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 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.

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 Frictional properties of anorthite (feldspar): implications for the lower boundary of the seismogenic zone

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Koji Masuda
Keyword(s):  
Dominant Role ◽  
Lower Boundary ◽  
Earthquake Magnitude ◽  
Seismogenic Zone ◽  
Effective Pressure ◽  
Velocity Dependence ◽  
Brittle Deformation ◽  
Frictional Properties ◽  
Depth Extent ◽  
Mineral Constituents

Abstract Earthquake magnitude is closely related to the depth extent of the seismogenic zone, and higher magnitude earthquakes occur where the seismogenic zone is thicker. The frictional properties of the dominant mineral constituents of the crust, such as feldspar-group minerals, control the depth extent of the seismogenic zone. Here, the velocity dependence of the steady-state friction of anorthite, the calcic endmember of the feldspar mineral series, was measured at temperatures from 20 to 600 °C, pore pressures of 0 (“dry”) and 50 MPa (“wet”), and an effective pressure of 150 MPa. The results support previous findings that the frictional properties of feldspar play a dominant role in limiting the depth extent of the seismogenic zone. This evidence suggests that brittle deformation of anorthite may be responsible for brittle fault movements in the brittle–plastic transition zone.

scholarly journals Enhanced lattice distortion, yield strength, critical resolved shear stress, and improving mechanical properties of transition-metals doped CrCoNi medium entropy alloy

RSC Advances ◽  
2021 ◽  
Vol 11 (38) ◽  
pp. 23719-23724
Author(s):  
Md. Lokman Ali
Keyword(s):  
Mechanical Properties ◽  
Shear Stress ◽  
Transition Metals ◽  
Yield Strength ◽  
Lattice Distortion ◽  
Critical Resolved Shear Stress

The effect of transition-metals (TM) addition on the mechanical properties of CrCoNi medium entropy alloys (MEAs) was investigated.

The use of geophysical prospecting for imaging active faults in the Roer Graben, Belgium

Geophysics ◽  
2001 ◽  
Vol 66 (1) ◽  
pp. 78-89 ◽  
Author(s):  
Donat Demanet ◽  
François Renardy ◽  
Kris Vanneste ◽  
Denis Jongmans ◽  
Thierry Camelbeeck ◽  
...  
Keyword(s):  
High Resolution ◽  
Physical Properties ◽  
Fault Zone ◽  
Geophysical Methods ◽  
Depth Range ◽  
Electrical Tomography ◽  
Reflection Seismic ◽  
Refraction Seismic ◽  
Geophysical Surveys ◽  
Geophysical Techniques

As part of a paleoseismological investigation along the Bree fault scarp (western border of the Roer Graben), various geophysical methods [electrical profiling, electromagnetic (EM) profiling, refraction seismic tests, electrical tomography, ground‐penetrating radar (GPR), and high‐resolution reflection seismic profiles] were used to locate and image an active fault zone in a depth range between a few decimeters to a few tens of meters. These geophysical investigations, in parallel with geomorphological and geological analyses, helped in the decision to locate trench excavations exposing the fault surfaces. The results could then be checked with the observations in four trenches excavated across the scarp. Geophysical methods pointed out anomalies at all sites of the fault position. The contrast of physical properties (electrical resistivity and permittivity, seismic velocity) observed between the two fault blocks is a result of a differences in the lithology of the juxtaposed soil layers and of a change in the water table depth across the fault. Extremely fast techniques like electrical and EM profiling or seismic refraction profiles localized the fault position within an accuracy of a few meters. In a second step, more detailed methods (electrical tomography and GPR) more precisely imaged the fault zone and revealed some structures that were observed in the trenches. Finally, one high‐resolution reflection seismic profile imaged the displacement of the fault at depths as large as 120 m and filled the gap between classical seismic reflection profiles and the shallow geophysical techniques. Like all geophysical surveys, the quality of the data is strongly dependent on the geologic environment and on the contrast of the physical properties between the juxtaposed formations. The combined use of various geophysical techniques is thus recommended for fault mapping, particularly for a preliminary investigation when the geological context is poorly defined.

