Discrete Fault Research Articles

Benchmarking numerical simulation of induced fault slip with semi-analytical solutions

AbstractPore pressure fluctuation in subsurface reservoirs and its resulting mechanical response can cause fault reactivation. Numerical simulation of such induced seismicity is important to develop reliable seismic hazard and risk assessments. However, modeling of fault reactivation is quite challenging, especially in the case of displaced faults, i.e., faults with non-zero offset. In this paper, we perform a systematic benchmarking study to validate two recently developed numerical methods for fault slip simulation. Reference solutions are based on a semi-analytical approach that makes use of inclusion theory and Cauchy-type singular integral equations. The two numerical methods both use finite volume discretizations, but they employ different approaches to represent faults. One of them uses a conformal discrete fault model (DFM) while the other employs an embedded (non-conformal) fault model. The semi-analytical test cases cover a vertical frictionless fault, and inclined displaced faults with constant friction and slip-weakening friction. It was found that both numerical methods accurately represent pre-slip stress fields caused by pore pressure changes. Moreover, they also successfully cope with a vertical frictionless fault. However, for the case with an inclined displaced fault with a constant friction coefficient, the embedded method can not converge for the post-slip phase, whereas the DFM successfully coped with both constant and slip-weakening friction coefficients. In its current implementation, the DFM is therefore the model of choice when accurate simulation of local faulted systems is required.

Fault structure and earthquake clustering in Aswan region (Egypt) revealed by high-precision earthquake location from 35 years of recorded natural and induced seismicity

Starting from an initial catalogue of 7833 natural and reservoir-induced seismic events collected in Aswan region (south Egypt) from 1982 to 2016, we investigate the fault structure and triggering mechanisms by determining high-resolution hypocenters for 2562 earthquakes. Despite the complex network of intersecting fractures, high-precision earthquake locations reveal numerous discrete fault strands (some not mapped yet), whose kinematics have been determined from the focal mechanisms of Ml ≥ 2.5 earthquakes. Furthermore, the analysis of the space-time evolution of seismicity indicates an eastward migration of earthquakes and a progressive activation of different faults. This process could reflect fluid migration in the Wadi Kalabsha embayment likely controlled by permeability barriers at depth acting as seals, and the subsequent build-up of the pore pressure as the dominant driving mechanism of the observed seismicity in the region. A strong spatio-temporal earthquake clustering is observed in the region characterized by seismic sequences, repeated earthquakes, and long-lasting swarms. High variability of b-value in correspondence of the occurrence of mainshock-aftershock sequences also suggests the activation of faults and fractures within their respective fault zones under lower differential stress conditions due to fluids. The projection of earthquake hypocenters on an E-W vertical depth section of the study area shows a seismic gap with an approximate length of about 11 km along the Kalabsha fault, which suggests the presence of a locked fault patch that may generate a Mw 5.9 earthquake if this segment were to break in a single rupture episode.

Revised geologic map and structural interpretation of the Mineral King pendant, southern Sierra Nevada, California (USA): Evidence for kilometer-scale folding and structural imbrication of a Permian to mid-Cretaceous volcanosedimentary assemblage

Abstract The Mineral King pendant is an ~15-km-long, northwest-striking assemblage of Permian to mid-Cretaceous metavolcanic and metasedimentary rocks that form a steeply dipping wall-rock screen between large mid-Cretaceous plutons of the Sierra Nevada batholith (California, USA). Pendant rocks are generally well layered and characterized by northwest-striking, steeply dipping, layer-parallel cleavage and flattening foliation and steeply northwest-plunging stretching lineation. Northwest-elongate lithologic units with well-developed parallel layering and an absence of prominent faults or shear zones suggests a degree of stratigraphic continuity. However, U-Pb zircon dating of felsic metavolcanic and volcanosedimentary rocks across the pendant indicates a complex pattern of structurally interleaved units with ages ranging from 277 Ma to 101 Ma. We utilize a compilation of 39 existing and new U-Pb zircon ages and four reported fossil localities to construct a revised geologic map of the Mineral King pendant that emphasizes age relationships rather than lithologic or stratigraphic correlations as in previous studies. We find that apparently coherent lithologic units are lensoidal and discontinuous and are cryptically interleaved at meter to kilometer scales. Along-strike facies changes and depositional unconformities combine with kilometer-scale tight folding and structural imbrication to create a complex map pattern with numerous discordant units. Discrete faults or major shear zones are not readily apparent in the pendant, although such structures are necessary to produce the structural complications revealed by our new mapping and U-Pb dating. We interpret the Mineral King pendant to be structurally imbricated by a combination of kilometer-scale tight to isoclinal folding and cryptic faulting, accentuated by, and eventually obscured by, pervasive flattening and vertical stretching that preceded and accompanied emplacement of the bounding mid-Cretaceous plutons. Deformation in the Mineral King pendant represents a significant episode of pure-shear-dominated transpression between ca. 115 Ma and 98 Ma that adds to growing evidence for a major mid-Cretaceous transpressional orogenic event affecting the western U.S. Cordillera.

