The Coulomb critical taper theory applied to gravitational instabilities

Mourgues, R.; Lacoste, Aurélien; Garibaldi, Cynthia

doi:10.1002/2013jb010359

Cited by 19 publications

(13 citation statements)

References 48 publications

(112 reference statements)

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“…In our numerical models we observe shallow gravity instabilities /similar to slope aprons/ for simulations in mechanical modes II and III. This result is consistent with the prediction of Mourgues et al (). In their analysis, they use the concept of the safety factor (

F S = \tan false(α false) false/ \tan false(α_{m a x} false)

) often used in engineering and which varies very similarly to

\overset{α}{true}

.…”

Section: Discussionsupporting

confidence: 94%

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Control of Fault Weakening on the Structural Styles of Underthrusting‐Dominated Non‐Cohesive Accretionary Wedges

2020

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Underthrusting is a typical process at compressive margins responsible for nappe stacking and sediment subduction. In nature, underthrusting is often associated with weak basal faults, although static mechanical analysis (critical taper theory) suggests that weak basal faults promote accretion while strong basal faults promote underthrusting. We perform mathematical analyses and numerical simulations to determine whether permanent fault weakening promotes or inhibits underthrusting. We investigate the control of permanent fault weakening on the dynamics of a strong‐based ( false(1−λb*false)μb≈false(1−λ*false)μ) non‐cohesive wedge ( μ and μb are internal and basal friction, respectively). We control the wedge material strength by a spatially constant fluid overpressure factor ( λ*), and fault strength by a plastic strain weakening factor ( χ). First, we use the critical taper theory to determine a mechanical mode diagram that predicts structural styles. Then, we perform numerical simulations of accretionary wedge formation to establish their dynamical structural characteristics. We determine a continuum of structural styles between three end‐members which correspond to the theoretical mechanical mode transitions. Style 1 is characterized by thin tectonic slices and little to no underthrusting. Style 2 shows thick slices, nappe stacking, and shallow gravity‐driven tectonics. Style 3 displays the complete underthrusting of the incoming sediments, that are exhumed when they reach the backstop. We conclude that in the condition of an initially strong wedge base, permanent fault weakening promotes underthrusting. Thus, this contribution enlightens the control of the dynamic evolution of material properties on the formation of subduction channels, slope instabilities, and antiformal nappe stacks.

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F S = \tan false(α false) false/ \tan false(α_{m a x} false)

) often used in engineering and which varies very similarly to

\overset{α}{true}

.…”

Section: Discussionsupporting

confidence: 94%

“…When those numbers are close to 1, shallow gravity sliding occurs. When

F S

\overset{α}{true}

decreases, Mourgues et al () suggest that deep normal faults reaching the décollement are expected. This theoretical prediction is consistent with the transition that we observe from shallow gravity sliding in Style 2 to deep normal faulting in Style 3.…”

Section: Discussionmentioning

confidence: 99%

Control of Fault Weakening on the Structural Styles of Underthrusting‐Dominated Non‐Cohesive Accretionary Wedges

2020

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“…The lower boundary of this domain corresponds to the stability limit of accretionary wedges in the compressive regime. Of more interest here is the upper boundary of the grey domain corresponding to gravity instability (Mourgues et al 2014). This upper limit is very close to our predictions (dash-dotted curve) for β larger than 25…”

Section: Stability Conditionssupporting

confidence: 85%

Reappraisal of gravity instability conditions for offshore wedges: consequences for fluid overpressures in the Niger Delta

Yuan¹,

Leroy²,

Maillot³

2016

Geophys. J. Int.

