Faulting

@article{carlson1957permeability,
    author = "Carlson, Roy W.",
    title = "Permeability, Pore Pressure, and Uplift in Gravity Dams",
    year = "1957",
    journal = "Transactions of the American Society of Civil Engineers",
    url = "https://doi.org/10.1061/taceat.0007421",
    doi = "10.1061/taceat.0007421",
    number = "1",
    openalex = "W2211057396",
    pages = "587-602",
    volume = "122"
}

Promise of resolving the paradox of overthrust faulting arises from a consideration of the influence of the pressure of interstitial fluids upon the effective stresses in rocks. If, in a porous rock filled with a fluid at pressure p, the normal and shear components of total stress across any given plane are S and T, then are the corresponding components of the effective stress in the solid alone. According to the Mohr-Coulomb law, slippage along any internal plane in the rock should occur when the shear stress along that plane reaches the critical value where σ is the normal stress across the plane of slippage, τ 0 the shear strength of the material when σ is zero, and ϕ the angle of internal friction. However, once a fracture is started τ 0 is eliminated, and further slippage results when This can be further simplified by expressing p in terms of S by means of the equation which, when introduced into equation (4), gives From equations (4) and (6) it follows that, without changing the coefficient of friction tan ϕ, the critical value of the shearing stress can be made arbitrarily small simply by increasing the fluid pressure p. In a horizontal block the total weight per unit area S zz is jointly supported by the fluid pressure p and the residual solid stress σ zz; as p is increased, σ zz is correspondingly diminished until, as p approaches the limit S zz, or λ approaches 1, σ zz approaches 0. For the case of gravitational sliding, on a subaerial slope of angle θ where T is the total shear stress, and S the total normal stress on the inclined plane. However, from equations (2) and (6) Then, equating the right-hand terms of equations (7) and (8), we obtain which indicates that the angle of slope θ down which the block will slide can be made to approach 0 as λ approaches 1, corresponding to the approach of the fluid pressure p to the total normal stress S. Hence, given sufficiently high fluid pressures, very much longer fault blocks could be pushed over a nearly horizontal surface, or blocks under their own weight could slide down very much gentler slopes than otherwise would be possible. That the requisite pressures actually do exist is attested by the increasing frequency with which pressures as great as 0.9 S zz are being observed in deep oil wells in various parts of the world.

@article{doi10113000167606195970115rofpim20co2,
    author = "Hubbert, M. King and Rubey, W. W.",
    title = "ROLE OF FLUID PRESSURE IN MECHANICS OF OVERTHRUST FAULTING",
    year = "1959",
    journal = "Geological Society of America Bulletin",
    abstract = "Promise of resolving the paradox of overthrust faulting arises from a consideration of the influence of the pressure of interstitial fluids upon the effective stresses in rocks. If, in a porous rock filled with a fluid at pressure p, the normal and shear components of total stress across any given plane are S and T, then are the corresponding components of the effective stress in the solid alone. According to the Mohr-Coulomb law, slippage along any internal plane in the rock should occur when the shear stress along that plane reaches the critical value where σ is the normal stress across the plane of slippage, τ 0 the shear strength of the material when σ is zero, and ϕ the angle of internal friction. However, once a fracture is started τ 0 is eliminated, and further slippage results when This can be further simplified by expressing p in terms of S by means of the equation which, when introduced into equation (4), gives From equations (4) and (6) it follows that, without changing the coefficient of friction tan ϕ, the critical value of the shearing stress can be made arbitrarily small simply by increasing the fluid pressure p. In a horizontal block the total weight per unit area S zz is jointly supported by the fluid pressure p and the residual solid stress σ zz; as p is increased, σ zz is correspondingly diminished until, as p approaches the limit S zz, or λ approaches 1, σ zz approaches 0. For the case of gravitational sliding, on a subaerial slope of angle θ where T is the total shear stress, and S the total normal stress on the inclined plane. However, from equations (2) and (6) Then, equating the right-hand terms of equations (7) and (8), we obtain which indicates that the angle of slope θ down which the block will slide can be made to approach 0 as λ approaches 1, corresponding to the approach of the fluid pressure p to the total normal stress S. Hence, given sufficiently high fluid pressures, very much longer fault blocks could be pushed over a nearly horizontal surface, or blocks under their own weight could slide down very much gentler slopes than otherwise would be possible. That the requisite pressures actually do exist is attested by the increasing frequency with which pressures as great as 0.9 S zz are being observed in deep oil wells in various parts of the world.",
    url = "https://doi.org/10.1130/0016-7606(1959)70[115:rofpim]2.0.co;2",
    doi = "10.1130/0016-7606(1959)70[115:rofpim]2.0.co;2",
    openalex = "W2724477917"
}

@article{doi10113000167606195970167rofpim20co2,
    author = "Rubey, W. W. and Hubbert, M. King",
    title = "ROLE OF FLUID PRESSURE IN MECHANICS OF OVERTHRUST FAULTING",
    year = "1959",
    journal = "Geological Society of America Bulletin",
    url = "https://doi.org/10.1130/0016-7606(1959)70[167:rofpim]2.0.co;2",
    doi = "10.1130/0016-7606(1959)70[167:rofpim]2.0.co;2",
    openalex = "W2588373281"
}

@article{doi10113000167606196576469rofpim20co2,
    author = "RUBEY, WILLIAM W. and HUBBERT, M. KING",
    title = "ROLE OF FLUID PRESSURE IN MECHANICS OF OVERTHRUST FAULTING: REPLY",
    year = "1965",
    journal = "Geological Society of America Bulletin",
    url = "https://doi.org/10.1130/0016-7606(1965)76[469:rofpim]2.0.co;2",
    doi = "10.1130/0016-7606(1965)76[469:rofpim]2.0.co;2",
    openalex = "W2062507664"
}

@article{crossref1978pore,
    title = "Pore pressure development under offshore gravity structures",
    year = "1978",
    journal = "International Journal of Rock Mechanics and Mining Sciences \& Geomechanics Abstracts",
    url = "https://doi.org/10.1016/0148-9062(78)90153-5",
    doi = "10.1016/0148-9062(78)90153-5",
    number = "3",
    openalex = "W4231883504",
    pages = "61-62",
    volume = "15"
}

