An analysis of the factors that control fault zone architecture and the importance of fault orientation relative to regional stress

Abstract The moment magnitude 7.2 El Mayor–Cucapah (EMC) earthquake of 2010 in northern Baja California, Mexico produced a cascading rupture that propagated through a geometrically diverse network of intersecting faults. These faults have been exhumed from depths of 6–10 km since the late Miocene based on low-temperature thermochronology, synkinematic alteration, and deformational fabrics. Coseismic slip of 1–6 m of the EMC event was accommodated by fault zones that displayed the full spectrum of architectural styles, from simple narrow fault zones (< 100 m in width) that have a single high-strain core, to complex wide fault zones (> 100 m in width) that have multiple anastomosing high-strain cores. As fault zone complexity and width increase the full spectrum of observed widths (20–200 m), coseismic slip becomes more broadly distributed on a greater number of scarps that form wider arrays. Thus, the infinitesimal slip of the surface rupture of a single earthquake strongly replicates many of the fabric elements that were developed during the long-term history of slip on the faults at deeper levels of the seismogenic crust. We find that factors such as protolith, normal stress, and displacement, which control gouge production in laboratory experiments, also affect the architectural complexity of natural faults. Fault zones developed in phyllosilicate-rich metasedimentary gneiss are generally wider and more complex than those developed in quartzo-feldspathic granitoid rocks. We hypothesize that the overall weakness and low strength contrast of faults developed in phyllosilicate rich host rocks leads to strain hardening and formation of broad, multi-stranded fault zones. Fault orientation also strongly affects fault zone complexity, which we find to increase with decreasing fault dip. We attribute this to the higher resolved normal stresses on gently dipping faults assuming a uniform stress field compatible with this extensional tectonic setting. The conditions that permit slip on misoriented surfaces with high normal stress should also produce failure of more optimally oriented slip systems in the fault zone, promoting complex branching and development of multiple high-strain cores. Overall, we find that fault zone architecture need not be strongly affected by differences in the amount of cumulative slip and instead is more strongly controlled by protolith and relative normal stress.

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Permeability contrasts of fault zones - from conceptual model to numerical simulation

10.5194/egusphere-egu2020-6520 ◽

2020 ◽

Author(s):

Ulrich Kelka ◽

Thomas Poulet ◽

Luk Peeters

Keyword(s):

Fluid Flow ◽

Fault Zone ◽

Large Scale ◽

Regional Scale ◽

Damage Zone ◽

Fluid Pressure ◽

Fault Zones ◽

Strong Impact ◽

Fault Zone Architecture ◽

The Impact

Fault and fracture networks can govern fluid flow patterns in the subsurface and predicting fluid flow on a regional scale is of interest in a variety of fields like groundwater management, mining engineering, energy, and mineral resources. Especially the pore fluid pressure can have a strong impact on the strength of fault zones and might be one of the drivers for fault reactivation. Reliable simulations of the transient changes in fluid pressure need to account for the generic architecture of fault zones that comprises strong permeability contrast between the fault core and damage zone.Particularly, the distribution and connectivity of large-scale fault zones can have a strong impact on the flow field. Yet, modelling numerically such features in their full complexity remains challenging. Often faults zones are conceptualized as forming exclusively either barriers or conduits to fluid flow. However, a generic architecture of fault zones often comprises a discrete fault core surrounded by a diffuse damage zone and conceptualizing large scale discontinuities simply as a barrier or conduit is unlikely to capture the regional scale fluid flow dynamics. It is known that if the fault zone is hosted in low-permeability strata, such as clays or crystalline rocks, a transversal flow barrier can form along the fault core whereas the fracture-rich fault damage zone represents a longitudinal conduit. In more permeable host-rocks (i.e. sandstones or carbonates) the reverse situation can occur, and the permeability distributions in the damage zones can be governed by the abundance of low-permeability deformation features. A reliable numerical model needs to account for the difference and strong contrasts in fluid flow properties of the core and the damage zone, both transversally and longitudinally, in order to make prediction about the regional fluid flow pattern.Here, we present a numerical method that accounts for the generic fault zone architecture as lower dimensional interfaces in conforming meshes during fluid flow simulations in fault networks. With this method we aim to decipher the impact of fault zone architecture on subsurface flow pattern and fluid pressure evolution in fractures and faulted porous media. The method is implemented in a finite element framework for Multiphysics simulations. We demonstrate the impact of considering the more generic geological structure of individual faults on the flow field by conceptualizing discontinuities either as barriers, conduits or as a conduit-barrier system and show were these conceptualizations are applicable in natural systems. We further show that a reliable regional scale fluid flow simulation in faulted porous media needs to account for the generic fault zone architecture. The approach is finally used to evaluate the fluid flow response of statistically parameterised faulted media, in order to investigate the impact and sensitivity of each variable parameter.

