of small (micron scale) xenocrystic cores associated with very late-stage sediment assimilation. However, the CAMP dataset as a whole suggests that the presence of xenocrystic cores is rare. Assuming no xenocrystic cores, and considering the zircon undersaturated nature of LIP mafic melts, the oldest zircon age clusters in a population should record the magma emplacement (or time when assimilation occurred), and the younger ages in a population are more likely to reflect Pb loss, especially given the high U concentrations of LIP zircon. Our identification of heterogeneous isotopic and elemental compositions in LIP zircon indicates that zircon in these magmas saturate in isolated minute melt pockets just before the system cools below its solidus.

Fluvial stratigraphy is the product of changes in Earth’s history and inverting this record has often resulted in interpretations associated with changes in base-level caused by sea-level and/or basement subsidence (downstream drivers). Similarly, environmental perturbations occurring in the upstream reaches of a fluvial system (i.e., the source region), such as climate driven changes of water discharge and/or perturbations of sediment supplied to rivers (upstream drivers), can also drive river bed evolution. Therefore, both changes in upstream and downstream drivers can cause a river’s equilibrium profile to respond and adjust through aggradation or degradation and hence generate stratigraphy. Furthermore, it is likely to have changes in both upstream and downstream drivers simultaneously because both drivers may be themselves driven by the same factors e.g., astronomical cycles can drive both sea-level variation at the downstream end of fluvial systems and water discharge variations in the upstream end. Deciphering the effects of the two drivers is vital to be able to comprehensively interpret the narrative of Earth’s history preserved in fluvial successions. We explore this issue with river flume experiments, where we are able to test the influence of both upstream and downstream drivers in isolation. Furthermore, the small scale of physical modelling reduces the spatial and temporal timescales compared to natural systems and allows us to investigate how quickly the system responds. We use a narrow (0.05 m), long (2.25 m) flume with an initial gradient of zero. Side-profile photos are taken throughout the experiment run, which are then analysed and fitted to monitor river bed evolution. Top view photos record channel dimensions. We use low flow rates (~<600 ml/min) delivered by a peristaltic pump, to avoid turbulence and ensure bedload transport. We have three aims with our experiments. Firstly, to investigate the role of changes in water discharge and sediment supply on equilibrium river profiles and the timescales associated. Secondly, to carry out a series of perturbation experiments varying downstream drivers (i.e., sea-level), which theoretically produce the same amount of aggradation as the upstream parameters we have used in order to compare. Thirdly to vary both upstream and downstream parameters simultaneously to investigate the effects. Results to date suggest that the growing wedge maintains a relatively constant slope and that the slope of the wedge is dependent on sediment concentration (sediment discharge/water discharge), when using the same grain-size distribution for each experiment. Furthermore, results imply that the system is highly sensitive to perturbations when the setup of the system is with relatively low sediment concentrations. Therefore, a greater magnitude of response is seen than with setups of higher sediment concentrations. Currently we are undergoing perturbation experiments and downstream perturbations, the results of which will also be presented here. Ultimately we will use our findings to upscale our experiments into a fully 3-D flume tank that will grow as an unconfined fan in order to observe any similarities and differences.

Rock falls and landslides plunging into lakes or small reservoirs can result in tsunamis with extreme wave run-ups. The occurrence of these natural hazards in populated areas have encouraged a recent sharp increase of studies that aim to mitigate their impact on human lives and assess infrastructure lost. This paper amalgamates in a novel fashion and at an unprecedented detail in situ historic measurements, geological data and numerical modeling of a rock fall event and associated tsunami wave that occurred in Lake Lovatnet (western Norway) in September 1936. Historical records report an event that released ca. 1 million m 3 of rocks and debris from Ramnefjellet Mountain at an altitude of 800 m above Lake Lovatnet. The fragmented material plunged into the lake, causing a tsunami that reached a maximum run-up of 74 m and killed 74 people. In fact, the settlements of Bødal and Nesdal were wiped out as a result of the catastrophic wave. Sediments resulting from the 1936 rock fall and associated tsunami were identified in the subsurface of Lake Lovatnet by shallow geophysical investigations and were retrieved using gravity coring equipment. A set of high resolution physical and geochemical measurements were carried out on the cores with the aim of reproducing a highly detailed reconstruction of this catastrophic event in order to better understand and learn about the processes involved. The cores were retrieved in the northwestern sub-basin of the lake and its chronology was constrained by 210 Pb and radiocarbon dating. A specially tailored physically based mathematical model was applied to better understand the tsunami event. Integration of the geophysical record, the sedimentological data and numerical modeling provide a comprehensive background to better understand the effects of such event in a deep fjord-like lacustrine basin and to generate information for better mitigation of similar events elsewhere.