Expansion of pore fluid caused by frictional heating might have an important effect on the factional resistance and temperature during an earthquake and a controlling influence on the physics of the earthquake process. When confined water is heated, the pressure increases rapidly (≳10 bars/°C). As Sibson (1973) has pointed out, this could cause a sharp reduction of effective normal stress and dynamic friction on the fault surface. Whether or not this transient stress reduction occurs depends upon the tandem operation of several processes, any of which can break the chain that links frictional heat to frictional stress: the friction must cause an appreciable temperature rise (imposing conditions on the width of the shear zone and rate of conductive transport); the temperature rise must cause an appreciable fluid pressure rise (imposing conditions on the rate of pore dilatation or hydrofracturing, and the rate of Darcian transport); the fluid pressure rise must cause an appreciable reduction of friction (requiring the presence of a continuous fluid phase). Each process depends upon event duration, particle velocity, and the initial value of dynamic friction. With the present uncertainty in the controlling parameters (principally permeability, width of the shear zone, initial stress, and factors controlling transient hydrofracture and pore dilatation) a wide variety of fault behavior is possible. Limits to fault behavior for various ranges of the controlling parameters can be estimated from the governing equations, however, and results can be summarized graphically. If the effective stress law applies and pore dilatation is unimportant, dynamic friction would drop from an initial value of 1 kbar to ∼100 bars when shear strain reached 10 for most earthquakes if the permeability were less than 0.1 μdarcy; the maximum temperature rise would be only ∼150°C irrespective of final strain. If the permeability were ≳100 mdarcies, however, friction would be unaffected by faulting and temperatures could approach melting for shear strains ∼20. For permeabilities ∼1 mdarcy, friction could be reduced appreciably during large earthquakes, but during small ones it could not. Combined with thermal effects, dilatational strain of a few percent of pore volume could lead to virtually frictionless faulting or increasing frictional resistance, dependeing upon its sign; unstable propagation of hydrofractures (after fluid pressure exceeded the least principal stress) could cause a sudden increase in fault friction. Strengthening due to cooling and Darcian flow at the conclusion of an earthquake could occur in seconds or weeks depending upon event duration, transport parameters, and shear zone width; it might influence the redistribution of stress by aftershocks.

@article{doi101029jb085ib11p06097,
    author = "Lachenbruch, Arthur H.",
    title = "Frictional heating, fluid pressure, and the resistance to fault motion",
    year = "1980",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Expansion of pore fluid caused by frictional heating might have an important effect on the factional resistance and temperature during an earthquake and a controlling influence on the physics of the earthquake process. When confined water is heated, the pressure increases rapidly (≳10 bars/°C). As Sibson (1973) has pointed out, this could cause a sharp reduction of effective normal stress and dynamic friction on the fault surface. Whether or not this transient stress reduction occurs depends upon the tandem operation of several processes, any of which can break the chain that links frictional heat to frictional stress: the friction must cause an appreciable temperature rise (imposing conditions on the width of the shear zone and rate of conductive transport); the temperature rise must cause an appreciable fluid pressure rise (imposing conditions on the rate of pore dilatation or hydrofracturing, and the rate of Darcian transport); the fluid pressure rise must cause an appreciable reduction of friction (requiring the presence of a continuous fluid phase). Each process depends upon event duration, particle velocity, and the initial value of dynamic friction. With the present uncertainty in the controlling parameters (principally permeability, width of the shear zone, initial stress, and factors controlling transient hydrofracture and pore dilatation) a wide variety of fault behavior is possible. Limits to fault behavior for various ranges of the controlling parameters can be estimated from the governing equations, however, and results can be summarized graphically. If the effective stress law applies and pore dilatation is unimportant, dynamic friction would drop from an initial value of 1 kbar to ∼100 bars when shear strain reached 10 for most earthquakes if the permeability were less than 0.1 μdarcy; the maximum temperature rise would be only ∼150°C irrespective of final strain. If the permeability were ≳100 mdarcies, however, friction would be unaffected by faulting and temperatures could approach melting for shear strains ∼20. For permeabilities ∼1 mdarcy, friction could be reduced appreciably during large earthquakes, but during small ones it could not. Combined with thermal effects, dilatational strain of a few percent of pore volume could lead to virtually frictionless faulting or increasing frictional resistance, dependeing upon its sign; unstable propagation of hydrofractures (after fluid pressure exceeded the least principal stress) could cause a sudden increase in fault friction. Strengthening due to cooling and Darcian flow at the conclusion of an earthquake could occur in seconds or weeks depending upon event duration, transport parameters, and shear zone width; it might influence the redistribution of stress by aftershocks.",
    url = "https://doi.org/10.1029/jb085ib11p06097",
    doi = "10.1029/jb085ib11p06097",
    openalex = "W2039285506"
}

@article{guth1982limitations,
    author = "GUTH, PETER L. and HODGES, KIP V. and WILLEMIN, JAMES H.",
    title = "Limitations on the role of pore pressure in gravity gliding",
    year = "1982",
    journal = "Geological Society of America Bulletin",
    url = "https://doi.org/10.1130/0016-7606(1982)93<606:lotrop>2.0.co;2",
    doi = "10.1130/0016-7606(1982)93<606:lotrop>2.0.co;2",
    number = "7",
    openalex = "W2110946136",
    pages = "606",
    volume = "93"
}

@techreport{guth1982limitations1,
    author = "Guth, P. L. and Hodges, L. V. and Willemin, J. H",
    title = "Limitations on the role of pore pressure in gravity sliding",
    year = "1982",
    howpublished = "Geological Society of America Bulletin, v. 93, p. 611",
    note = "talkorigins\_source = {true}; raw\_reference = {Guth, P. L., Hodges, L. V., and Willemin, J. H., 1982, Limitations on the role of pore pressure in gravity sliding: Geological Society of America Bulletin, v. 93, p. 611.}"
}

@article{crossref1983limitations,
    title = "Limitations on the role of pore pressure in gravity gliding",
    year = "1983",
    journal = "International Journal of Rock Mechanics and Mining Sciences \& Geomechanics Abstracts",
    url = "https://doi.org/10.1016/0148-9062(83)90387-x",
    doi = "10.1016/0148-9062(83)90387-x",
    number = "2",
    openalex = "W4237918989",
    pages = "A39",
    volume = "20"
}

@article{doi10113000917613198311279ldamve20co2,
    author = "Westbrook, Graham K. and Smith, M. J.",
    title = "Long decollements and mud volcanoes: Evidence from the Barbados Ridge Complex for the role of high pore-fluid pressure in the development of an accretionary complex",
    year = "1983",
    journal = "Geology",
    url = "https://doi.org/10.1130/0091-7613(1983)11<279:ldamve>2.0.co;2",
    doi = "10.1130/0091-7613(1983)11<279:ldamve>2.0.co;2",
    openalex = "W1987216519"
}