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In-situ petrophysical and geomechanical characterization and 3D modelling of a mature normal fault zone (Goddo fault, Bømlo – Norway)

10.5194/egusphere-egu2020-6691 ◽

2020 ◽

Author(s):

Alberto Ceccato ◽

Giulio Viola ◽

Marco Antonellini ◽

Giulia Tartaglia ◽

Eric James Ryan

Keyword(s):

Mechanical Properties ◽

Structural Analysis ◽

Fault Zone ◽

Normal Fault ◽

Fault Zones ◽

Fault Rock ◽

Fracture Patterns ◽

Fault Zone Architecture

The detailed characterization of internal fault zone architecture and&#160; petrophysical and geomechanical properties of fault rocks is fundamental to understanding the flow and mechanical behaviour of mature fault zones. The Goddo normal fault (B&#248;mlo &#8211; Norway) accommodated c. E-W extension related to North Sea Rifting from Permian to Early Cretaceous times [1]. It represents a good example of a mature, iteratively reactivated and thus long-lived (seismogenic?) fault zone, developed in a pervasively fractured granitoid basement at upper crustal conditions in a regional extensional setting.Field characterization of the fault zone&#8217;s structural facies and analysis of background fracture patterns in the protolith have been integrated with in-situ petrophysical and geomechanical surveys of the recognized fault zone architectural components. In-situ air-permeability and mechanical directional tests (performed with NER TinyPerm III air-minipermeameter and DRC GeoHammer, L-type Schmidt hammer, respectively) have allowed for the quantification of the permeability tensor and mechanical properties (UCS and elastic modulus) within each brittle structural facies. Mechanical properties measured parallel to fault rock fabric of cataclasite- and gouge-bearing structural facies differ by up to one order of magnitude from those measured perpendicularly to it (~10 MPa vs. 100-200 MPa in UCS, respectively). Accordingly, permeability of cataclasite- and gouge-bearing facies is several orders of magnitude larger when measured parallel to fault-rock fabric than that perpendicular to it (10-0-10-1 D vs. 10-2-10-3 D, respectively). Virtual outcrop models (VOMs) of the fault zone were obtained from high-resolution UAV-photogrammetry. Field measurements of fracture orientations were used for calibration of the VOMs to construct a statistically robust fracture dataset. The results of VOMs structural analysis allowed for the quantification of fracture intensity and geometrical characteristics of mesoscopic fracture patterns within the different domains of the fault zone architecture.Results from field, VOMs structural analysis, and in-situ petrophysical investigations have been integrated into a realistic 3D fault zone model with the software 3DMove (Petex). This model can be used to investigate the influence of mesoscopic fracture patterns, related to either the fault zone or the background fracturing, on the hydro-mechanical behaviour of a mature fault zone. In addition, the evolution of the hydro-mechanical properties through time can be assessed by integrating the progressive development of brittle structural facies and fracture sets developed during the incremental strain and stress history into the model. This contribution proposes a geologically-constrained method to quantify the geometry of 3D fault zones, as a possible tool for models to be adopted in stress-strain analysis, hydraulic characterization and in the mechanical analysis of fault zones.[1] Viola, G., Scheiber, T., Fredin, O., Zwingmann, H., Margreth, A., & Knies, J. (2016). Deconvoluting complex structural histories archived in brittle fault zones. Nature communications, 7, 13448.