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S U M M A R YGravity instabilities in offshore deltas often involve three structural domains in interaction by the weak detachment plane: an upslope extensional region, a transitional domain sliding seaward, and a downslope compressive region. We provide the fluid pressure conditions for the gravity instabilities due to the interaction of these three structural domains. For that purpose, we apply the kinematic approach of Limit Analysis which relies on the mechanical equilibrium and on the assumption that the onset of the instability is indeed triggered by the motion of the three domains if the Coulomb criterion is met on all slipping faults. The Limit Analysis predictions include the detachment activation length and the normal and thrust fault dips for any given topographic profile. The approach is validated by showing that our predictions match the experimental results on normal faulting triggered by air overpressure in sand analogues. For offshore wedges, the stabilizing effect of the frontal thrusting and of the transitional zone sliding requires large overpressures to reduce friction within the detachment and upslope sediment deposition to trigger the instability. As a consequence, the topographic slope is found to be several degrees larger than predicted with the Critical Coulomb Wedge (CCW) theory which does not account for the interaction of the three domains. The difference in predictions between the two theoretical approaches is important for length ratio less than 100, defined by the ratio of the detachment activated length to the downslope sediment thickness. Fitting our prototype to the offshore Niger Delta and estimating the above length ratio to be in the range of 30-70, it is found that, for cohesionless materials, the effective friction coefficient μ B is less than 0.27 within the bulk material and μ D is less than 0.017 in the detachment for the gravity instability to occur. These values are lower than those previously determined (μ B = 0.5−0.9, μ D = 0. − 0.2) by considering only the compressive domain and applying the CCW theory. These new values correspond to a pore-fluid pressure in the range of 80-90 per cent of the lithostatic pressure within the bulk material (Hubbert-Rubey fluid-pressure ratio 0.8-0.9), and in the range of 97-99 per cent of the lithostatic pressure within the detachment.Key words: Geomechanics; Sedimentary basin processes; Dynamics and mechanics of faulting; Dynamics: gravity and tectonics; Mechanics, theory, and modeling; Africa. I N T RO D U C T I O NRegional seismic studies across the Amazon Fan (Silva et al. 1998;Cobbold et al. 2004), the offshore Niger Delta (Weber & Daukoru 1975;Hooper et al. 2002;Maloney et al. 2010), and the offshore Brunei wedge (Tingay et al. 2009;King et al. 2010) show normal faulting in the thick, coastal part on the shelf and simultaneous thrusting in the thin, deep part, with all faults rooted on a common detachment level. These structures are thus typically characterized by three successive domains above the weak detachment: the upslope e...

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“…It complements the derivation found in Wang et al [2006] and Mourgues et al [2014], by providing the complete expression of the implicit solution in terms of the critical taper + as function of the fluid overpressures and friction angles. This expression is valid for any permissible value of the slopes and , thus the proposed name ECCW theory.…”

Section: Appendix A: Different Fluid Pressure Parametrizationsmentioning

confidence: 65%

“…The solution in the last two references is nevertheless approximate in the sense that its validity is limited to low topographic slopes and pore pressures. It is only recently that the CCW theory was amended by Wang et al [2006] to produce an exact solution (called the exact critical Coulomb wedge (ECCW) theory in this contribution) that was applied to sandbox experiments [Mourgues et al, 2014].…”

Section: Introductionmentioning

confidence: 99%

Tectonic and gravity extensional collapses in overpressured cohesive and frictional wedges

2015

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Two modes of extensional collapse in a cohesive and frictional wedge of arbitrary topography, finite extent, and resting on an inclined weak décollement are examined by analytical means. The first mode consists of the gravitational collapse by the action of a half-graben, rooting on the décollement and pushing seaward the frontal part of the wedge. The second mode results from the tectonics extension at the back wall with a similar half-graben kinematics and the landward sliding of the rear part of the wedge. The predictions of the maximum strength theorem, equivalent to the kinematic approach of limit analysis and based on these two collapse mechanisms, not only match exactly the solutions of the critical Coulomb wedge theory, once properly amended, but generalizes them in several aspects: wedge of finite size, composed of cohesive material and of arbitrary topography. This generalization is advantageous to progress in our understanding of many laboratory experiments and field cases. For example, it is claimed from analytical results validated by experiments that the stability transition for a cohesive, triangular wedge occurs with the activation of the maximum length of the décollement. It is shown that the details of the topography, for the particular example of the Mejillones peninsula (North Chile) is, however, responsible for the selection of a short length-scale, dynamic instability corresponding to a frontal gravitational instability. A reasonable amount of cohesion is sufficient for the pressures proposed in the literature to correspond to a stability transition and not with a dynamically unstable state.

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The Coulomb critical taper theory applied to gravitational instabilities

Cited by 19 publications

References 48 publications

Control of Fault Weakening on the Structural Styles of Underthrusting‐Dominated Non‐Cohesive Accretionary Wedges

Control of Fault Weakening on the Structural Styles of Underthrusting‐Dominated Non‐Cohesive Accretionary Wedges

Reappraisal of gravity instability conditions for offshore wedges: consequences for fluid overpressures in the Niger Delta

Tectonic and gravity extensional collapses in overpressured cohesive and frictional wedges

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