@incollection{crossref1984thinskinned,
    title = "Thin-Skinned Gravity Sliding as a Mechanism for Growth Faulting",
    year = "1984",
    booktitle = "Structural and Depositional Styles of Gulf Coast Tertiary Continental Margins",
    url = "https://doi.org/10.1306/ce25434c10",
    doi = "10.1306/ce25434c10",
    openalex = "W4243627427",
    pages = "37-45"
}

Many mesothermal gold-quartz deposits are localized along high-angle reverse or reverse-oblique shear zones within greenstone belt terrains. Characteristically, these fault-hosted vein deposits exhibit a mixed brittle-ductile style of deformation (discrete shears and vein fractures as well as a schistose shear-zone fabric) developed under greenschist facies metamorphic conditions. Many of the vein systems are of considerable vertical extent (>2 km); they include steeply dipping fault veins (lenticular veins subparallel to the shear-zone schistosity) and, in some cases, associated flats (subhorizontal extensional veins). Textures of both vein sets record histories of incremental deposition. We infer that the vein sets developed near the roofs of active metamorphic/magmatic systems and represent the roots of brittle, high-angle reverse fault systems extending upward through the seismogenic regime. Friction theory and field relations suggest that the high-angle reverse faults acted as valves, promoting cyclic fluctuations in fluid pressure from supralithostatic to hydrostatic values. Because of their unfavorable orientation in the prevailing stress field, reactivation of the faults could only occur when fluid pressure exceeded the lithostatic load. Seismogenic fault failure then created fracture permeability within the rupture zone, allowing sudden draining of the geopressured reservoir at depth. Incremental opening of flats is attributed to the prefailure stage of supralithostatic fluid pressures; deposition within fault veins is attributed to the immediate postfailure discharge phase. Hydrothermal self-sealing leads to reaccumulation of fluid pressure and a repetition of the cycle. Mutual crosscutting relations between the two vein sets are a natural consequence of the cyclicity of the process. Abrupt fluid-pressure fluctuations from this fault-valve behavior of reverse faults seem likely to be integral to the mineralizing process at this structural level.

@article{doi1011300091761319880160551harffp23co2,
    author = "Sibson, Richard H. and Robert, F. and Poulsen, K H",
    title = "High-angle reverse faults, fluid-pressure cycling, and mesothermal gold-quartz deposits",
    year = "1988",
    journal = "Geology",
    abstract = "Many mesothermal gold-quartz deposits are localized along high-angle reverse or reverse-oblique shear zones within greenstone belt terrains. Characteristically, these fault-hosted vein deposits exhibit a mixed brittle-ductile style of deformation (discrete shears and vein fractures as well as a schistose shear-zone fabric) developed under greenschist facies metamorphic conditions. Many of the vein systems are of considerable vertical extent (>2 km); they include steeply dipping fault veins (lenticular veins subparallel to the shear-zone schistosity) and, in some cases, associated flats (subhorizontal extensional veins). Textures of both vein sets record histories of incremental deposition. We infer that the vein sets developed near the roofs of active metamorphic/magmatic systems and represent the roots of brittle, high-angle reverse fault systems extending upward through the seismogenic regime. Friction theory and field relations suggest that the high-angle reverse faults acted as valves, promoting cyclic fluctuations in fluid pressure from supralithostatic to hydrostatic values. Because of their unfavorable orientation in the prevailing stress field, reactivation of the faults could only occur when fluid pressure exceeded the lithostatic load. Seismogenic fault failure then created fracture permeability within the rupture zone, allowing sudden draining of the geopressured reservoir at depth. Incremental opening of flats is attributed to the prefailure stage of supralithostatic fluid pressures; deposition within fault veins is attributed to the immediate postfailure discharge phase. Hydrothermal self-sealing leads to reaccumulation of fluid pressure and a repetition of the cycle. Mutual crosscutting relations between the two vein sets are a natural consequence of the cyclicity of the process. Abrupt fluid-pressure fluctuations from this fault-valve behavior of reverse faults seem likely to be integral to the mineralizing process at this structural level.",
    url = "https://doi.org/10.1130/0091-7613(1988)016<0551:harffp>2.3.co;2",
    doi = "10.1130/0091-7613(1988)016<0551:harffp>2.3.co;2",
    openalex = "W2004131413"
}

Low‐angle (dip < 30°) normal faults accommodate much extension of the continental crust. They apparently move under low resolved shear stress and are anomalously weak, characteristics that they share with the San Andreas fault. Structural, textural, and geochemical arguments suggest that low‐angle normal faults are weak in both the ductile and brittle regimes, partly or totally due to elevated pore fluid pressure. High pore pressure in detachment zones may be contained by upper‐plate strata, mineral precipitation in their hanging walls, formation of low‐permeability microbreccia layers, threshold pressure gradients, and low‐permeability mylonites below chlorite breccia. Mechanical analysis shows that fault weakening may preclude equality of the regional and fault‐zone stress tensors, and predicts reorientation and increase of principal stresses in weak fault zones. These changes suppress hydraulic fracturing in the brittle detachment zone and allow slip under frictional sliding conditions typical of upper crustal rocks. Fault weakening focuses extension in the upper crust onto low‐angle normal ductile‐brittle shear zones in the midcrust, promoting propagation of low‐angle brittle normal faults into the upper crust.

@article{doi10102992jb00517,
    author = "Axen, Gary J.",
    title = "Pore pressure, stress increase, and fault weakening in low‐angle normal faulting",
    year = "1992",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "Low‐angle (dip < 30°) normal faults accommodate much extension of the continental crust. They apparently move under low resolved shear stress and are anomalously weak, characteristics that they share with the San Andreas fault. Structural, textural, and geochemical arguments suggest that low‐angle normal faults are weak in both the ductile and brittle regimes, partly or totally due to elevated pore fluid pressure. High pore pressure in detachment zones may be contained by upper‐plate strata, mineral precipitation in their hanging walls, formation of low‐permeability microbreccia layers, threshold pressure gradients, and low‐permeability mylonites below chlorite breccia. Mechanical analysis shows that fault weakening may preclude equality of the regional and fault‐zone stress tensors, and predicts reorientation and increase of principal stresses in weak fault zones. These changes suppress hydraulic fracturing in the brittle detachment zone and allow slip under frictional sliding conditions typical of upper crustal rocks. Fault weakening focuses extension in the upper crust onto low‐angle normal ductile‐brittle shear zones in the midcrust, promoting propagation of low‐angle brittle normal faults into the upper crust.",
    url = "https://doi.org/10.1029/92jb00517",
    doi = "10.1029/92jb00517",
    openalex = "W2135668552",
    references = "doi101007bf00876528, doi1010160191814189900369, doi101029jb073i006p02225, doi101029jb085ib11p06248, doi101029jb088ib05p04183, doi101038291645a0, doi101126science23848301105, doi10113000167606195970115rofpim20co2, doi101130001676061970813513ioptft20co2, doi10113000167606198293606lotrop20co2, doi1011300091761319880160551harffp23co2, guth1982limitations"
}