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Mineralogy and Geochemistry of Uraniferous Sandstones in Fault Zone at Wadi El Sahu Area, Southwestern Sinai, Egypt: Implications for Provenance, Weathering and Tectonic Setting

Acta Geologica Sinica - English Edition ◽

10.1111/1755-6724.14613 ◽

2020 ◽

Author(s):

Osama R. Sallam ◽

Hamed I. Mira ◽

Amira M. El Tohamy ◽

Abd Elhadi A. Abbas

Keyword(s):

Fault Zone ◽

Tectonic Setting ◽

Southwestern Sinai

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Evolution of Friction and Permeability in a Propped Fracture under Shear

Geofluids ◽

10.1155/2017/2063747 ◽

2017 ◽

Vol 2017 ◽

pp. 1-13 ◽

Cited By ~ 8

Author(s):

Fengshou Zhang ◽

Yi Fang ◽

Derek Elsworth ◽

Chaoyi Wang ◽

Xiaofeng Yang

Keyword(s):

Normal Stress ◽

Shear Loading ◽

Particle Crushing ◽

Normal Loading ◽

Fracture Surfaces ◽

Frictional Strength ◽

Transport Response ◽

Shear Slip ◽

High Normal Stress ◽

Proppant Embedment

We explore the evolution of friction and permeability of a propped fracture under shear. We examine the effects of normal stress, proppant thickness, proppant size, and fracture wall texture on the frictional and transport response of proppant packs confined between planar fracture surfaces. The proppant-absent and proppant-filled fractures show different frictional strength. For fractures with proppants, the frictional response is mainly controlled by the normal stress and proppant thickness. The depth of shearing-concurrent striations on fracture surfaces suggests that the magnitude of proppant embedment is controlled by the applied normal stress. Under high normal stress, the reduced friction implies that shear slip is more likely to occur on propped fractures in deeper reservoirs. The increase in the number of proppant layers, from monolayer to triple layers, significantly increases the friction of the propped fracture due to the interlocking of the particles and jamming. Permeability of the propped fracture is mainly controlled by the magnitude of the normal stress, the proppant thickness, and the proppant grain size. Permeability of the propped fracture decreases during shearing due to proppant particle crushing and related clogging. Proppants are prone to crushing if the shear loading evolves concurrently with the normal loading.

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Acadian strike-slip tectonics in the Gaspé region, Quebec Appalachians

Canadian Journal of Earth Sciences ◽

10.1139/e89-149 ◽

1989 ◽

Vol 26 (9) ◽

pp. 1764-1777 ◽

Cited By ~ 24

Author(s):

Michel Malo ◽

Jacques Béland

Keyword(s):

Middle Devonian ◽

High Strain ◽

Structural Features ◽

Fault Zones ◽

Strike Slip ◽

Structural Units ◽

Middle Ordovician ◽

Southern Margin ◽

Intense Deformation ◽

Dextral Strike Slip

At the southern margin of the Cambro-Ordovician Humber Zone in the Quebec Appalachians, on Gaspé Peninsula, three structural units of Middle Ordovician to Middle Devonian cover rocks of the Gaspé Belt are in large part bounded by long, straight longitudinal faults. In one of these units, the Aroostook–Percé anticlinorium, several structural features, which can be ascribed to Acadian deformation, are controlled by three subparallel, dextral, strike-slip longitudinal faults: Grande Rivière, Grand Pabos, and Rivière Garin. These faults follow bands of intense deformation, contrasting with the mildly to moderately deformed intervals that separate them.Most of the structural features observed – rotated oblique folds and cleavage, subsidiary Riedel and tension faults, and offsets of markers – can be integrated in a model of strike-slip tectonics that operated in ductile–brittle conditions. A late increment of deformation in the form of conjugate cleavages and minor faults is restricted to the bands of high strain. An anticlockwise transection of the synfolding cleavage in relation to the oblique hinges may be a feature of the rotational deformation.The combined dextral strike slip that can be measured within the three major longitudinal fault zones amounts to 138 km, to which can be added 17 km of ductile movement in the intervals, for a total of 155 km.