Forecasting fluid-injection induced seismicity to choose the best injection strategy for safety and efficiency.

Induced seismicity poses a challenge to the development of Enhanced Geothermal Systems (EGS). Improving monitoring and forecasting techniques is essential to mitigate induced seismicity and thereby fostering a positive perception of EGS projects among local authorities and population. Induced seismicity is the result of complex and coupled thermo-hydro-mechanical-chemical mechanisms. Injection flux and pressure are crucial controlling parameters for both hydraulic stimulation and circulation protocols. We develop a methodology combining a hydro-mechanical model with a seismicity rate model to estimate the magnitude and frequency of mainshocks and aftershocks induced by fluid injection. We apply the methodology to the case of the Basel EGS (2006, Switzerland) to compare the effects of progressive, cyclic and constant injections on the mechanical response of discrete faults. Results from the coupled hydro-mechanical models show that the pore pressure diffusion and consequent enhancement of fault permeability are limited to the vicinity of the injection well during cyclic injection. Additionally, constant injection induces seismicity from the start of the injection but enhances the permeability of most of the faults within a shorter duration, inducing less post-injection seismicity. The methodology can be adapted to any numerical model and allows new projects to be developed by anticipating the safest injection protocol.This article is part of the theme issue 'Induced seismicity in coupled subsurface systems'.

Quake-DFN: A Software for Simulating Sequences of Induced Earthquakes in a Discrete Fault Network

ABSTRACT We present an earthquake simulator, Quake-DFN, which allows simulating sequences of earthquakes in a 3D discrete fault network governed by rate and state friction. The simulator is quasi-dynamic, with inertial effects being approximated by radiation damping and a lumped mass. The lumped mass term allows for accounting for inertial overshoot and, in addition, makes the computation more effective. Quake-DFN is compared against three publicly available simulation results: (1) the rupture of a planar fault with uniform prestress (SEAS BP5-QD), (2) the propagation of a rupture across a stepover separating two parallel planar faults (RSQSim and FaultMod), and (3) a branch fault system with a secondary fault splaying from a main fault (FaultMod). Examples of injection-induced earthquake simulations are shown for three different fault geometries: (1) a planar fault with a wide range of initial stresses, (2) a branching fault system with varying fault angles and principal stress orientations, and (3) a fault network similar to the one that was activated during the 2011 Prague, Oklahoma, earthquake sequence. The simulations produce realistic earthquake sequences. The time and magnitude of the induced earthquakes observed in these simulations depend on the difference between the initial friction and the residual friction μi−μf, the value of which quantifies the potential for runaway ruptures (ruptures that can extend beyond the zone of stress perturbation due to the injection). The discrete fault simulations show that our simulator correctly accounts for the effect of fault geometry and regional stress tensor orientation and shape. These examples show that Quake-DFN can be used to simulate earthquake sequences and, most importantly, magnitudes, possibly induced or triggered by a fluid injection near a known fault system.