@article{openalexw3096527154,
    author = "Rice, J. R.",
    title = "Fault stress states, pore pressure distributions, and the weakness of the San Andreas Fault",
    year = "1992",
    journal = "Medical Entomology and Zoology",
    openalex = "W3096527154"
}

We analyze the conditions for unstable slip of a fluid infiltrated fault using a rate and state dependent friction model including the effects of dilatancy and pore compaction. We postulate the existence of a steady state drained porosity of the fault gouge which depends on slip velocity as ϕ ss = ϕ 0 + εln(v / v 0) over the range considered, where v is sliding velocity and ε and v 0 are constants. Porosity evolves toward steady state over the same distance scale, d c, as “state.” This constitutive model predicts changes in porosity upon step changes in sliding velocity that are consistent with the drained experiments of Marone et al. (1990). For undrained loading, the effect of dilatancy is to increase (strengthen) ∂τ ss /∂ln v by μ ss ε/(σ – p)β where μ ss is steady state friction, σ and p are fault normal stress and pore pressure, and β is a combination of fluid and pore compressibilities. Assuming ε ∼ 1.7×10 −4 from fitting the Marone et al. data, we find the “dilatancy strengthening” effect to be reasonably consistent with undrained tests conducted by Lockner and Byerlee (1994). Linearized perturbation analysis of a single degree of freedom model in steady sliding shows that unstable slip occurs if the spring stiffness is less than a critical value given by k crit = (σ‐ p)(b ‐ a)/ d c ‐ εμ ss F (c *)/β d c where a and b are coefficients in the friction law and F (C *) is a function of the model hydraulic diffusivity c * (diffusivity/diffusion length 2). In the limit c * →∞ F (c *) → 0, recovering the drained result of Ruina (1983). In the undrained limit, c * → 0, F (c *) → 1, so that for sufficiently large ε slip is always stable to small perturbations. Under undrained conditions (σ – p) must exceed εμ ss /β(b ‐ a) for instabilities to nucleate, even for arbitrarily reduced stiffness. This places constraints on how high the fault zone pore pressure can be, to rationalize the absence of a heat flow anomaly on the San Andreas fault, and still allow earthquakes to nucleate without concommitant fluid transport. For the dilatancy constitutive laws examined here, numerical simulations do not exhibit large interseismic increases in fault zone pore pressure. The simulations do, however, exhibit a wide range of interesting behavior including: sustained finite amplitude oscillations near steady state and repeating stick slip events in which the stress drop decreases with decreasing diffusivity, a result of dilatancy strengthening. For some parameter values we observe “aftershock” like events that follow the principal stick‐slip event. These aftershocks are noteworthy in that they involve rerupture of the surface due to the interaction of the dilatancy and slip weakening effects rather than to interaction with neighboring portions of the fault. This mechanism may explain aftershocks that appear to be located within zones of high mainshock slip, although poor resolution in mainshock slip distributions can not be ruled out.

@article{doi10102995jb02403,
    author = "Segall, P. and Rice, J. R.",
    title = "Dilatancy, compaction, and slip instability of a fluid‐infiltrated fault",
    year = "1995",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "We analyze the conditions for unstable slip of a fluid infiltrated fault using a rate and state dependent friction model including the effects of dilatancy and pore compaction. We postulate the existence of a steady state drained porosity of the fault gouge which depends on slip velocity as ϕ ss = ϕ 0 + εln(v / v 0) over the range considered, where v is sliding velocity and ε and v 0 are constants. Porosity evolves toward steady state over the same distance scale, d c, as “state.” This constitutive model predicts changes in porosity upon step changes in sliding velocity that are consistent with the drained experiments of Marone et al. (1990). For undrained loading, the effect of dilatancy is to increase (strengthen) ∂τ ss /∂ln v by μ ss ε/(σ – p)β where μ ss is steady state friction, σ and p are fault normal stress and pore pressure, and β is a combination of fluid and pore compressibilities. Assuming ε ∼ 1.7×10 −4 from fitting the Marone et al. data, we find the “dilatancy strengthening” effect to be reasonably consistent with undrained tests conducted by Lockner and Byerlee (1994). Linearized perturbation analysis of a single degree of freedom model in steady sliding shows that unstable slip occurs if the spring stiffness is less than a critical value given by k crit = (σ‐ p)(b ‐ a)/ d c ‐ εμ ss F (c *)/β d c where a and b are coefficients in the friction law and F (C *) is a function of the model hydraulic diffusivity c * (diffusivity/diffusion length 2). In the limit c * →∞ F (c *) → 0, recovering the drained result of Ruina (1983). In the undrained limit, c * → 0, F (c *) → 1, so that for sufficiently large ε slip is always stable to small perturbations. Under undrained conditions (σ – p) must exceed εμ ss /β(b ‐ a) for instabilities to nucleate, even for arbitrarily reduced stiffness. This places constraints on how high the fault zone pore pressure can be, to rationalize the absence of a heat flow anomaly on the San Andreas fault, and still allow earthquakes to nucleate without concommitant fluid transport. For the dilatancy constitutive laws examined here, numerical simulations do not exhibit large interseismic increases in fault zone pore pressure. The simulations do, however, exhibit a wide range of interesting behavior including: sustained finite amplitude oscillations near steady state and repeating stick slip events in which the stress drop decreases with decreasing diffusivity, a result of dilatancy strengthening. For some parameter values we observe “aftershock” like events that follow the principal stick‐slip event. These aftershocks are noteworthy in that they involve rerupture of the surface due to the interaction of the dilatancy and slip weakening effects rather than to interaction with neighboring portions of the fault. This mechanism may explain aftershocks that appear to be located within zones of high mainshock slip, although poor resolution in mainshock slip distributions can not be ruled out.",
    url = "https://doi.org/10.1029/95jb02403",
    doi = "10.1029/95jb02403",
    openalex = "W2083658020"
}

