Conditions for earthquake surface rupture along the San Andreas Fault System, California

Streit, Jürgen E.

doi:10.1029/1999jb900131

Cited by 13 publications

(4 citation statements)

References 54 publications

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“…The oblique lines give the pore fluid factors required to reactivate the N130 • E seismic fault for different values of the coefficient of static friction and for different values of differential stresses. Based on stress measurements in deep boreholes (Streit 1999 ; table 1), the value of the differential stress at a depth of 7 km can be estimated at 110 ± 10 MPa.…”

Section: Pore Fluid Pressure Excess Required For Reactivation During mentioning

confidence: 99%

Reactivation of a strike-slip fault by fluid overpressuring in the southwestern French-Italian Alps

Leclère

Fabbri

Daniel³

et al. 2012

Geophysical Journal International

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International audienceA crustal-scale N130°E strike-slip fault in the Ubaye-Argentera area, southwestern French-Italian Alps, was the locus of a seismic swarm in 2003-2004. Its reactivation is examined by a 2-D frictional fault analysis. The regional stress tensor in the vicinity of the fault is determined by inversion of focal mechanisms of the 38 events with largest magnitudes of the 2003-2004 swarm. Inversion shows that the axis of the maximum principal stress σ1 is oriented nearly horizontal and at 63° from the fault plane and that the intermediate principal stress σ2 is almost parallel to the fault plane. A 2-D analysis with a static coefficient of friction of 0.4 (consistent with the presence of phyllosilicate-rich gouges at depth) shows that the N130°E fault is unfavourably oriented and that its reactivation is possible only with pore fluid pressure excess in the hypocentral region (6-7 km below surface). A calculation based on a pore fluid factor-differential stress failure mode diagram shows that the required excess pressure is comprised between 7 and 26 MPa. The presence of thermal springs in the Argentera area indicates that the pore fluid is water. The pore water overpressure is likely achieved by fault zone compaction and hydraulic barriers. The hydraulic barriers can be provided by hydrothermal sealing of the fault damage zone and by the 1-2-km-thick sedimentary lid (marl-rich autochtonous sedimentary cover and Embrunais-Ubaye sedimentary nappes) whose permeability is lower than that of the underlying crystalline rock

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Section: Pore Fluid Pressure Excess Required For Reactivation During mentioning

confidence: 99%

Reactivation of a strike-slip fault by fluid overpressuring in the southwestern French-Italian Alps

Leclère

Fabbri

Daniel³

et al. 2012

Geophysical Journal International

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“…The major improvement of our analysis over previous studies of fault reactivation is the minimum constraints we impose on the parameters that control fault reactivation. Indeed, we only assume that (1) one of the principal stress axes is vertical, in agreement with Hurd and Zoback (), (2) the crust is fully saturated with hydrostatic pore fluid pressure, as justified in Townend and Zoback (), and (3) differential stress increases linearly with depth (Streit, ). We assume a homogeneous stress field and do not account for the static stress changes associated to large earthquakes such as those of the 1811–1812 New Madrid sequence (Mueller et al., ), as their calculation would be too uncertain given the available information.…”

Section: Description Of the Parametric Analysismentioning

confidence: 86%

“…We assume the differential stress σ D to increase linearly with depth and test three values of its vertical gradient k derived from borehole stress measurements (Quinones et al., ; Streit, ): a lower bound value of 10 MPa/km, an intermediate value of 15 MPa/km, and an upper bound value of 20 MPa/km. The thin black lines on each panel of Figure represents the linear evolution of the differential stress σ D with depth for these three values of k .…”

Section: Description Of the Parametric Analysismentioning

confidence: 99%

A Parametric Analysis of Fault Reactivation in the New Madrid Seismic Zone: The Role of Pore Fluid Overpressure