Earthquake Relocations Delineate a Discrete Fault Network and Deformation Corridor Throughout Southeast Alaska and Southwest Yukon

AbstractDeformation in southeastern Alaska and southwest Yukon is governed by the subduction and translation of the Pacific‐Yakutat plates relative to the North American plate in the St. Elias region. Despite notable historical seismicity and major regional faults, studies of the region between the Fairweather and Denali faults are complicated by glacial coverage and the remote setting. In the last decade, significant improvements have been made to the density of regional broadband seismometer networks. We relocate more than 5,000 earthquakes between 2010 and 2021 in the region of southeastern Alaska and southwestern Yukon utilizing these improved seismic networks. With reductions in catalog uncertainty, particularly in depth, we quantify the thickness of the seismogenic layer in the crust throughout the region and locate seismicity on a shallow network of upper‐crustal faults. Relocated earthquakes, combined with an updated focal‐mechanism catalog, permit estimating and classifying motion of active faults. This includes mapping the Totschunda‐Fairweather “Connector” fault, which plays an important role in explaining regional deformation, and identifying new faults like the Kathleen Lake fault. We draw similarities between our seismic observations and simplified conceptual models of regional tectonics, which describe a dominant transpressional regime and localized slip partitioning. Our results support a hypothesis where current deformation is taking place on a well‐defined and evolved network of shallow faults in the corridor between the Totschunda‐Fairweather “Connector” and Denali faults.

Purification and production of bio-ethanol through the control of a pressure swing adsorption plant

Bioethanol can be used as fuel obtained from second-generation raw material (cane bagasse) in order not to affect food sovereignty. One of the processes that have achieved a greater production and recovery of bioethanol is pressure swing adsorption (PSA), which uses zeolites to separate and purify the ethanol-water mixture. The aim of this work focuses on implementing a discrete Fault Tolerant Control and discrete PID on a virtual PSA plant for ethanol production maintaining the purity stable under the effects of combined faults in the actuator (flow valve) that can affect the PSA plant. It was observed that both controllers have great performance implementing it in the Hammerstein–Wiener model, but when performing the tests with the PSA plant, the FTC presented greater robustness and performance (achieving a stable purity of 0.9892 molar fraction) to reduce the effects of combined faults considering changes of trajectories, on the other hand, the discrete PID presents difficulties to reduce the effect of the ramp-type fault since the purity drops to 0.82 in molar fraction. The discrete FTC achieves to produce bioethanol (above 99% wt) with purity values that international fuel standards allow.

Morphotectonic Processes in Seismic Zones of Moderate Intensity, Argentina

This study deals with the neotectonic deformation in seismic zones of moderate intensity in some areas of the Sierras Pampeanas, Santa Bárbara System and Chaqueña Plain of Argentina. In the study region, the location of earthquakes of ≥ three, ≥ four, and ≥ six Richter magnitudes agree with the traces of regional faults, evidencing their neotectonic activity. Seismic energy is generally transmitted over inherited faults, such as in the Metan basin. Minor new faults occur in Quaternary terraced deposits,and others move, taking advantage of the Neogene sedimentary strata. The folds are generally buried, but the younger sequences are gently undulating. The seismic energy dissipated through fewer cohesion materials that form the valleys' fill, developing discrete fault scarps and strongly folded conglomerate strata. The foothills deposits and basins absorbed most of the seismic energy released during the reactivation of the faults. Tectonic activity is deforming 630 BP deposits in the Cumbres Calchaquíes piedmont. Considering deformation values, neotectonic deformation in the outcrops and seismic profiles evidence, it is possible to interpret that the seismic activity in the study area from the Pleistocene to the present remained between the current records. This seismic activity, sustained over time, is sufficient to produce deformation in the foothills, reactivate pre-existing faults with small displacements and generate minor new faults in recent conglomeratic deposits. Many faults are blind. However, the deformation of the landscape and the modification of the drainage network are direct indicators of the activity of these structures.

