scholarly journals From soft sediment deformation to fluid assisted faulting in the shallow part of a subduction megathrust analogue: the Sestola Vidiciatico tectonic Unit (Northern Apennines, Italy)

2017 ◽  
Vol 155 (2) ◽  
pp. 438-450 ◽  
Author(s):  
SILVIA MITTEMPERGHER ◽  
ANNA CERCHIARI ◽  
FRANCESCA REMITTI ◽  
ANDREA FESTA
Keyword(s):  
Fault Zone ◽  
Fluid Pressure ◽  
Shallow Depth ◽  
Seismogenic Zone ◽  
Burial Depth ◽  
Tectonic Unit ◽  
Multi Scale ◽  
High Fluid ◽  
Sediment Deformation ◽  
Last Stage

AbstractThe Sestola Vidiciatico tectonic Unit (SVU) accommodated the early Miocene convergence between the subducting Adriatic plate and the overriding Ligurian prism, and has been interpreted as a field analogue for the shallow portion of subduction megathrusts. The SVU incorporated sediments shortly after their deposition and was active down to burial depth corresponding to temperatures around 150 °C. Here, we describe the internal architecture of the basal thrust fault of the SVU through a multi-scale structural analysis and investigate the evolution of the deformation mechanisms with increasing burial depth. At shallow depth, the thrust developed in poorly lithified sediments which deformed by particulate flow. With increasing depth and lithification of sediments, deformation was accommodated in a meter scale, heterogeneous fault zone, including multiple strands of crack-and-seal shear veins, associated with minor distributed shearing in clay-rich domains and pressure solution. In the last stage, slip localized along a sharp, 20 cm thick shear vein, deactivating the fault zone towards the footwall. The widespread formation of crack-and-seal shear veins since the first stages of lithification indicates that failure along the thrust occurred at high fluid pressure and low differential stress already at shallow depth. Progressive shear localization occurs in the last phases of deformation, at temperatures typical of the transition to the seismogenic zone in active megathrusts.

Effects of heterogeneity on frictional-viscous deformation and the depth-extent of the seismogenic zone

2021 ◽  
Author(s):  
Ake Fagereng ◽  
Adam Beall
Keyword(s):  
Shear Stress ◽  
Yield Strength ◽  
Fault Zone ◽  
Fluid Pressure ◽  
Local Stress ◽  
Seismogenic Zone ◽  
Depth Range ◽  
Viscous Deformation ◽  
Viscosity Contrast ◽  
Depth Extent

<p>Current conceptual fault models define a seismogenic zone, where earthquakes nucleate, characterised by velocity-weakening fault rocks in a dominantly frictional regime. The base of the seismogenic zone is commonly inferred to coincide with a thermally controlled onset of velocity-strengthening slip or distributed viscous deformation. The top of the seismogenic zone may be determined by low-temperature diagenetic processes and the state of consolidation and alteration. Overall, the seismogenic zone is therefore described as bounded by transitions in frictional and rheological properties. These properties are relatively well-determined for monomineralic systems and simple, planar geometries; but, many exceptions, including deep earthquakes, slow slip, and shallow creep, imply processes involving compositional, structural, or environmental heterogeneities. We explore how such heterogeneities may alter the extent of the seismogenic zone.</p><p> </p><p>We consider mixed viscous-frictional deformation and suggest a simple rule of thumb to estimate the role of heterogeneities by a combination of the viscosity contrast within the fault, and the ratio between the bulk shear stress and the yield strength of the strongest fault zone component. In this model, slip behaviour can change dynamically in response to stress and strength variations with depth and time. We quantify the model numerically, and illustrate the idea with a few field-based examples: 1) earthquakes within the viscous regime, deeper than the thermally-controlled seismogenic zone, can be triggered by an increase in the ratio of shear stress to yield strength, either by increased fluid pressure or increased local stress; 2) there is commonly a depth range of transitional behaviour at the base of the seismogenic zone – the thickness of this zone increases markedly with increased viscosity contrast within the fault zone; and 3) fault zone weakening by phyllosilicate growth and foliation development increases viscosity ratio and decreases bulk shear stress, leading to efficient, stable, fault zone creep. These examples are not new interpretations or observations, but given the substantial complexity of heterogeneous fault zones, we suggest that a simplified, conceptual model based on basic strength and stress parameters is useful in describing and assessing the effect of heterogeneities on fault slip behaviour.         </p>

scholarly journals Fault valving and pore pressure evolution in simulations of earthquake sequences and aseismic slip