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>

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 Estimating perturbed stress from 3-D borehole displacements induced by fluid injection in fractured or faulted shales

2020 ◽  
Vol 221 (3) ◽  
pp. 1684-1695 ◽  
Author(s):  
Yves Guglielmi ◽  
Christophe Nussbaum ◽  
Jonny Rutqvist ◽  
Frédéric Cappa ◽  
Pierre Jeanne ◽  
...  
Keyword(s):  
Principal Stress ◽  
Fluid Pressure ◽  
Injection Pressure ◽  
Local Stress ◽  
Opalinus Clay ◽  
Step Rate ◽  
Pressure Step ◽  
Heterogeneous Rock ◽  
Magnitude Variation ◽  
Mont Terri

SUMMARY Hydrofracturing stress measurements in fractured and anisotropic shales are notoriously difficult, because opening of existing geological features tends to prevent the creation of a pure hydraulic fracture perpendicular to the least compressive principal stress. Here we show how adding 3-D borehole-displacement measurements while conducting the hydraulic injection test helps to better constrain the principal stress orientations and magnitudes. We developed a 3-D fully coupled hydromechanical numerical model to analyse the displacement, fluid pressure and injection flow-rate data measured during an injection pressure-step-rate test conducted to activate a faulted borehole interval in the Mont Terri Opalinus Clay (Switzerland). We find that injected fluids can only penetrate the fault when it is at or above the Coulomb failure pressure. Borehole displacement orientations are sensitive to a ∼15° variation in the stress–tensor orientation and a 1 MPa stress magnitude variation. Although some dispersion occurs while rupture is propagating along the fault plane ∼4 m away from the borehole, the maximum density of displacement orientations consistently informs about the stress orientation. Thus, an extended injection step-rate approach coupled with an accurate in situ measurement of the borehole wall displacements can be used to better constrain the local stress field perturbations in fractured shales and in heterogeneous rock in general.

Seismotectonics of the Ionian-Akarnania Block (IAB) and Western Greece deduced from a local seismic deployment.

2020 ◽  
Author(s):  
Antoine Haddad ◽  
Athanassios Ganas ◽  
Ioannis Kassaras ◽  
Matteo Lupi
Keyword(s):  
Fault Zone ◽  
Velocity Model ◽  
Focal Mechanisms ◽  
Seismogenic Zone ◽  
The South ◽  
S Wave ◽  
North West ◽  
The North ◽  
Short Period ◽  
Western Greece

<p>From July 2016 to May 2017, we deployed a local seismic network composed of 15 short-period seismic stations to investigate the ongoing seismotectonic deformation of Western Greece with emphasis on the region between Ambrakikos Gulf (to the north) and Kyparissia (to the south). The network was deployed to investigate the behavior of key crustal blocks in western Greece, such as the Ionian-Akarnania Block (IAB).</p><p>After applying automatic P- and S- wave phase picking we located 1200 local earthquakes using HypoInverse and constrained five 1D velocity model by applying the error minimization technique. Events were relocated using HypoDD and 76  focal mechanisms were computed for events with magnitudes down to M<sub>L</sub> 2.3 using first motion polarities.</p><p>We combined the calculated focal mechanisms and the relocated seismicity to shed light on the IAB block boundaries. Three boundaries highlighted by previous studies were also evidenced :</p><p>-The north-west margin of the block, the Cephalonia Transform Fault, Europe‘s most active fault. NW-striking dextral strike-slip motion was recognized for this fault near the Gulf of Myrtos and the town of Fiskardo.</p><p>- The south-east margin is the Movri-Amaliada right-lateral Fault Zone, activated during the Movri Mt. M<sub>w</sub> 6.4 earthquake sequence.</p><p>- The Ambrakikos Gulf (a young E-W rift) and the NW-striking left-lateral Katouna-Stamna Fault zone depict the north and north-eastern margins of the IAB block.</p><p>Seismicity lineaments and focal mechanisms define theKyllini-Cephalonia left-lateral fault, which is also highlighted by bathymetry data. We interpret this fault as the south-western margin of IAB separating an aseismic area observed between Cephalonia and Akarnania from a seismogenic zone north of Zakynthos Island and bridging NW Peloponnese with Cephalonia.</p>

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