Back-arc suture zone along the north margin of the eastern Cimmerian continent

The Cimmerian continent is the north piece of the Gondwana super-continent collaged to the south edge of the Laurasia super-continent during the closure of the Paleo-Tehyan Ocean. Researchers recently have identified the Rushan-Pshart-Longmu Co-Shuanghu-Bitu-Changning-Menglian-Inthanon suture zone as the northern boundary of the eastern Cimmerian continent. However, a detailed correlation of this complicated tectonic zone from Pamir to Sumatra remains unclear. For example, while a back-arc suture is developed in southeast Tibet and Southeast Asia, no evidence of the same suture has been reported in eastern and central Tibet. In this study, we investigate an ophiolite mélange suite exposed in the Deqin back-arc suture of this tectonic zone in eastern Tibet, and interpret it as the northward extension of the Jinghong-Nan River back-arc suture. The mélange includes serpentinites, gabbros, basalts, and minor abysmal radiolarian-bearing cherts, and these rocks appear as isolated blocks in fault contact with Permian strata. Geochemical data of the serpentinites from the Deqin suture and Bitu suture indicate that they are MOR-type and SSZ-type sutures, respectively. Zircon UPb dating of the gabbro and diorite from the Deqin suture yields crystallization ages ranging from ca. 246 Ma to ca. 276 Ma, and a zircon UPb age of ca. 285 Ma is obtained from the Bitu suture. Geochemical analysis shows that the rocks from the Deqin suture have OIB or MORB characteristics, suggesting southwest subduction of the oceanic lithosphere beneath the North Lancangjiang tectonic belt since the Middle Permian. Two Meso-Tethyan magmatic rock samples from the Bitu and the Deqin sutures crystalized at 114 Ma and 111 Ma, respectively, and their geochemical data indicate OIB-type signature. We conclude that the Bangong Co-Nujiang Ocean lithosphere subducted northeastward beneath the Qamdo terrane at a low angle. Based on the correlation between the Rushan-Pshart suture and the Longmu Co-Shuanghu suture, our pre-Cenozoic plate reconstruction suggests that the Karakorum fault right-laterally offset the northern boundary of the Cimmerian continent by 140 ± 10 km. The offset further implies that the Cenozoic deformation of the Tibetan plateau is accommodated mainly by distributed structures rather than by several discrete fault systems.

Slip Deficit Rates on Southern Cascadia Faults Resolved with Viscoelastic Earthquake Cycle Modeling of Geodetic Deformation

ABSTRACT The fore-arc of the southern Cascadia subduction zone (CSZ), north of the Mendocino triple junction (MTJ), is home to a network of Quaternary-active crustal faults that accumulate strain due to the interaction of the North American, Juan de Fuca (Gorda), and Pacific plates. These faults, including the Little Salmon and Mad River fault (LSF and MRF) zones, are located near the most populated parts of California’s north coast and show paleoseismic evidence for three slip events of several-meter scale in the past 1700 yr. However, the geodetic slip rates of these faults are poorly constrained. In this work, we analyze a new compilation of interseismic geodetic velocities from Global Navigation Satellite Systems, leveling, and tide gauge data near the MTJ to constrain present-day slip deficit rates on upper-plate faults and coupling on the megathrust. We construct Green’s functions for interseismic slip deficit for discrete faults embedded in an elastic plate overlying a viscoelastic mantle. We then use a constrained least-squares inversion to determine best-fitting slip rates on the major faults and investigate slip rate trade-offs between faults. Results indicate that the LSF and MRF systems together accumulate 4–5 mm/yr of reverse-slip deficit, although their separate slip rates cannot be determined independently. Modeling of the horizontal and vertical velocities suggests that the southernmost CSZ is coupled interseismically to deeper than 25 km depth. We also find that 6–17 mm/yr of right-lateral slip deficit extends north of the MTJ and into the southern Cascadia fore-arc. These results reinforce the notion that both the southernmost Cascadia megathrust and the smaller fore-arc faults above it contribute to regional seismic hazard.

Cascading foreshocks, aftershocks and earthquake swarms in a discrete fault network

SUMMARY Earthquakes come in clusters formed of mostly aftershock sequences, swarms and occasional foreshock sequences. This clustering is thought to result either from stress transfer among faults, a process referred to as cascading, or from transient loading by aseismic slip (pre-slip, afterslip or slow slip events). The ETAS statistical model is often used to quantify the fraction of clustering due to stress transfer and to assess the eventual need for aseismic slip to explain foreshocks or swarms. Another popular model of clustering relies on the earthquake nucleation model derived from experimental rate-and-state friction. According to this model, earthquakes cluster because they are time-advanced by the stress change imparted by the mainshock. This model ignores stress interactions among aftershocks and cannot explain foreshocks or swarms in the absence of transient loading. Here, we analyse foreshock, swarm and aftershock sequences resulting from cascades in a Discrete Fault Network model governed by rate-and-state friction. We show that the model produces realistic swarms, foreshocks and aftershocks. The Omori law, characterizing the temporal decay of aftershocks, emerges in all simulations independently of the assumed initial condition. In our simulations, the Omori law results from the earthquake nucleation process due to rate and state friction and from the heterogeneous stress changes due to the coseismic stress transfers. By contrast, the inverse Omori law, which characterizes the accelerating rate of foreshocks, emerges only in the simulations with a dense enough fault system. A high-density complex fault zone favours fault interactions and the emergence of an accelerating sequence of foreshocks. Seismicity catalogues generated with our discrete fault network model can generally be fitted with the ETAS model but with some material differences. In the discrete fault network simulations, fault interactions are weaker in aftershock sequences because they occur in a broader zone of lower fault density and because of the depletion of critically stressed faults. The productivity of the cascading process is, therefore, significantly higher in foreshocks than in aftershocks if fault zone complexity is high. This effect is not captured by the ETAS model of fault interactions. It follows that a foreshock acceleration stronger than expected from ETAS statistics does not necessarily require aseismic slip preceding the mainshock (pre-slip). It can be a manifestation of a cascading process enhanced by the topological properties of the fault network. Similarly, earthquake swarms might not always imply transient loading by aseismic slip, as they can emerge from stress interactions.

