Episodic fluid flow in an active fault

Abstract We present a reconstruction of episodic fluid flow over the past ∼250 k.y. along the Malpais normal fault, which hosts the Beowawe hydrothermal system (Nevada, USA), using a novel combination of the apatite (U-Th)/He (AHe) thermochronometer and a model of the thermal effects of fluid flow. Samples show partial resetting of the AHe thermochronometer in a 40-m-wide zone around the fault. Numerical models using current fluid temperatures and discharge rates indicate that fluid flow events lasting 2 k.y. or more lead to fully reset samples. Episodic fluid pulses lasting 1 k.y. result in partially reset samples, with 30–40 individual fluid pulses required to match the data. Episodic fluid flow is also supported by an overturned geothermal gradient in a borehole that crosses the fault, and by breaks in stable isotope trends in hydrothermal sinter deposits that coincide with two independently dated earthquakes in the past 20 k.y. This suggests a system where fluid flow is triggered by repeated seismic activity, and that seals itself over ∼1 k.y. due to the formation of clays and silicates in the fault damage zone. Hydrothermal activity is younger than the 6–10 Ma age of the fault, which means that deep (∼5 km) fluid flow was initiated only after a large part of the 230 m of fault offset had taken place.

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Thermochronology and REE analyses as new tools to track thermal anomaly and fluid flow along a crustal scale fault (Têt fault, French Pyrenees)

10.5194/egusphere-egu2020-8850 ◽

2020 ◽

Author(s):

Gaétan Milesi ◽

Monié Patrick ◽

Philippe Münch ◽

Roger Soliva ◽

Sylvain Mayolle ◽

...

Keyword(s):

Numerical Modelling ◽

Hot Springs ◽

Hot Spring ◽

Numerical Models ◽

Hanging Wall ◽

Damage Zone ◽

Thermal Anomaly ◽

Geothermal Gradient ◽

Fault Damage Zone ◽

Hydrothermal Flow

The T&#234;t fault is a crustal scale major fault in the eastern Pyrenees that displays about 30 hot springs along its surface trace with temperatures between 29&#176;C and 73&#176;C. The regional process of fluid circulation at depth has previously been highlighted by thermal numerical modelling supported by hydrochemical analyses and tectonic study. Numerical modelling suggests the presence of a strong subsurface anomaly of temperature along-fault (locally > 90&#176;C/km), governed by topography-driven meteoric fluid upflow through the fault damage zone (advection). On the basis of this modelling, we focused our thermochronological study on 30 samples collected close and between two hot spring clusters in both the hanging wall and the footwall of the T&#234;t fault, where the most important thermal anomaly is recorded by models. We analysed apatite using (U-Th)/He (AHe) dating combined with REE analyses on the same dated grains.Along the fault, AHe ages are in a range of 26 to 8 Ma in the footwall and 43 and 18 Ma in the hanging wall, and only few apatite grains have been impacted by hydrothermalism near the St-Thomas hot spring cluster. By contrast, particularly young AHe ages below 6 Ma, correlated to REE depletion, are found around the Thu&#232;s-les-bains hot spring cluster. These very young ages are therefore interpreted as thermal resetting due to an important hydrothermal activity. A thermal anomaly can be mapped and appears restricted to 1 km around this cluster of hot springs, i.e. more restricted than the size of the anomaly predicted by numerical models. These results reveal that AHe dating and REE analyses can be used to highlight neo- or paleo-hydrothermal anomaly recorded by rocks along faults.This study brings new elements to discuss the onset of the hydrothermal circulations and consequences on AHe and REE mobilisation, and suggest a strong heterogeneity of the hydrothermal flow pattern into the fault damage zone. Moreover, this study suggests that crustal scale faults adjacent to reliefs can localise narrow high hydrothermal flow and important geothermal gradient.&#160;&#160;Besides these results, this study provides new constraints for geothermal exploration around crustal faults, as well as a discussion on the use of thermochronometers into fault damage zones.&#160;

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Geophysical characterisation of two segments of the Møre-Trøndelag Fault Complex, Mid-Norway

Solid Earth Discussions ◽

10.5194/sed-3-159-2011 ◽

2011 ◽

Vol 3 (1) ◽

pp. 159-186

Author(s):