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Fault zone architecture and deformation processes within evaporitic rocks in the upper crust

Tectonics ◽

10.1029/2007tc002230 ◽

2008 ◽

Vol 27 (4) ◽

pp. n/a-n/a ◽

Cited By ~ 86

Author(s):

N. De Paola ◽

C. Collettini ◽

D. R. Faulkner ◽

F. Trippetta

Keyword(s):

Fault Zone ◽

Upper Crust ◽

Fault Zone Architecture ◽

Deformation Processes

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Carbonaceous Materials in the Fault Zone of the Longmenshan Fault Belt: 1. Signatures within the Deep Wenchuan Earthquake Fault Zone and Their Implications

Minerals ◽

10.3390/min8090385 ◽

2018 ◽

Vol 8 (9) ◽

pp. 385 ◽

Cited By ~ 4

Author(s):

Li-Wei Kuo ◽

Jyh-Rou Huang ◽

Jiann-Neng Fang ◽

Jialiang Si ◽

Haibing Li ◽

...

Keyword(s):

Wenchuan Earthquake ◽

Fault Zone ◽

Active Fault ◽

Carbonaceous Materials ◽

Coseismic Slip ◽

Earthquake Fault ◽

Active Fault Zone ◽

2008 Wenchuan Earthquake ◽

Seismic Slip ◽

Longmenshan Fault

Graphitization of carbonaceous materials (CM) has been experimentally demonstrated as potential evidence of seismic slip within a fault gouge. The southern segment of the Longmenshan fault, a CM-rich-gouge fault, accommodated coseismic slip during the 2008 Mw 7.9 Wenchuan earthquake and potentially preserves a record of processes that occurred on the fault during the slip event. Here, we present a multi-technique characterization of CM within the active fault zone of the Longmenshan fault from the Wenchuan earthquake Fault Scientific Drilling-1. By contrast with field observations, graphite is pervasively and only distributed in the gouge zone, while heterogeneously crystallized CM are present in the surrounding breccia. The composite dataset that is presented, which includes the localized graphite layer along the 2008 Wenchuan earthquake principal slip zone, demonstrates that graphite is widely distributed within the active fault zone. The widespread occurrence of graphite, a seismic slip indicator, reveals that surface rupturing events commonly occur along the Longmenshan fault and are characteristic of this tectonically active region.

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DETAIL GRAVITY PROFILE ACROSS SAN ANDREAS FAULT ZONE

Geophysics ◽

10.1190/1.1439868 ◽

1967 ◽

Vol 32 (2) ◽

pp. 297-301 ◽

Cited By ~ 2

Author(s):

S. N. Domenico

Keyword(s):

Fault Zone ◽

Mojave Desert ◽

San Andreas Fault ◽

Surface Expression ◽

Fault Zones ◽

Rock Masses ◽

San Andreas ◽

Major Fault ◽

Reduced Density ◽

Gravity Profile

A gravity profile was obtained from closely spaced readings along a traverse approximately nine miles in length across the San Andreas fault zone immediately south of Palmdale, California in the western Mojave Desert. Corrected gravity values show a slight but distinctive minimum associated with the fault zone which may be attributed to the reduced density of the shattered rock masses in the fault zone. The existence of this minimum suggests that major fault zones may be traced across terrain, on which surface expression of the fault does not exist, by successive profiles across the suspected position of the fault zone.

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Spatial variation in coda Q and stressing rate around the Atotsugawa fault zone in a high strain rate zone, central Japan

Earth Planets and Space ◽

10.5047/eps.2012.08.012 ◽

2013 ◽

Vol 65 (2) ◽

pp. 115-119 ◽

Cited By ~ 8

Author(s):

Yoshihiro Hiramatsu ◽

◽

Akihiro Sawada ◽

Yoritaka Yamauchi ◽

Shingo Ueyama ◽

...