Four voluminous ignimbrites (150–500 km 3 ) erupted in rapid succession at 27 Ma in the central San Juan caldera cluster, Colorado. To reconstruct the timescales and thermal evolution of these magma reservoirs, we used zircon ID-TIMS U–Pb geochronology, zircon LA-ICP-MS geochemistry, thermal modeling, and zircon age and crystallization modeling. Zircon geochronology reveals dispersed zircon age spectra in all ignimbrites, with decreasing age dispersion through time that we term a ‘chimney sweeping’ event. Zircon whole-grain age modeling suggests that 2σ zircon age spans represent approximately one-quarter of total zircon crystallization timescales due to the averaging effect of whole-grain, individual zircon ages, resulting in zircon crystallization timescales of 0.8–2.7 m.y. Thermal and zircon crystallization modeling combined with Ti-in-zircon temperatures indicates that magma reservoirs were built over millions of years at relatively low magmatic vertical accretion rates (VARs) of 2–5 × 10 –3 m y −1 (2–5 × 10 –6 km 3 y −1 km −2 ), and we suggest that such low VARs were characteristic of the assembly of the greater San Juan magmatic body. Though we cannot unequivocally discern between dispersed zircon age spectra caused by inheritance (xenocrystic or antecrystic) versus prolonged crystallization from the same magma reservoir (autocrystic), our findings suggest that long-term magma input at relatively low VARs produced thermally mature upper crustal magma reservoirs resulting in protracted zircon crystallization timescales. Compiling all U–Pb ID-TIMS zircon ages of large ignimbrites, we interpret the longer timescales of subduction-related ignimbrites as a result of longer term, lower flux magmatism, and the shorter timescales of Snake River Plain ignimbrites as a result of shorter term, higher flux magmatism.

The Holuhraun-Bardarbunga (Iceland) eruption lasted approximately 6 months. Magma propagated laterally through a 40 km long dyke, while Bardarbunga caldera was collapsing. This event was intensely monitored, providing an opportunity to investigate the relationships between eruption dynamics and erupted products. Whole rock and melt inclusion data do not show chemical variations of magma during the eruption. Nevertheless, zoning patterns in clinopyroxene suggest temporal variations of intensive parameters during crystallization. We investigated the chemical zoning of clinopyroxene using a data driven approach, on major and trace elements analyses from lava flow lobes emplaced during the eruption. We applied hierarchical clustering (HC) to identify compositional groups based on major and trace element chemistry. This analysis identifies five compositional groups, which can be associated with specific petrographic features. One cluster represents the chemistry of hourglass sectors, two constitute the oscillatory zoned mantle of the crystals, one cluster corresponds to a seldom present bright rim (in back scattered electron images) in the outer portions of the crystals, and a last one represents most of the outer rims. HC applied to trace elements also identifies five compositional clusters, which highlight progressively more evolved clinopyroxene compositions from the core to the rim of the crystals. Two of the clusters identified with trace elements corresponds to major element clusters. All together the data suggest that the chemical zoning in the inner portions of the clinopyroxene crystals was generated by crystallization in the magma reservoir and interaction between hot magma propagating through the dyke and unerupted magma cooling within the dyke. The fraction of zones produced by interaction with colder portion of the magma residing within the dyke dropped during the eruption, potentially signaling the thermal maturation of the dyke. Some of the analyses reveal that relatively close to the eruption time (i.e., the outer portions of the crystals) the dyke intercepted a lens of low temperature magma with a chemical composition that is distinguishable from the 2014 to 2015 Bardarbunga eruption. Our approach can provide insights on the evolution of deep processes occurring during long-lasting eruptions by combining the analysis mineral chemistry of erupted products with multiparametric monitoring signals.