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Weiqiang Zhu ◽  
Kali L. Allison ◽  
Eric M. Dunham ◽  
Yuyun Yang
Keyword(s):  
Fault Zone ◽  
Fluid Pressure ◽  
Seismogenic Zone ◽  
Permeability Evolution ◽  
Aseismic Slip ◽  
Effective Normal Stress ◽  
Pressure Stress ◽  
Cyclic Changes ◽  
Earthquake Sequences ◽  
Pressure Evolution

Abstract Fault-zone fluids control effective normal stress and fault strength. While most earthquake models assume a fixed pore fluid pressure distribution, geologists have documented fault valving behavior, that is, cyclic changes in pressure and unsteady fluid migration along faults. Here we quantify fault valving through 2-D antiplane shear simulations of earthquake sequences on a strike-slip fault with rate-and-state friction, upward Darcy flow along a permeable fault zone, and permeability evolution. Fluid overpressure develops during the interseismic period, when healing/sealing reduces fault permeability, and is released after earthquakes enhance permeability. Coupling between fluid flow, permeability and pressure evolution, and slip produces fluid-driven aseismic slip near the base of the seismogenic zone and earthquake swarms within the seismogenic zone, as ascending fluids pressurize and weaken the fault. This model might explain observations of late interseismic fault unlocking, slow slip and creep transients, swarm seismicity, and rapid pressure/stress transmission in induced seismicity sequences.

scholarly journals Emplacement and biodegradation of oil in fractured basement: the ‘coal’ deposit in Moinian gneiss at Castle Leod, Ross-shire

2016 ◽  
Vol 107 (1) ◽  
pp. 23-32 ◽  
Author(s):  
John Parnell ◽  
Mas'ud Baba ◽  
Stephen Bowden
Keyword(s):  
Lower Devonian ◽  
Fluid Pressure ◽  
Low Permeability ◽  
Coal Deposit ◽  
Basin Inversion ◽  
Mineral Phases ◽  
Metamorphic Basement ◽  
Major Fault ◽  
High Fluid ◽  
Transfer Faults

ABSTRACTBitumen veins were formerly mined as ‘coal’ from Moinian metamorphic basement at Castle Leod, Strathpeffer, Ross-shire. The abundance and spatial concentration of hydrocarbons implies generation of a large volume of oil that exerted a fluid pressure great enough to open veins to 1+ m width. Biomarker characteristics, including β-carotane and a high proportion of C28 steranes, correlate the bitumen to Lower Devonian non-marine shales separated from the Moinian basement by a major fault. Bitumen in the Moinian basement has higher diasterane/sterane ratios than bitumen in the Devonian sequence, indicating greater levels of biodegradation, which may reflect more interaction with water in the basement. Replacive bitumen nodules in the Moinian basement, containing thoriferous/uraniferous mineral phases, are comparable with bitumen nodules in basement terrains elsewhere. Formation of the nodules represents hydrocarbon penetration of low-permeability basement, consistent with high fluid pressure. Bitumen veins are particularly orientated E–W, and may be associated with E–W transfer faults attributed to Permo-Carboniferous basin inversion.

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

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

<p>The Hungaroa Fault Zone (HFZ), an inactive thrust fault along the Hikurangi Subduction Margin, accommodated large displacements (~4–10 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.</p><p>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±3.9 µm (n=1339; 1SD; HFZ-H4-5.2m_A;) and 7.2±4.2µm (n=406; 1SD; HFZ-H4-19.9m) indicate high differential stresses (~76–134 MPa). Hydrothermal friction experiments on a foliated, calcareous mudstone yield a friction coefficient of μ≈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/m<sup>3</sup>, 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.</p><p>To further constrain HFZ deformation conditions, clumped isotope geothermometry was performed on six syntectonic calcite veins, yielding formation temperatures of 79.3±19.9°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 fluids as an explanation for dynamic recrystallisation of calcite at shallow crustal levels (<5 km depth).</p><p>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.</p>