The slip behavior of major faults depends largely on the frictional and hydrologic properties of fault gouge. We report on laboratory experiments designed to measure the strength, friction constitutive properties, and permeability of a suite of saturated clay‐rich fault gouges, including: a 50:50% mixture of montmorillonite‐quartz, powdered illite shale, and powdered chlorite schist. Friction measurements indicate that clay‐rich gouges are consistently weak, with steady state coefficient of sliding friction of <0.35. The montmorillonite gouge (μ = 0.19–0.23) is consistently weaker than the illite and chlorite gouges (μ = 0.27–0.32). At effective normal stresses from 12 to 59 MPa, all gouges show velocity‐strengthening frictional behavior in the sliding velocity range 0.5–300 μ m/s. We suggest that the velocity‐strengthening behavior we observe is related to saturation of real contact area, as documented by the friction parameter b, and is an inherent characteristic of noncohesive, unlithified clay‐rich gouge. Permeability normal to the gouge layer measured before, during, and after shear ranges from 8.3 × 10 −21 m 2 to 3.6 × 10 −16 m 2; permeability decreases dramatically with shearing, and to a lesser extent with increasing effective normal stress. The chlorite gouge is consistently more permeable than the montmorillonite and illite gouge and maintains a higher permeability after shearing. Permeability reduction via shear is pronounced at shear strains ≲5 and is smaller at higher strain, suggesting that shear‐induced permeability reduction is linked to fabric development early in the deformation history. Our results imply that the potential for development of excess pore pressure in low‐permeability fault gouge depends on both clay mineralogy and shear strain.

@article{doi1010292008jb006089,
    author = "Ikari, Matt J. and Saffer, D. M. and Marone, Chris",
    title = "Frictional and hydrologic properties of clay‐rich fault gouge",
    year = "2009",
    journal = "Journal of Geophysical Research Atmospheres",
    abstract = "The slip behavior of major faults depends largely on the frictional and hydrologic properties of fault gouge. We report on laboratory experiments designed to measure the strength, friction constitutive properties, and permeability of a suite of saturated clay‐rich fault gouges, including: a 50:50\% mixture of montmorillonite‐quartz, powdered illite shale, and powdered chlorite schist. Friction measurements indicate that clay‐rich gouges are consistently weak, with steady state coefficient of sliding friction of <0.35. The montmorillonite gouge (μ = 0.19–0.23) is consistently weaker than the illite and chlorite gouges (μ = 0.27–0.32). At effective normal stresses from 12 to 59 MPa, all gouges show velocity‐strengthening frictional behavior in the sliding velocity range 0.5–300 μ m/s. We suggest that the velocity‐strengthening behavior we observe is related to saturation of real contact area, as documented by the friction parameter b, and is an inherent characteristic of noncohesive, unlithified clay‐rich gouge. Permeability normal to the gouge layer measured before, during, and after shear ranges from 8.3 × 10 −21 m 2 to 3.6 × 10 −16 m 2; permeability decreases dramatically with shearing, and to a lesser extent with increasing effective normal stress. The chlorite gouge is consistently more permeable than the montmorillonite and illite gouge and maintains a higher permeability after shearing. Permeability reduction via shear is pronounced at shear strains ≲5 and is smaller at higher strain, suggesting that shear‐induced permeability reduction is linked to fabric development early in the deformation history. Our results imply that the potential for development of excess pore pressure in low‐permeability fault gouge depends on both clay mineralogy and shear strain.",
    url = "https://doi.org/10.1029/2008jb006089",
    doi = "10.1029/2008jb006089",
    openalex = "W2026254189",
    references = "doi101016s0012821x03004242, doi1011300091761320010290183ulotsz20co2"
}

Clarey's (2012) model for South Fork (SF) thrusting contains major errors as regards timing of emplacement, number of emplacement events, magnitude of displacement, and geometry of the SF allochthon. A model better supported by data: (1) has SF thrusting taking place before local emplacement of the Heart Mountain (HM) allochthon, rather than after; (2) has emplacement of the SF allochthon by multiple events rather than by a single catastrophic event; (3) envisions only gradual changes in the magnitude of displacement along strike of the SF thrust system, rather than abrupt doubling of displacement across tear faults; (4) regards the SF allochthon as segmented by tear faults only where it has moved across footwall lateral ramps, not in its hinterland; and (5) recognizes that the fault viewed by Clarey (2012) as a break-away to the SF system is instead a fault within the HM allochthon. Clarey's (2012) claim that SF thrusting postdated emplacement of the HM allochthon is based on his assertion that the HM detachment and overlying allochthon are folded above the SF frontal ramp, both on his section A–A′ and near the Castle fault. This argument is disproven by the geologic map of Pierce and Nelson (1969), which presents a much more complete picture of relevant relationships than is shown in Clarey (2012). Pierce and Nelson's (1969) cross section A–A′ is drawn where the preserved HM allochthon and the SF frontal ramp are in …

@article{doi102113gsrocky48163,
    author = "Hauge, Thomas A.",
    title = "South Fork Fault as a gravity slide: Its break-away, timing, and emplacement, northwestern Wyoming, U.S.A.: COMMENT",
    year = "2013",
    journal = "Rocky Mountain geology",
    abstract = "Clarey's (2012) model for South Fork (SF) thrusting contains major errors as regards timing of emplacement, number of emplacement events, magnitude of displacement, and geometry of the SF allochthon. A model better supported by data: (1) has SF thrusting taking place before local emplacement of the Heart Mountain (HM) allochthon, rather than after; (2) has emplacement of the SF allochthon by multiple events rather than by a single catastrophic event; (3) envisions only gradual changes in the magnitude of displacement along strike of the SF thrust system, rather than abrupt doubling of displacement across tear faults; (4) regards the SF allochthon as segmented by tear faults only where it has moved across footwall lateral ramps, not in its hinterland; and (5) recognizes that the fault viewed by Clarey (2012) as a break-away to the SF system is instead a fault within the HM allochthon. Clarey's (2012) claim that SF thrusting postdated emplacement of the HM allochthon is based on his assertion that the HM detachment and overlying allochthon are folded above the SF frontal ramp, both on his section A–A′ and near the Castle fault. This argument is disproven by the geologic map of Pierce and Nelson (1969), which presents a much more complete picture of relevant relationships than is shown in Clarey (2012). Pierce and Nelson's (1969) cross section A–A′ is drawn where the preserved HM allochthon and the SF frontal ramp are in …",
    url = "https://doi.org/10.2113/gsrocky.48.1.63",
    doi = "10.2113/gsrocky.48.1.63",
    openalex = "W2326560907",
    references = "doi102113gsrocky47155"
}