A. Nasuti ◽

C. Pascal ◽

J. Ebbing ◽

J. F. Tønnesen

Keyword(s):

Tectonic Evolution ◽

Deep Structure ◽

Normal Fault ◽

Geophysical Data ◽

Data Sets ◽

Normal Faulting ◽

The South ◽

The Past ◽

Magnetic Resistivity ◽

Wide Zone

Abstract. The Møre-Trøndelag Fault Complex (MTFC) has controlled the tectonic evolution of Mid-Norway and its shelf for the past 400 Myr through repeated reactivations during Paleozoic, Mesozoic and perhaps Cenozoic times, the very last phase of reactivation involving normal to oblique slip faulting. Despite its pronounced signature in the landscape, its deep structure has remained unresolved until now. We focused on two specific segments of the MTFC (i.e. the so-called "Tjellefonna" and "Bæverdalen" faults) and acquired multiple geophysical data sets (i.e. gravity, magnetic, resistivity and shallow refraction profiles). A 100–200 m wide zone of gouge and/or brecciated bedrock dipping steeply to the south is interpreted as being the "Tjellefonna Fault" stricto sensu. The fault appears to be flanked by two additional but minor damage zones. A secondary normal fault also steeply dipping to the south but involving indurated breccias was detected ~1 km farther north. The "Bæverdalen Fault" is interpreted as a ~700 m wide and highly deformed zone involving fault gouge, breccias and lenses of intact bedrock, as such it is probably the most important fault segment in the studied area and accommodated most of the strain during presumably late Jurassic normal faulting. Our geophysical data are indicative of a "Bæverdalen Fault" dipping steeply towards the south, in agreement with the average orientation of the local tectonic grain. Our findings suggest that the influence of Mesozoic normal faulting along the MTFC on landscape development is more complex than previously anticipated.

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Signature of transition to supershear rupture speed in the coseismic off-fault damage zone

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2021.0364 ◽

2021 ◽

Vol 477 (2255) ◽

Author(s):

Jorge Jara ◽

Lucile Bruhat ◽

Marion Y. Thomas ◽

Solène L. Antoine ◽

Kurama Okubo ◽

...

Keyword(s):

High Resolution ◽

Fracture Mechanics ◽

Shear Wave Velocity ◽

Observational Studies ◽

Numerical Models ◽

Damage Zone ◽

Precise Location ◽

Earthquake Ruptures ◽

Fault Damage Zone ◽

Rupture Speed

Most earthquake ruptures propagate at speeds below the shear wave velocity within the crust, but in some rare cases, ruptures reach supershear speeds. The physics underlying the transition of natural subshear earthquakes to supershear ones is currently not fully understood. Most observational studies of supershear earthquakes have focused on determining which fault segments sustain fully grown supershear ruptures. Experimentally cross-validated numerical models have identified some of the key ingredients required to trigger a transition to supershear speed. However, the conditions for such a transition in nature are still unclear, including the precise location of this transition. In this work, we provide theoretical and numerical insights to identify the precise location of such a transition in nature. We use fracture mechanics arguments with multiple numerical models to identify the signature of supershear transition in coseismic off-fault damage. We then cross-validate this signature with high-resolution observations of fault zone width and early aftershock distributions. We confirm that the location of the transition from subshear to supershear speed is characterized by a decrease in the width of the coseismic off-fault damage zone. We thus help refine the precise location of such a transition for natural supershear earthquakes.

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Monitoring the response of volcanic CO2 emissions to changes in the Los Humeros hydrothermal system

Scientific Reports ◽

10.1038/s41598-021-97023-x ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Anna Jentsch ◽

Walter Duesing ◽

Egbert Jolie ◽

Martin Zimmer

Keyword(s):