A comparative analysis of continuum plasticity, viscoplasticity and phase-field models for earthquake sequence modeling

This paper discusses continuum models for simulating earthquake sequences on faults governed by rate-and-state dependent friction. Through detailed numerical analysis of a conventional strike-slip fault, new observations regarding the use of various continuum earthquake models are presented. We update a recently proposed plasticity-based model using a consistently linearized formulation, show its agreement with discrete fault models for fault thicknesses of hundreds of meters, and demonstrate mesh objectivity for slip-related variables. To obtain a fully regularized fault width description with an internal length scale, we study the performance and mesh convergence of a plasticity-based model complemented by a Kelvin viscosity term and the phase-field approach to cohesive fracture. The Kelvin viscoplasticity-based model can introduce an internal length scale and a mesh-objective response. However, on grid sizes down to meters, this only holds for very high Kelvin viscosities that inhibit seismic slip rates, which renders this approach impractical for simulating earthquake sequences. On the other hand, our phase-field implementation for earthquake sequences provides a numerically robust framework that agrees with a discrete reference solution, is mesh objective, and reaches seismic slip rates. The model, unsurprisingly, requires highly refined grids around the fault zones to reproduce results close to a discrete model. Following this line, the effect of an internal length scale parameter on the phase-field predictions and mesh convergence are discussed.

Old orogen – young topography: Evidence for relief rejuvenation in the Bohemian Massif

Abstract The Bohemian Massif is the relic of a major Paleozoic mountain range that is known to have exhumed and its surface levelled in the Permian, but its Neogene landscape evolution is largely unconstrained. The landscape is characterized by rolling hills and extended planation surfaces above an elevation of about 500 m. However, at lower elevations deeply incised gorges confined by steep hillslopes are abundant and contrast impressively with the low relief landscapes above. Rivers with a bimodal morphology (i.e. steep at lower elevations and gentle at higher elevations) drain either to the north into the Vltava (Moldau) River or to the south into the Danube River. Hence, a continental drainage divide runs through the Bohemian Massif. Here, we quantify spatial characteristics of the Bohemian Massif landforms by computing landscape metrics like steepness index or geophysical relief derived from digital elevation models. From this we infer temporal change of the landscape in the past and predict them for the future evolution of the region. We show that the landscape is characterized by out-of-equilibrium river profiles with knickpoints abundantly at elevations between 450 m and 550 m separating steep channel segments at lower elevations from less steep channels at higher elevations. Hypsometric maxima at or close above knickpoint elevations, along with high and low values in geophysical relief as indicator for the degree of fluvial landscape dissection downstream and upstream of major knickpoints, support the idea of landscape bimodality. Furthermore, we find a distinct drainage divide asymmetry, which causes the reorganization of the drainage network of the region. Across-divide gradients in channel steepness predict the northward migration of the Danube-Vltava drainage divide including growth and shrinkage of tributary catchments, thus controlling changes in the Central European drainage pattern. All aspects suggest that the region experienced relief rejuvenation during the last few million years. We suggest that this relief rejuvenation is related to the inversion of the Molasse basin with a long wavelength rock uplift pattern and low uplift rates. Vertical motion of crustal blocks at discrete faults may locally affect the uplift pattern. However, the contrasting bedrock properties between the sedimentary cover (Molasse sediments) and the crystalline basement (Bohemian Massif) cause substantial differences in erosion rate and are thus the superior control on the topographic variations of the entire region.

