Localization of intraplate deformation through fluid-assisted faulting in the lower-crust: The Flinders Ranges, South Australia

Balfour, N.; Cummins, Phil R.; Pilia, Simone; Love, David W.

doi:10.1016/j.tecto.2015.05.014

Cited by 22 publications

(18 citation statements)

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“…Therefore, a likely explanation for the Botswana earthquake is that it was triggered by elevated, sublithostatic, pore fluid pressure that enabled failure at the low differential stress that prevails in the viscous lower crust (Gold & Soter, 1985). The observed foreshock swarm-like sequences may be the signature of the initiation of a pulse of high pore fluid pressure (Balfour et al, 2015;Hainzl & Fischer, 2002;Reyners et al, 2007). Field observations show numerous evidence of fluid-assisted embrittlement in the viscous regime of deformation (Handy et al, 2007;Wehrens et al, 2016).…”

Section: What Caused the Botswana Earthquake?mentioning

confidence: 99%

The April 2017 M_w6.5 Botswana Earthquake: An Intraplate Event Triggered by Deep Fluids

Gardonio

Jolivet

Calais

et al. 2018

Geophysical Research Letters

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Large earthquakes in stable continental regions remain puzzling as; unlike at plate boundaries, they do not result from the local buildup of strain driven by plate tectonics. The 2017 Mw6.5, Bostwana normal faulting earthquake occurred in a region devoid from recent tectonic activity and where present‐day deformation is negligible. The depth of the event (29 ± 4 km), in a felsic lower crust where ductile deformation is expected, likely requires a transient pulse of fluids from a deep source to activate brittle faulting. The mainshock was preceded by two foreshock swarm‐like sequences that may be further evidence for fluid movement in a critically loaded fault network. Contrary to plate boundary events, the Mw6.5 Botswana earthquake did not require prior localized stress or strain accumulation. We propose that the crust in stable continental regions, even long after the last tectonic episode, constitutes a reservoir of elastic stress that can be released episodically, for instance, as a result of deep fluid migration.

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Section: What Caused the Botswana Earthquake?mentioning

confidence: 99%

The April 2017 M_w6.5 Botswana Earthquake: An Intraplate Event Triggered by Deep Fluids

Gardonio

Jolivet

Calais

et al. 2018

Geophysical Research Letters

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“…As a result, the Flinders Ranges are seismically active (Figure ), mainly in the top 20 km of the crust. However, deeper earthquake epicenters to depths of 30 km are present and have been reported in the central and southern Flinders Ranges [ Balfour et al , ]. Seismicity is lower across the survey area compared to the central and southern Flinders Ranges, suggesting that the increased deformation there is possibly due to a higher abundance of preexisting crustal faults.…”

Section: Results and Interpretationmentioning

confidence: 80%

“…Beneath the Newer Volcanic Province, low resistivity in the lower crust and upper mantle is a result of recent decompressional melting within a lithospheric step [ Aivazpourporgou et al , ]. Recently, long‐period MT data of the regional AusLAMP deployment revealed wide‐spread lower crustal conductance across the Flinders and Curnamona Province [ Robertson et al , ], also in areas to the south where seismicity is even higher than in the current survey area [ Balfour et al , ]. It is likely that any crustal fluid flux leaves an imprint by means of precipitation of sulphides, magnetite, or graphite along grain boundaries under preferable and stable redox conditions [ Nover et al , ; Thiel et al , ].…”

Section: Results and Interpretationmentioning

confidence: 99%

“…Given the connection between fluid pathways and enhanced strain/seismicity (Figure ), Balfour et al [] conclude that seismicity is fluid‐assisted and that the deep earthquakes require pore pressure close to lithostatic. The fault dips of crustal earthquakes average around 40°, skewed to steeper angles [ Balfour et al , ] and are therefore steeper than newly formed thrust faults in a brittle regime [ Sibson , ].…”

Section: Results and Interpretationmentioning

confidence: 99%

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Conductivity response to intraplate deformation: Evidence for metamorphic devolatilization and crustal‐scale fluid focusing

Thiel

Soeffky

Krieger

et al. 2016

Geophysical Research Letters

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We present two‐dimensional electrical resistivity models of two 40 km magnetotelluric (MT) profiles across the Frome Embayment to the east of the northern Flinders Ranges, South Australia. The lower crust shows low resistivity of 10 Ω m at around 30 km depth. The middle crust is dominated by resistive (>1000 Ω m) basement rocks underlying the Flinders Ranges. Adjacent to the ranges, conductive lower crust is connected to vertical zones of higher conductivity extending to just below the brittle‐ductile transition at ∼10 km depth. The conductive zones narrow in the brittle upper crust and dip at roughly 45° beneath the surface. Zones of enhanced conductivity coincide with higher strain due to topographic loading and sparse seismicity. We propose that fluids are generated through neotectonic metamorphic devolatilization. Low‐resistivity zones display areas of fluid pathways along either preexisting faults or an effect of crustal compression leading to metamorphic fluid generation. The lower crustal conductors are responding to long‐wavelength flexure‐induced strain, while the upper crustal conductors are responding to short wavelength faulting in the brittle regime. MT is a useful tool for imaging crustal strain in response to far‐field stresses in an intraplate setting and provides important constraints for geodynamic modeling and crustal rheology.

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“…The Reelfoot rift and the major faults composing the NMSZ (NMN, RF, and CWG) may act as preferential pathways for deep fluids, as documented in Vogtland/western Bohemia, where mantle fluid upwellings and seismicity are localized near the crossing between the Eger rift and the Mariánské Lazné fault (Bräuer et al., ; Weise et al., ). Such deep fluids may be metamorphic in origin, for instance, brine water in equilibrium with the granitic basement rocks (Bräuer et al., ; Mittempergher et al., ), or mantle fluids such as documented along some intraplate faults (Balfour et al., ; Kennedy & Soest, ). Seismic tomography from surface waves as well as P and S body waves show a pronounced low‐velocity anomaly in the upper mantle beneath the NMSZ extending down to 200–250 km (Chen et al., ; Nyamwandha et al., ; Pollitz & Mooney, ).…”

Section: Discussionmentioning

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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Localization of intraplate deformation through fluid-assisted faulting in the lower-crust: The Flinders Ranges, South Australia

Cited by 22 publications

References 58 publications

The April 2017 M_w6.5 Botswana Earthquake: An Intraplate Event Triggered by Deep Fluids

The April 2017 M_w6.5 Botswana Earthquake: An Intraplate Event Triggered by Deep Fluids

Conductivity response to intraplate deformation: Evidence for metamorphic devolatilization and crustal‐scale fluid focusing

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

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Localization of intraplate deformation through fluid-assisted faulting in the lower-crust: The Flinders Ranges, South Australia

Cited by 22 publications

References 58 publications

The April 2017 Mw6.5 Botswana Earthquake: An Intraplate Event Triggered by Deep Fluids

The April 2017 Mw6.5 Botswana Earthquake: An Intraplate Event Triggered by Deep Fluids

Conductivity response to intraplate deformation: Evidence for metamorphic devolatilization and crustal‐scale fluid focusing

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

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The April 2017 M_w6.5 Botswana Earthquake: An Intraplate Event Triggered by Deep Fluids

The April 2017 M_w6.5 Botswana Earthquake: An Intraplate Event Triggered by Deep Fluids