Overthrust faults have been a source of debate and discussion in creation literature for many years. Their interpretation demands a better explanation in a Flood context. Two fault systems are examined as analogies for an “overthrust” model. The South Fork Fault System (SFFS) and the Heart Mountain Fault System (HMFS) exhibit folding and faulting consistent with thin-skinned overthrust systems. Both systems moved catastrophically under the influence of gravity. The South Fork Fault system (SFFS, southwest of Cody, Wyoming, exhibits tear faults, tight folds, a triangle zone, and flat-ramp geometries along the leading edge of the system. Transport was southeast, down a gentle slope during early to middle Eocene time (Late Flood), approximately coeval with the Heart Mountain Fault system (HMFS). The SFFS detaches in lower Jurassic strata, rich in gypsum-anhydrite, overlain by about 1250 m of Jurassic through Tertiary sedimentary and volcanic rocks. Movement between 5 km and 10 km to the southeast spread the allochthonous mass over an area exceeding 1400 km2. A break-away fault and an area of tectonic denudation mark the upper northwest part of the system. The exposed denuded surface was buried by additional Eocene-age volcanic rocks soon after slip. Catastrophic rear-loading during emplacement of HMFS may have initiated subsequent movement on the SFFS, with dehydration processes trapping water in a near frictionless anhydrite-water slurry. Rapid development of near-surface folds, as observed in the toe of the SFFS, could only have developed while the sediments were still unlithified.

@article{openalexw3092008185,
    author = "Clarey, Timothy L.",
    title = "South Fork and Heart Mountain Faults: Examples of Catastrophic, Gravity-Driven “Overthrusts,” Northwest Wyoming, USA",
    year = "2013",
    journal = "DigitalCommons-Cedarville (Cedarville University)",
    abstract = "Overthrust faults have been a source of debate and discussion in creation literature for many years. Their interpretation demands a better explanation in a Flood context. Two fault systems are examined as analogies for an “overthrust” model. The South Fork Fault System (SFFS) and the Heart Mountain Fault System (HMFS) exhibit folding and faulting consistent with thin-skinned overthrust systems. Both systems moved catastrophically under the influence of gravity. The South Fork Fault system (SFFS, southwest of Cody, Wyoming, exhibits tear faults, tight folds, a triangle zone, and flat-ramp geometries along the leading edge of the system. Transport was southeast, down a gentle slope during early to middle Eocene time (Late Flood), approximately coeval with the Heart Mountain Fault system (HMFS). The SFFS detaches in lower Jurassic strata, rich in gypsum-anhydrite, overlain by about 1250 m of Jurassic through Tertiary sedimentary and volcanic rocks. Movement between 5 km and 10 km to the southeast spread the allochthonous mass over an area exceeding 1400 km2. A break-away fault and an area of tectonic denudation mark the upper northwest part of the system. The exposed denuded surface was buried by additional Eocene-age volcanic rocks soon after slip. Catastrophic rear-loading during emplacement of HMFS may have initiated subsequent movement on the SFFS, with dehydration processes trapping water in a near frictionless anhydrite-water slurry. Rapid development of near-surface folds, as observed in the toe of the SFFS, could only have developed while the sediments were still unlithified.",
    openalex = "W3092008185",
    references = "doi101029jb088ib02p01153, doi10113000167606195970115rofpim20co2, doi10113000167606195970167rofpim20co2, doi10113000167606196576469rofpim20co2, doi101130001676061978891189motfb20co2, doi10113000167606198293606lotrop20co2, doi1011300016760619881001898tmpolo23co2, doi101130b26340, doi102113gsrocky47155, doi105860choice460896, guth1982limitations, openalexw2107320391, openalexw2965328582, openalexw641576879"
}

Movement of gravity-driven systems on passive margins is fuelled by the loss of gravitational potential energy. Two end-member modes (gravity spreading and gravity gliding) are defined by whether the potential energy loss is due to deformation and movement towards the base of the system (spreading), or by movement parallel to the base of the system (gliding); most natural systems consist of a mixture of the two processes. Hitherto, use of these concepts has been limited or equivocal due to lack of a quantitative measure. In some cases, characterisation of gliding vs. spreading systems based on secondary attributes has resulted in controversy, because there is a lack of consensus as to which of these are truly diagnostic. This paper presents a new, simple quantitative method based on vector analysis, providing a numerical measure of the relative contribution of spreading vs. gliding. The method is applied to synthetic examples, where deformation can be tracked, and to natural examples where a valid palinspastic reconstruction is available. The results confirm that most natural examples exhibit mixed-mode behaviour, and that some have been mischaracterized; much of the Angola margin is dominated by spreading. The method can also provide an estimate of the absolute amount of gravitational potential energy released in the movement, and the energy contribution made by gliding vs. spreading. Determining the dominant process has implications for predicting the development of seafloor topography and stratal architecture.

@article{doi101016jtecto201406023,
    author = "Peel, Frank",
    title = "The engines of gravity-driven movement on passive margins: Quantifying the relative contribution of spreading vs. gravity sliding mechanisms",
    year = "2014",
    journal = "Tectonophysics",
    abstract = "Movement of gravity-driven systems on passive margins is fuelled by the loss of gravitational potential energy. Two end-member modes (gravity spreading and gravity gliding) are defined by whether the potential energy loss is due to deformation and movement towards the base of the system (spreading), or by movement parallel to the base of the system (gliding); most natural systems consist of a mixture of the two processes. Hitherto, use of these concepts has been limited or equivocal due to lack of a quantitative measure. In some cases, characterisation of gliding vs. spreading systems based on secondary attributes has resulted in controversy, because there is a lack of consensus as to which of these are truly diagnostic. This paper presents a new, simple quantitative method based on vector analysis, providing a numerical measure of the relative contribution of spreading vs. gliding. The method is applied to synthetic examples, where deformation can be tracked, and to natural examples where a valid palinspastic reconstruction is available. The results confirm that most natural examples exhibit mixed-mode behaviour, and that some have been mischaracterized; much of the Angola margin is dominated by spreading. The method can also provide an estimate of the absolute amount of gravitational potential energy released in the movement, and the energy contribution made by gliding vs. spreading. Determining the dominant process has implications for predicting the development of seafloor topography and stratal architecture.",
    url = "https://doi.org/10.1016/j.tecto.2014.06.023",
    doi = "10.1016/j.tecto.2014.06.023",
    openalex = "W2058198578",
    references = "doi101016jearscirev201009010, doi101016jmarpetgeo201103004, doi101144gslsp19870290114"
}

Abstract In a context of global change and increasing anthropic pressure on the environment, monitoring the Earth system and its evolution has become one of the key missions of geosciences. Geodesy is the geoscience that measures the geometric shape of the Earth, its orientation in space, and gravity field. Time‐variable gravity, because of its high accuracy, can be used to build an enhanced picture and understanding of the changing Earth. Ground‐based gravimetry can determine the change in gravity related to the Earth rotation fluctuation, to celestial body and Earth attractions, to the mass in the direct vicinity of the instruments, and to vertical displacement of the instrument itself on the ground. In this paper, we review the geophysical questions that can be addressed by ground gravimeters used to monitor time‐variable gravity. This is done in relation to the instrumental characteristics, noise sources, and good practices. We also discuss the next challenges to be met by ground gravimetry, the place that terrestrial gravimetry should hold in the Earth observation system, and perspectives and recommendations about the future of ground gravity instrumentation.