MULTI-SCALE MECHANICAL BEHAVIOR ANALYSIS ON FLUID–SOLID COUPLING FOR OSTEONS IN VARIOUS GRAVITATIONAL FIELDS

2021 ◽  
Author(s):  
HAO ZHANG ◽  
HAI-YING LIU ◽  
CHUN-QIU ZHANG ◽  
ZHEN-ZHONG LIU ◽  
WEI WANG
Keyword(s):  
Gravitational Field ◽  
Fluid Shear Stress ◽  
Bone Matrix ◽  
Fluid Pressure ◽  
Gravity Gradient ◽  
Static Compression ◽  
Gravitational Fields ◽  
Multi Scale ◽  
Earth’S Gravitational Field ◽  
Mechanical Microenvironment

Background: Compact bone mainly consists of cylindrical osteon structures. In microgravity, the change in the mechanical microenvironment of osteocytes might be the root cause of astronauts’ bone loss during space flights. Methods: A multi-scale three-dimensional (3D) fluid–solid coupling finite element model of osteons with a two-stage pore structure was developed using COMSOL software based on the natural structure of osteocytes. Gradients in gravitational fields of [Formula: see text]1, 0, 1, 2.5, and 3.7[Formula: see text]g were used to investigate the changes in the mechanical microenvironment on osteocyte structure. The difference in arteriole pulsating pressure and static compression stress caused by each gravity gradient was investigated. Results: The mechanical response of osteocytes increased with the value of g, compared with the Earth’s gravitational field. For instance, the fluid pressure of osteocytes and the von Mises stress of bone matrix near lacunae decreased by 31.3% and 99.9%, respectively, in microgravity. Under static loading, only about 16.7% of osteocytes in microgravity and 58.3% of osteocytes in the Earth’s gravitational field could reach the fluid shear stress threshold of biological reactions in cell culture experiments. Compared with the Earth’s gravitational field, the pressure gradient inside osteocytes severely decreased in microgravity. Conclusion: The mechanical microenvironment of osteocytes in microgravity might cause significant changes in the mechanical microenvironment of osteocytes, which may lead to disuse osteoporosis in astronauts.

Mélanges and disrupted rocks at the leading edge of the Humber Arm Allochthon, W. Newfoundland Appalachians: Deformation under high fluid pressure

2019 ◽  
Vol 74 ◽  
pp. 216-236 ◽  
Author(s):  
Ryan A. Lacombe ◽  
John W.F. Waldron ◽  
S. Henry Williams ◽  
Nicholas B. Harris
Keyword(s):  
Fluid Pressure ◽  
Leading Edge ◽  
High Fluid ◽  
High Fluid Pressure

scholarly journals The Distribution and Origin of Carbonate Cements in Deep-Buried Sandstones in the Central Junggar Basin, Northwest China

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-13 ◽  
Author(s):  
Wang Furong ◽  
He Sheng ◽  
Hou Yuguang ◽  
Dong Tian ◽  
He Zhiliang
Keyword(s):  
Fluid Pressure ◽  
Junggar Basin ◽  
Isotopic Analysis ◽  
Northwest China ◽  
Petrographic Analysis ◽  
Burial Depth ◽  
Depth Range ◽  
High Porosity ◽  
Carbonate Cements ◽  
And Migration

Extremely high porosities and permeabilities are commonly discovered in the sandstones of the Xishanyao Formation in the central Junggar Basin with the burial depth greater than 5500 m, from which hydrocarbons are currently being produced. High content of carbonate cements (up to 20%) is also observed in a similar depth range. Our study aimed to improve our understanding on the origin of carbonate cements in the Xishanyao Formation, in order to provide insights into the existence of high porosity sandstones at greater depths. Integrated analyses including petrographic analysis, isotopic analysis, fluid-inclusion, and core analysis were applied to investigate the distribution and origin of carbonate cements and the influence of high fluid pressure on reservoir quality. Textural evidences demonstrate that there are two generations of carbonate cements, precipitated at the temperature of 90°C and 120°C, respectively. The carbonate cements with low δCPDB13 ranging from −19.07 to -8.95‰ dominantly occurred near the overpressure surface and especially accumulated at approximately 100 m below the surface. Our interpretation is that high content of carbonate cements is significantly influenced by early carbonate cements dissolution and migration under overpressure. Dissolution of plagioclase resulted in the development of internal pores and porosities of as much as 10% at 6500 m depth presumably.