Fluid Flow ◽

Hydrothermal System ◽

Damage Zone ◽

Inverse Correlation ◽

Normal Fault ◽

Atmospheric Effects ◽

Volcanic Complex ◽

Geothermal Resources ◽

Gas Emissions ◽

Soil Degassing

AbstractCarbon dioxide is the most abundant, non-condensable gas in volcanic systems, released into the atmosphere through either diffuse or advective fluid flow. The emission of substantial amounts of CO2 at Earth’s surface is not only controlled by volcanic plumes during periods of eruptive activity or fumaroles, but also by soil degassing along permeable structures in the subsurface. Monitoring of these processes is of utmost importance for volcanic hazard analyses, and is also relevant for managing geothermal resources. Fluid-bearing faults are key elements of economic value for geothermal power generation. Here, we describe for the first time how sensitively and quickly natural gas emissions react to changes within a deep hydrothermal system due to geothermal fluid reinjection. For this purpose, we deployed an automated, multi-chamber CO2 flux monitoring system within the damage zone of a deep-rooted major normal fault in the Los Humeros Volcanic Complex (LHVC) in Mexico and recorded data over a period of five months. After removing the atmospheric effects on variations in CO2 flux, we calculated correlation coefficients between residual CO2 emissions and reinjection rates, identifying an inverse correlation of ρ = − 0.51 to − 0.66. Our results indicate that gas emissions respond to changes in reinjection rates within 24 h, proving an active hydraulic communication between the hydrothermal system and Earth’s surface. This finding is a promising indication not only for geothermal reservoir monitoring but also for advanced long-term volcanic risk analysis. Response times allow for estimation of fluid migration velocities, which is a key constraint for conceptual and numerical modelling of fluid flow in fracture-dominated systems.

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Deformation band populations in fault damage zone—impact on fluid flow

Computational Geosciences ◽

10.1007/s10596-009-9148-8 ◽

2009 ◽

Vol 14 (2) ◽

pp. 231-248 ◽

Cited By ~ 11

Author(s):

Dmitry Kolyukhin ◽

Sylvie Schueller ◽

Magne S. Espedal ◽

Haakon Fossen

Keyword(s):

Fluid Flow ◽

Deformation Band ◽

Damage Zone ◽

Fault Damage Zone

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Fault damage zone volume and initial salinity distribution determine intensity of shallow aquifer salinisation in subsurface storage

Hydrology and Earth System Sciences ◽

10.5194/hess-20-1049-2016 ◽

2016 ◽

Vol 20 (3) ◽

pp. 1049-1067 ◽

Cited By ~ 10

Author(s):

Elena Tillner ◽

Maria Langer ◽

Thomas Kempka ◽

Michael Kühn

Keyword(s):

Fluid Flow ◽

Boundary Conditions ◽

Groundwater Resources ◽

Damage Zone ◽

Shallow Aquifer ◽

Scale Model ◽

Exclusion Criterion ◽

Salinity Distribution ◽

Fluid Displacement ◽

Fault Damage Zone

Abstract. Injection of fluids into deep saline aquifers causes a pore pressure increase in the storage formation, and thus displacement of resident brine. Via hydraulically conductive faults, brine may migrate upwards into shallower aquifers and lead to unwanted salinisation of potable groundwater resources. In the present study, we investigated different scenarios for a potential storage site in the Northeast German Basin using a three-dimensional (3-D) regional-scale model that includes four major fault zones. The focus was on assessing the impact of fault length and the effect of a secondary reservoir above the storage formation, as well as model boundary conditions and initial salinity distribution on the potential salinisation of shallow groundwater resources. We employed numerical simulations of brine injection as a representative fluid. Our simulation results demonstrate that the lateral model boundary settings and the effective fault damage zone volume have the greatest influence on pressure build-up and development within the reservoir, and thus intensity and duration of fluid flow through the faults. Higher vertical pressure gradients for short fault segments or a small effective fault damage zone volume result in the highest salinisation potential due to a larger vertical fault height affected by fluid displacement. Consequently, it has a strong impact on the degree of shallow aquifer salinisation, whether a gradient in salinity exists or the saltwater–freshwater interface lies below the fluid displacement depth in the faults. A small effective fault damage zone volume or low fault permeability further extend the duration of fluid flow, which can persist for several tens to hundreds of years, if the reservoir is laterally confined. Laterally open reservoir boundaries, large effective fault damage zone volumes and intermediate reservoirs significantly reduce vertical brine migration and the potential of freshwater salinisation because the origin depth of displaced brine is located only a few decametres below the shallow aquifer in maximum. The present study demonstrates that the existence of hydraulically conductive faults is not necessarily an exclusion criterion for potential injection sites, because salinisation of shallower aquifers strongly depends on initial salinity distribution, location of hydraulically conductive faults and their effective damage zone volumes as well as geological boundary conditions.