@article{doi1010022017rg000566,
    author = "Camp, Michel Van and de Viron, O. and Watlet, Arnaud and Meurers, Bruno and Francis, Olivier and Caudron, Corentin",
    title = "Geophysics From Terrestrial Time‐Variable Gravity Measurements",
    year = "2017",
    journal = "Reviews of Geophysics",
    abstract = "Abstract In a context of global change and increasing anthropic pressure on the environment, monitoring the Earth system and its evolution has become one of the key missions of geosciences. Geodesy is the geoscience that measures the geometric shape of the Earth, its orientation in space, and gravity field. Time‐variable gravity, because of its high accuracy, can be used to build an enhanced picture and understanding of the changing Earth. Ground‐based gravimetry can determine the change in gravity related to the Earth rotation fluctuation, to celestial body and Earth attractions, to the mass in the direct vicinity of the instruments, and to vertical displacement of the instrument itself on the ground. In this paper, we review the geophysical questions that can be addressed by ground gravimeters used to monitor time‐variable gravity. This is done in relation to the instrumental characteristics, noise sources, and good practices. We also discuss the next challenges to be met by ground gravimetry, the place that terrestrial gravimetry should hold in the Earth observation system, and perspectives and recommendations about the future of ground gravity instrumentation.",
    url = "https://doi.org/10.1002/2017rg000566",
    doi = "10.1002/2017rg000566",
    openalex = "W2759383864",
    references = "doi1010022015rg000502, doi1010160031920181900467, doi101029rg024i003p00579, doi101071pvv2011n155other, doi101103physrevlett116061102, doi101126science1099192, doi101126science1108339, doi101126science1227079, doi1011371010093, doi101175bams853381, doi101256qj04176, openalexw2315214008"
}

Abstract Normal faults commonly represent one of the principal controls on the origin and formation of sedimentary rock-hosted mineral deposits. Their presence within rift basins has a profound effect on fluid flow, with their impact ranging from acting as barriers, causing pressure compartmentalization of basinal pore fluids, to forming conduits for up-fault fluid flow. Despite their established importance in controlling the migration and trapping of mineralizing fluids, we have yet to adequately reconcile this duality of flow behavior and its impact on mineral flow systems within basinal sequences from a semiquantitative to quantitative perspective. Combining insights and models derived from earthquake, hydrocarbon, and mineral studies, the principal processes and models for fault-related fluid flow within sedimentary basins are reviewed and a unified conceptual model defined for their role in mineral systems. We illustrate associated concepts with case studies from Irish-type Zn-Pb deposits, sedimentary rock-hosted Cu deposits, and active sedimentary basins. We show that faults can actively affect fluid flow by a variety of associated processes, including seismic pumping and pulsing, or can provide pathways for the upward flow of overpressured fluids or the downward sinking of heavy brines. Associated models support the generation of crustal-scale convective flow systems that underpin the formation of major mineral provinces and provide a basis for differences in the flow behavior of faults, depending on a variety of factors such as fault zone complexities, host-rock properties, deformation conditions, and pressure drives. Flow heterogeneity along faults provides a basis for the thoroughly 3D flow systems that localize fluid flow and lead to the formation of mineral deposits.

@incollection{doi105382sp2111,
    author = "Walsh, John J. and Torremans, Koen and Güven, John and Kyne, Roisin and Conneally, John and Bonson, C.G",
    title = "Fault-Controlled Fluid Flow Within Extensional Basins and Its Implications for Sedimentary Rock-Hosted Mineral Deposits",
    year = "2018",
    abstract = "Abstract Normal faults commonly represent one of the principal controls on the origin and formation of sedimentary rock-hosted mineral deposits. Their presence within rift basins has a profound effect on fluid flow, with their impact ranging from acting as barriers, causing pressure compartmentalization of basinal pore fluids, to forming conduits for up-fault fluid flow. Despite their established importance in controlling the migration and trapping of mineralizing fluids, we have yet to adequately reconcile this duality of flow behavior and its impact on mineral flow systems within basinal sequences from a semiquantitative to quantitative perspective. Combining insights and models derived from earthquake, hydrocarbon, and mineral studies, the principal processes and models for fault-related fluid flow within sedimentary basins are reviewed and a unified conceptual model defined for their role in mineral systems. We illustrate associated concepts with case studies from Irish-type Zn-Pb deposits, sedimentary rock-hosted Cu deposits, and active sedimentary basins. We show that faults can actively affect fluid flow by a variety of associated processes, including seismic pumping and pulsing, or can provide pathways for the upward flow of overpressured fluids or the downward sinking of heavy brines. Associated models support the generation of crustal-scale convective flow systems that underpin the formation of major mineral provinces and provide a basis for differences in the flow behavior of faults, depending on a variety of factors such as fault zone complexities, host-rock properties, deformation conditions, and pressure drives. Flow heterogeneity along faults provides a basis for the thoroughly 3D flow systems that localize fluid flow and lead to the formation of mineral deposits.",
    url = "https://doi.org/10.5382/sp.21.11",
    doi = "10.5382/sp.21.11",
    openalex = "W2948737631",
    references = "doi101144gslsp19870290125"
}

Earth's shallow crust is pervasively breached by fractures and faults that are often filled with saturated clays such as montmorillonite. Pore pressure in montmorillonite is difficult to measure due to its extremely low permeability, resulting in large uncertainties in its friction, which, in turn, may impact our understanding on the mechanical behaviors of the shallow crust. This difficulty motivates us to investigate pore pressure in montmorillonite during frictional sliding. Here we provide a first order understanding on the evolution of pore pressure in montmorillonite during frictional sliding by combining experimental data with an analytical consolidation model. Our result shows large variations in pore pressure in montmorillonite during frictional sliding, which need correction for the evaluation of friction of montmorillonite. We re‐visit this problem with the measured stresses at the end of our slow loading experiments where the modeled pore pressure approaches zero and obtain a new relation that shows a significant cohesive strength. The new relation may be united with our modeled pore pressure with a Biot‐Willis effective stress coefficient of α ∼ 0.5. X‐ray powder diffraction analysis of our samples shows evidence that intense deformation occurred during the frictional sliding with strain‐hardening, consistent with the occurrence of shear localization in the clay matrix following extended frictional sliding (Tembe et al., 2010, https://doi.org/10.1029/2009JB006383). These results suggest that our new relation may represent a constitutive relation for an intensely sheared, saturated montmorillonite in frictional sliding. Our result also suggests that substantial cohesion may appear on some natural clay‐rich faults.