scholarly journals Fracturing and Porosity Channeling in Fluid Overpressure Zones in the Shallow Earth’s Crust

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-17
Author(s):  
Daniel Koehn ◽  
Sandra Piazolo ◽  
Till Sachau ◽  
Renaud Toussaint
Keyword(s):  
Effective Stress ◽  
Fluid Pressure ◽  
Mean Stress ◽  
High Porosity ◽  
Principal Stresses ◽  
Pressure Buildup ◽  
Failure Patterns ◽  
Vertical Zone ◽  
High Fluid ◽  
Fluid Overpressures

At the time of energy transition, it is important to be able to predict the effects of fluid overpressures in different geological scenarios as these can lead to the development of hydrofractures and dilating high-porosity zones. In order to develop an understanding of the complexity of the resulting effective stress fields, fracture and failure patterns, and potential fluid drainage, we study the process with a dynamic hydromechanical numerical model. The model simulates the evolution of fluid pressure buildup, fracturing, and the dynamic interaction between solid and fluid. Three different scenarios are explored: fluid pressure buildup in a sedimentary basin, in a vertical zone, and in a horizontal layer that may be partly offset by a fault. Our results show that the geometry of the area where fluid pressure is successively increased has a first-order control on the developing pattern of porosity changes, on fracturing, and on the absolute fluid pressures that sustained without failure. If the fluid overpressure develops in the whole model, the effective differential and mean stress approach zero and the vertical and horizontal effective principal stresses flip in orientation. The resulting fractures develop under high lithostatic fluid overpressure and are aligned semihorizontally, and consequently, a hydraulic breccia forms. If the area of high fluid pressure buildup is confined in a vertical zone, the effective mean stress decreases while the differential stress remains almost constant and failure takes place in extensional and shear modes at a much lower fluid overpressure. A horizontal fluid pressurized layer that is offset shows a complex system of effective stress evolution with the layer fracturing initially at the location of the offset followed by hydraulic breccia development within the layer. All simulations show a phase transition in the porosity where an initially random porosity reduces its symmetry and forms a static porosity wave with an internal dilating zone and the presence of dynamic porosity channels within this zone. Our results show that patterns of fractures, hence fluid release, that form due to high fluid overpressures can only be successfully predicted if the geometry of the geological system is known, including the fluid overpressure source and the position of seals and faults that offset source layers and seals.

scholarly journals Soft-sediment deformation structures in cores from lacustrine slurry deposits of the Late Triassic Yanchang Fm. (central China)

Geologos ◽  
2016 ◽  
Vol 22 (3) ◽  
pp. 201-211 ◽  
Author(s):  
Renchao Yang ◽  
A.J. (Tom) van Loon ◽  
Wei Yin ◽  
Aiping Fan ◽  
Zuozhen Han
Keyword(s):  
Ordos Basin ◽  
Fluid Pressure ◽  
Volcanic Eruptions ◽  
Central China ◽  
Late Triassic ◽  
Soft Sediment ◽  
Deformation Structures ◽  
Sediment Deformation ◽  
Mass Flows ◽  
Soft Sediment Deformation

Abstract The fine-grained autochthonous sedimentation in the deep part of a Late Triassic lake was frequently interrupted by gravity-induced mass flows. Some of these mass flows were so rich in water that they must have represented slurries. This can be deduced from the soft-sediment deformation structures that abound in cores from these lacustrine deposits which constitute the Yanchang Fm., which is present in the Ordos Basin (central China). The flows and the resulting SSDS were probably triggered by earthquakes, volcanic eruptions, shear stress of gravity flows, and/or the sudden release of overburden-induced excess pore-fluid pressure. The tectonically active setting, the depositional slope and the high sedimentation rate facilitated the development of soft-sediment deformations, which consist mainly of load casts and associated structures such as pseudonodules and flame structures. Sediments with such deformations were occasionally eroded by slurries and became embedded in their deposits.

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