Leclère

Calais

2019

JGR Solid Earth

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Earthquakes in Stable Continental Regions (SCR), where localized present-day tectonic loadingis negligible, remain difficult to explain. The New Madrid Seismic Zone (NMSZ) is a type-locale for such events, with four M>7 events in 1811-1812 and a regional seismicity that continues to this day. Here, we seek to determine the most favorable conditions for fault reactivation in such a context using 33 earthquakes in the 2.1-4.7 magnitude range with well-determined focal mechanisms while accounting for the vertical gradient of differential stress with depth. To do so, we developed a Mohr-Coulomb-based parametric analysis of fault reactivation that allows us to vary the orientation of the principal stresses, the shape ratio of the stress tensor, the fault friction coefficient, the pore fluid overpressure, and the gradient of differential stress with depth. Doing so, we are able to determine the lowest stress perturbation conditions required for fault reactivation. Our results show that the reactivation of the faults studied here requires pore fluid overpressure, unless their friction coefficient is 0.4 or less. We argue that such weak faults are unlikely and favor a triggering mechanism via deep fluids, possibly upwelling from the upper mantle where a low-velocity seismic anomaly could indicate their presence. This mechanism, documented in other intraplate areas, does not require local tectonic stress or strain accumulation to explain seismicity in active intraplate regions, where elastic strain is drawn from a prestressed crust.

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“…Where tensile strength exists, tensile failure can occur under low differential stress conditions (σ 1 -σ 3 < 4T), while mixed mode extensional shear fractures form at differential stresses intermediate to tensile and shear failure (4T-6T) using a Griffith-Coulomb failure envelope. In general, many instances of fracture-induced top seal failure have been ascribed to tensile failure as a result of pore pressure reducing the minimum effective stress beneath rock tensile strength 4,32 . However, in fault zones, reactivation in tension can only occur when faults have become severely misoriented for shear reactivation with respect to the stress field or when such faults have regained cohesive strength due to cementation 22,31 .…”

Section: Strong Faultsmentioning

confidence: 99%

Geomechanical Fault Characterization: Impact on Quantitative Fault Seal Risking

Jones¹,

Dewhurst²,

Hillis³

et al. 2002

Proceedings of SPE/ISRM Rock Mechanics Conference

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractFault sealing is one of the key factors controlling hydrocarbon accumulations and can be a significant influence on reservoir behavior during production. Fault seal is, therefore, a major exploration and production uncertainty that requires a rigid, systematic framework within which to quantify the geological risk of trapping hydrocarbons. One of the key uncertainties in this risking procedure is the breaching of structurally bound traps due to the formation of structural permeability networks. Considering a population of faults and fractures, those that are critically stressed are more prone to act as conduits for fluid transmission. Evaluation and mapping of fault seal breach through such networks involves integration of in-situ stress conditions, pore pressure, fault architecture and fault geomechanics.Geomechanical characterization of well-lithified fault rocks from the Otway Basin and the Northwest Shelf demonstrates that faults can exhibit significant cohesive strength and that fault reactivation and trap breach is influenced by the development of shear, tensile and mixedmode fractures. The mechanics of the reactivation process are influenced by grain strength and fault morphology. Mercury injection capillary pressures of cataclastic faults indicate a seal capacity of 2400 psi. Following reactivation, seal capacity is reduced ~95% due to the development of a highly connected fracture network. The tensile strength of such healed faults allows failure to occur by shear, tensile and mixed mode fracturing. These data suggest simple application of Byerlee's Law may not always be applicable when predicting reactivation induced fault seal failure. Consequently, geomechanical tools used to predict trap breach via reactivation that assume cohesionless frictional failure are likely to significantly underestimate seal reactivation risk.The impact of structurally risking traps using Byerlee and laboratory-derived fault data is demonstrated using the Fault Seal Risk Web approach. Application of geomechanical fault data results in a significant reappraisal of prospect structural risk due to consideration of fault healing.

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Conditions for earthquake surface rupture along the San Andreas Fault System, California

Cited by 13 publications

References 54 publications

Reactivation of a strike-slip fault by fluid overpressuring in the southwestern French-Italian Alps

Reactivation of a strike-slip fault by fluid overpressuring in the southwestern French-Italian Alps

A Parametric Analysis of Fault Reactivation in the New Madrid Seismic Zone: The Role of Pore Fluid Overpressure

Geomechanical Fault Characterization: Impact on Quantitative Fault Seal Risking

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