@article{chu2023pore,
    author = "Chu, Chaw‐Long and Wang, Chi‐Yuen",
    title = "Pore Pressure in Montmorillonite During Frictional Sliding",
    year = "2023",
    journal = "Journal of Geophysical Research: Solid Earth",
    abstract = "Earth's shallow crust is pervasively breached by fractures and faults that are often filled with saturated clays such as montmorillonite. Pore pressure in montmorillonite is difficult to measure due to its extremely low permeability, resulting in large uncertainties in its friction, which, in turn, may impact our understanding on the mechanical behaviors of the shallow crust. This difficulty motivates us to investigate pore pressure in montmorillonite during frictional sliding. Here we provide a first order understanding on the evolution of pore pressure in montmorillonite during frictional sliding by combining experimental data with an analytical consolidation model. Our result shows large variations in pore pressure in montmorillonite during frictional sliding, which need correction for the evaluation of friction of montmorillonite. We re‐visit this problem with the measured stresses at the end of our slow loading experiments where the modeled pore pressure approaches zero and obtain a new relation that shows a significant cohesive strength. The new relation may be united with our modeled pore pressure with a Biot‐Willis effective stress coefficient of α ∼ 0.5. X‐ray powder diffraction analysis of our samples shows evidence that intense deformation occurred during the frictional sliding with strain‐hardening, consistent with the occurrence of shear localization in the clay matrix following extended frictional sliding (Tembe et al., 2010, https://doi.org/10.1029/2009JB006383). These results suggest that our new relation may represent a constitutive relation for an intensely sheared, saturated montmorillonite in frictional sliding. Our result also suggests that substantial cohesion may appear on some natural clay‐rich faults.",
    url = "https://doi.org/10.1029/2023jb027601",
    doi = "10.1029/2023jb027601",
    number = "11",
    openalex = "W4388871474",
    volume = "128",
    references = "doi1010029780470172766, doi101016s0012821x03004242, doi101016s0191814102000147, doi101029jb073i006p02225, doi101029jb076i026p06414, doi1010970001069419810100000013, doi101111j1365246x1967tb06218x, doi1011300091761320010290183ulotsz20co2"
}

Gravity is a force contributing to the strain energy and the tectonic stress driving faulting and generating earthquakes. This paper discusses the role of gravity in earthquake mechanics for different tectonic settings. Considering the stress state in normal and reverse tectonic settings, including gravity as a direct contribution to lithostatic load, it is possible to show that earthquakes on normal faults do not have a different energy source than elastic rebound and that this explains differences with reverse faulting earthquakes. The paper discusses the implications from dismissing the elastic rebound theory or limiting its validity to reverse or strike‑slip faulting, as suggested to support the graviquakes model, and the consequences on the mechanics of dip‑slip earthquakes. A simple model of tectonic stress relying on Anderson theory of faulting can describe the different stress state of normal and reverse faulting earthquakes, showing higher values of tectonic stress acting on reverse faults than normal faults, for different values of the static friction coefficient. The model shows that the difference between tectonic stress before and after a dip‑slip earthquake increases with the static friction coefficient, emphasizing the effect of the drained conditions on compressional tectonic stress, and the negligible effect for extensional tectonic settings. Slip can occur on normal faults creating horizontal extensional deformation when the minimum stress is compressional, since extension is caused by the deviatoric stress acting on the fault plane. The different stress state can explain numerous seismological observations, likely accounting for non‑Byerlee friction, stress and strength heterogeneity and geometrical complexity. The adoption of elastic rebound does not imply that the energetics of normal and reverse faulting earthquakes is the same. Considering crustal faults as passive subjects accommodating slip caused by volume collapse contradicts geological observations of fault zone structure, laboratory experiments and the spectrum of fault slip behavior. Faults are active geological subjects characterizing the strain localization and the energy release.

@article{cocco2025the,
    author = "Cocco, Massimo",
    title = "The role of gravity in normal and reverse faulting earthquakes",
    year = "2025",
    journal = "Annals of Geophysics",
    abstract = "Gravity is a force contributing to the strain energy and the tectonic stress driving faulting and generating earthquakes. This paper discusses the role of gravity in earthquake mechanics for different tectonic settings. Considering the stress state in normal and reverse tectonic settings, including gravity as a direct contribution to lithostatic load, it is possible to show that earthquakes on normal faults do not have a different energy source than elastic rebound and that this explains differences with reverse faulting earthquakes. The paper discusses the implications from dismissing the elastic rebound theory or limiting its validity to reverse or strike‑slip faulting, as suggested to support the graviquakes model, and the consequences on the mechanics of dip‑slip earthquakes. A simple model of tectonic stress relying on Anderson theory of faulting can describe the different stress state of normal and reverse faulting earthquakes, showing higher values of tectonic stress acting on reverse faults than normal faults, for different values of the static friction coefficient. The model shows that the difference between tectonic stress before and after a dip‑slip earthquake increases with the static friction coefficient, emphasizing the effect of the drained conditions on compressional tectonic stress, and the negligible effect for extensional tectonic settings. Slip can occur on normal faults creating horizontal extensional deformation when the minimum stress is compressional, since extension is caused by the deviatoric stress acting on the fault plane. The different stress state can explain numerous seismological observations, likely accounting for non‑Byerlee friction, stress and strength heterogeneity and geometrical complexity. The adoption of elastic rebound does not imply that the energetics of normal and reverse faulting earthquakes is the same. Considering crustal faults as passive subjects accommodating slip caused by volume collapse contradicts geological observations of fault zone structure, laboratory experiments and the spectrum of fault slip behavior. Faults are active geological subjects characterizing the strain localization and the energy release.",
    url = "https://doi.org/10.4401/ag-9445",
    doi = "10.4401/ag-9445",
    number = "6",
    openalex = "W4416912680",
    pages = "S689",
    volume = "68"
}