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Simulation of brine migration along geological fault zones using a consistent mesh approach

10.5194/egusphere-egu2020-7023 ◽

2020 ◽

Author(s):

Falko Vehling ◽

Firdovsi Gasanzade ◽

Jens-Olaf Delfs ◽

Sebastian Bauer

Keyword(s):

Fluid Flow ◽

Corner Point ◽

Fault Plane ◽

Damage Zone ◽

Gas Injection ◽

Gas Storage ◽

Fault Zones ◽

Formation Pressure ◽

Brine Migration ◽

Fault Damage Zone

Upward brine migration through permeable fault damage zones could endanger near-surface drinking water resources. Deep porous rock formations offer a large potential for gas storage, like e.g. methane or CO2. But gas injection induces formation pressure build up, that can potentially lead to vertical or horizontal brine displacement. Here fault zones play an important role as they can act either as lateral no-flow boundaries or as permeable pathways, that allow for fluid flow and pressure dissipation. Numerical reservoir simulations, which have become an important tool for investigating these effects quantitatively, have to be performed on a regional scale, in order to include the large-scale geological faults zones. Fault zones have to be implemented into the model in a geometrically and hydraulically flexible way, to account for the variety of natural conditions encountered, as e.g. open or closed fault zone.In order to model that complexity, the corner point grid approach has been applied by geologists for decades. The corner point grid utilizes a set of hexahedral blocks to represent geological formations. At the fault plane, where geological layers are vertically shifted, hanging nodes appear and the corner point grid cannot be used directly, if permeable fault zones have to be represented in the model. In this study we present an extension of a mesh converter, which removes hanging nodes at the fault plane by point combination, thus providing a consistent finite element mesh. Our numerical model can account for heterogeneous hydraulic properties of the fault damage zone and the enclosed fault core. The fault core is represented by one layer of 3D finite elements on each side of the fault plane. The fault damage zone consists of a continuous layer of quadrangular 2D finite elements, which are attached at the outer face of the 3D fault core elements. This model allows for fluid flow along the fault plane while fluid flow through the fault core could be adjusted by element permeability. This concept was implemented into a workflow using the FEM-simulator OpenGeoSys in combination with a mesh converter.The concept and workflow are shown to run stable using dedicated test cases for method validation, accounting for the coupled transport of water, heat and salt mass for different fault zone setups in a synthetic multi-layered subsurface. Here we focused on brine displacement and uprising due to formation pressure increase after gas injection, which is numerically realized by Dirichlet pressure boundary conditions. Further, we will investigate the relation between computational efficiency and flow solution differences by comparing this concept with the approach of fully discretized faults. Additionally, we will apply our workflow on a real geological case in the Northern German Basin, where a fault system is close to a potential gas storage side. &#160;

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Nonlinear fault damage zone scaling revealed through analog modeling

Geology ◽

10.1130/g48760.1 ◽

2021 ◽

Author(s):

Sylvain Mayolle ◽

Roger Soliva ◽

Stéphane Dominguez ◽

Christopher Wibberley ◽

Yannick Caniven

Keyword(s):

Failure Modes ◽

Damage Zone ◽

Normal Fault ◽

Fault Segment ◽

Mechanical Unit ◽

Analog Modeling ◽

Fault Damage Zone ◽

Fault Growth ◽

Fault Displacement ◽

Zone Growth

Fault damage zones strongly influence fluid flow and seismogenic behavior of faults and are thought to scale linearly with fault displacement until reaching a threshold thickness. Using analog modeling with different frictional layer thicknesses, we investigate damage zone dynamic evolution during normal fault growth. We show that experimental damage zone growth with displacement is not linear but progressively tends toward a threshold thickness, being larger in the thicker models. This threshold thickness increases significantly at fault segment relay zones. As the thickness threshold is approached, the failure mode progressively transitions from dilational shear to isochoric shear. This process affects the whole layer thickness and develops as a consequence of fault segment linkage as inferred in nature when the fault matures. These findings suggest that fault damage zone widths are limited both by different scales of mechanical unit thickness and the evolution of failure modes, ultimately controlled in nature by lithology and deformation conditions.