Fault tolerant time optimization for a class of time-varying switched infinite dimensional linear systems

This paper addresses the issue of finding the optimal switching times for the time-varying switched infinite dimensional linear system with discrete faults that lead to the deviation of the actual switching signal from the normal one. A robust fault tolerant time optimization scheme based on an equivalent time transformation and a min–max mechanism is proposed to obtain the upper bound of optimal values of cost functional of all possible discrete faults. For any detectable discrete fault, an active fault tolerant time optimization scheme equipped with a switching detection technique and a gradient descent algorithm is presented to minimize every post-fault cost functional, which reduces the conservation of the robust one.

Viscoelastic Fault-Based Model of Crustal Deformation for the 2023 Update to the U.S. National Seismic Hazard Model

Abstract The 2023 update to the National Seismic Hazard (NSHM) model is informed by several deformation models that furnish geodetically estimated fault slip rates. Here I describe a fault-based model that permits estimation of long-term slip rates on discrete faults and the distribution of off-fault moment release. It is based on quantification of the earthquake cycle on a viscoelastic model of the seismogenic upper crust and ductile lower crust and mantle. I apply it to a large dataset of horizontal and vertical Global Positioning System (GPS) interseismic velocities in the western United States, resulting in long-term slip rates on more than 1000 active faults defined for the NSHM. A reasonable fit to the GPS dataset is achieved with a set of slip rates designed to lie strictly within a priori geologic slip rate bounds. Time-dependent effects implemented via a “ghost transient” have a profound effect on slip rate estimation and tend to raise calculated slip rates along the northern and southern San Andreas fault by up to several mm/yr.

Relating Slip Behavior to Off‐Fault Deformation Using Physical Models

AbstractDeformation in transform systems is accommodated by discrete fault slip and distributed off‐fault deformation. Here, we consider how a change in slip behavior along a fault can influence the distribution between on‐ and off‐fault deformation. We use a physical experiment to simplify the geometry, material properties, boundary conditions, and slip history along a strike‐slip fault to directly observe patterns of off‐fault deformation. We document deformation of a silicone slab on a simple shear apparatus using particle image velocimetry (2D) and photogrammetry (3D). The experimental results show regions of topographic highs and lows on either side of the slip transition that grow, evolve, and are displaced with progressive strain. The experimental dilatation field shares similarities with strain fields in central California along the San Andreas fault, which suggests that a change in slip behavior may explain some of the real‐world patterns in short‐ and long‐term deformation.

How hydrocarbons move along faults: Evidence from microstructural observations of hydrocarbon-bearing carbonate fault rocks

The microscale mechanisms of hydrocarbons movement along faults and fault zones, the potential carriers of hydrocarbons toward the productive geological traps, remain largely unknown. The majority of previous studies inferred the hydraulic behavior of faults with respect to hydrocarbon movements without providing meso and microstructural observations from faults permeated by hydrocarbons. To fill this gap, we document meso-structures together with the first fossil microstructural portraits of hydrocarbon flow and pathways along two hydrocarbon-bearing carbonate-hosted normal faults exposed in the central Apennines, Italy. In particular, we show that hydrocarbons cyclically move within tectonically active carbonate normal faults possibly during interseismic and coseismic phases of the seismic cycle. Channelized structures, injection features, and clast-cortex grains suggest the occurrence of transient and localized pulses of pressurized hydrocarbons during coseismic slip. In particular, clast-cortex grains are very similar to microstructures that develop along fault planes for slip velocities between 0.0001 and 1 m/s. Patches of hydrocarbon-bearing breccias/cataclasites with lobate and irregular boundaries, crackle breccias filled by hydrocarbons, and hydrocarbons arrested against hydrocarbon-free discrete fault planes suggest hydrocarbon flow during the interseismic phases with hydrocarbon (over)pressure dissipation after coseismic phases. Fault permeability is created during the coseismic phase and hydrocarbons penetrate the most permeable and uncemented uncohesive fault rocks within the damage zone and arrest against and/or within low-permeability and cemented fault cores. Results are consistent with previous numerical simulations on hydrocarbon movements along faults and time-lapse seismic-reflection imaging, suggesting that the movement of hydrocarbon occurs during interseismic periods within tectonically active faults and along permeable zones cyclically created by seismic activity. Results from this paper are crucial for modelling the hydraulic behavior of carbonate fault damage zone, which have progressively gained popularity as targets of hydrocarbon exploration and production and for CO2 or H storage.