Keyword(s):

High Strain Rate ◽

Strain Rate ◽

Spatial Variation ◽

Fault Zone ◽

High Strain ◽

Coda Q ◽

Central Japan ◽

Atotsugawa Fault ◽

Stressing Rate

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Heterogeneous stresses and deformation mechanisms at shallow crustal conditions, Hungaroa Fault Zone, Hikurangi Subduction Margin, New Zealand

10.5194/egusphere-egu2020-11961 ◽

2020 ◽

Author(s):

Carolyn Boulton ◽

Marcel Mizera ◽

Maartje Hamers ◽

Inigo Müller ◽

Martin Ziegler ◽

...

Keyword(s):

Friction Coefficient ◽

Fault Zone ◽

Mixed Mode ◽

Fluid Pressure ◽

Fault Zones ◽

Deformation Mechanisms ◽

Multiple Observations ◽

Calcite Veins ◽

Dynamic Recrystallisation ◽

Clumped Isotope

The Hungaroa Fault Zone (HFZ), an inactive thrust fault along the Hikurangi Subduction Margin, accommodated large displacements (~4&#8211;10 km) at the onset of subduction in the early Miocene. Within a 40 m-wide high-strain fault core, calcareous mudstones and marls display evidence for mixed-mode viscous flow and brittle fracture, including: discrete faults; extensional veins containing stretched calcite fibers; shear veins with calcite slickenfibers; calcite foliation-boudinage structures; calcite pressure fringes; dark dissolution seams; stylolites; embayed calcite grains; and an anastomosing phyllosilicate foliation.Multiple observations indicate a heterogeneous stress state within the fault core. Detailed optical and electron backscatter diffraction-based texture analysis of syntectonic calcite veins and isoclinally folded limestone layers within the fault core reveal that calcite grains have experienced intracrystalline plasticity and interface mobility, and local subgrain development and dynamic recrystallisation. The recrystallized grain size in two calcite veins of 6.0&#177;3.9 &#181;m (n=1339; 1SD; HFZ-H4-5.2m_A;) and 7.2&#177;4.2&#181;m (n=406; 1SD; HFZ-H4-19.9m) indicate high differential stresses (~76&#8211;134 MPa). Hydrothermal friction experiments on a foliated, calcareous mudstone yield a friction coefficient of &#956;&#8776;0.35. Using this friction coefficient in the Mohr-Coulomb failure criterion yields a maximum differential stress of 55 MPa at 4 km depth, assuming a minimum principal stress equal to the vertical stress, an average sediment density of 2350 kg/m3, and hydrostatic pore fluid pressure. Interestingly, calcareous microfossils within the foliated mudstone matrix are undeformed. Moreover, calcite veins are oriented both parallel to and highly oblique to the foliation, indicating spatial and/or temporal variations in the maximum principle stress azimuth.To further constrain HFZ deformation conditions, clumped isotope geothermometry was performed on six syntectonic calcite veins, yielding formation temperatures of 79.3&#177;19.9&#176;C (95% confidence interval). These temperatures are well below those at which dynamic recrystallisation of calcite is anticipated and exclude shear heating and the migration of hotter &#64258;uids as an explanation for dynamic recrystallisation of calcite at shallow crustal levels (<5 km depth).Our results indicate that: (1) stresses are spatiotemporally heterogeneous in crustal fault zones containing mixtures of competent and incompetent minerals; (2) heterogeneous deformation mechanisms, including frictional sliding, pressure solution, dynamic recrystallization, and mixed-mode fracturing accommodate slip in shallow crustal fault zones; and (3) brittle fractures play a pivotal role in fault zone deformation by providing fluid pathways that promote fluid-enhanced recovery and dynamic recrystallisation in the deforming calcite at remarkably low temperatures. Together, field geology, microscopy, and clumped isotope geothermometry provide a powerful method for constraining the multiscale slip behavior of large-displacement fault zones.

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