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Spatiotemporal history of fault–fluid interaction in the Hurricane fault, western USA

Solid Earth ◽

10.5194/se-11-1969-2020 ◽

2020 ◽

Vol 11 (6) ◽

pp. 1969-1985

Author(s):

Jace M. Koger ◽

Dennis L. Newell

Keyword(s):

Damage Zone ◽

Carbon Sources ◽

Normal Fault ◽

Western Usa ◽

Calcite Vein ◽

Regional Flow ◽

Fault Strength ◽

History Of ◽

Fault Damage Zone ◽

Fluid Interaction

Abstract. The Hurricane fault is a ∼250 km long, west-dipping, segmented normal fault zone located along the transition between the Colorado Plateau and the Basin and Range tectonic provinces in the western USA. Extensive evidence of fault–fluid interaction includes calcite mineralization and veining. Calcite vein carbon (δ13CVPDB) and oxygen (δ18OVPDB) stable isotope ratios range from −4.5 ‰ to 3.8 ‰ and from −22.1 ‰ to −1.1 ‰, respectively. Fluid inclusion microthermometry constrains paleofluid temperatures and salinities from 45 to 160 ∘C and from 1.4 wt % to 11.0 wt % as NaCl, respectively. These data suggest mixing between two primary fluid sources, including infiltrating meteoric water (70±10 ∘C, ∼1.5 wt % NaCl, δ18OVSMOW ∼-10 ‰) and sedimentary brine (100±25 ∘C, ∼11 wt % NaCl, δ18OVSMOW ∼ 5 ‰). Interpreted carbon sources include crustal- or magmatic-derived CO2, carbonate bedrock, and hydrocarbons. Uranium–thorium (U–Th) dates from five calcite vein samples indicate punctuated fluid flow and fracture healing at 539±10.8 (1σ), 287.9±5.8, 86.2±1.7, and 86.0±0.2 ka in the upper 500 m of the crust. Collectively, data predominantly from the footwall damage zone imply that the Hurricane fault imparts a strong influence on the regional flow of crustal fluids and that the formation of veins in the shallow parts of the fault damage zone has important implications for the evolution of fault strength and permeability.

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Spatiotemporal history of fluid-fault interaction in the Hurricane fault zone, western USA

10.5194/se-2020-69 ◽

2020 ◽

Author(s):

Jace M. Koger ◽

Dennis L. Newell

Keyword(s):

Damage Zone ◽

Carbon Sources ◽

Normal Fault ◽

Fault Interaction ◽

Calcite Vein ◽

Regional Flow ◽

Fault Strength ◽

Primary Fluid ◽

History Of ◽

Fault Damage Zone

Abstract. The Hurricane Fault is a ~250-km-long, west-dipping normal fault located along the transition between the Colorado Plateau and Basin and Range tectonic provinces in the western U.S. Extensive evidence of fluid-fault interaction, including calcite mineralization and veining, occur in the footwall damage zone. Calcite vein carbon (δ13CVPDB) and oxygen (δ18OVPDB) stable isotope ratios range from −4.5 to 3.8 ‰ and −22.1 to −1.1 ‰, respectively. Fluid inclusion microthermometry constrain paleofluid temperatures and salinities from 45–160 °C and 1.4–11.0 wt % as NaCl, respectively. These data identify mixing between two primary fluid sources including infiltrating meteoric groundwater (70 ± 10 °C, ~1.5 wt % NaCl, δ18OSMOW ~−10 ‰) and sedimentary brine (100 ± 25 °C, ~11 wt % NaCl, δ18OSMOW ~5 ‰). Interpreted carbon sources include crustal- or magmatic-derived CO2, carbonate bedrock, and hydrocarbons. U-Th dates from 5 calcite vein samples indicates punctuated fluid-flow and fracture healing at 539 ± 10.8, 287.9 ± 5.8, 86.2 ± 1.7, and 86.0 ± 0.2 ka in the upper 300 m of the crust. Collectively, the data imply that the Hurricane Fault imparts a strong influence on regional flow of crustal fluids, and that the formation of veins in the shallow parts of the fault damage zone has important implications for the evolution of fault strength and permeability.

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