Contribution of the 2010 Maule Megathrust Earthquake to the Heat Flow at the Peru-Chile Trench

The 2010 Maule earthquake was a megathrust event that occurred along the Peru–Chile Trench. The earthquake source can be modelled as a fault with two asperities with different areas and strengths. By employing a discrete fault model, where asperities are the basic elements, the event can be described as a sequence of three dynamic modes involving simultaneous asperity slip. Interaction between asperities by mutual stress transfer plays a crucial role during fault slip. With a careful choice of values for the model parameters, the mode durations, the slip distribution, the seismic moment rate and the final moment calculated from the model are found to be consistent with the observed values. An important amount of frictional heat is produced by an event of this size and is calculated by summing up the contributions of each asperity. The seismic event produces a heat pulse propagating through the Earth’s crust and contributing to the average heat flow in the region. The calculated heat production is equal to about 2×1017 J and the peak value of the heat pulse is equal to 6×10−3 mW m−2 or about 10−4 of the average surface heat flow density, with a characteristic diffusion time in the order of 106 a.

Physical characterization of fault rocks within the Opalinus Clay formation

Near-surface disposal of radioactive waste in shales is a promising option to safeguard the population and environment. However, natural faults intersecting these geological formations can potentially affect the long-term isolation of the repositories. This paper characterizes the physical properties and mineralogy of the internal fault core structure intersecting the Opalinus Clay formation, a host rock under investigation for nuclear waste storage at the Mont Terri Laboratory (Switzerland). We have performed porosity, density, microstructural and mineralogical measurements in different sections of the fault, including intact clays, scaly clays and fault gouge. Mercury intrusion porosimetry analysis reveal a gouge that has a pore network dominated by nanopores of less than 10 nm, yet a high-porosity (21%) and low grain density (2.62 g/cm3) when compared to the intact rock (14.2%, and 2.69 g/cm3). Thus, a more permeable internal fault core structure with respect to the surrounding rock is deduced. Further, we describe the OPA fault gouge as a discrete fault structure having the potential to act as a preferential, yet narrow, and localized channel for fluid-flow if compared to the surrounding rock. Since the fault gouge is limited to a millimetres-thick structure, we expect the barrier property of the geological formation is almost not affected.

The role of thrust and strike-slip faults in controlling regional-scale paleofluid circulation in fold-and-thrust belts: Insights from the Jura Mountains (eastern France)

We combine structural and microstructural data with stable and clumped isotopes of syntectonic calcite veins or slickenfibers of five thrust and four strike-slip faults to characterize the paleofluid circulation in the Jura fold-and-thrust belt, eastern France. Syn-tectonic fluid circulation occurred along high permeability networks of breccias, foliated fault rocks, and discrete fault surfaces. At the regional scale, fluid circulation was dominated by cold meteoric fluids that infiltrated downward along both thrust and strike-slip faults, with various degrees of interaction with the carbonate host rocks. Fault-related mineralizations precipitated from fluids with δ⁠18O values between −0.8‰ and − 7.8‰ (V-SMOW) at temperatures between 8 °C and 54 °C. The δ⁠18O values of the paleofluids partly overlap those of modern meteoric waters of the region. The calcite mineralizations yielding the highest calculated δ⁠18O paleofluid values are also the warmest ones and those with the heaviest carbon isotope signal, indicating strong host rock buffering and fluid heating at depth. A contribution of deep fluids from Permo-Triassic rocks cannot be excluded, but not likely. This could be related to the presence of Middle Jurassic Opalinus Clay Formation, which acted as a regional low-permeability barrier in the sedimentary succession. This can create two different fluid circulation systems characterized by warm and partly basement-derived fluids and by cold meteoric fluids, respectively, below and above the Middle Jurassic Opalinus Clay Formation. Results from this study can be used for modeling fluid circulation at the regional scale in carbonate-dominant foreland fold-and-thrust belts elsewhere in the world.