Seismic hazard of the western Makran subduction zone: Insight from mechanical modelling and inferred frictional properties

Pajang, Sepideh; Cubas, Nadaya; Letouzey, J.; Pourhiet, Laëtitia Le; Seyedali, Seyedmohsen; Fournier, Marc; Agard, Philippe; Khatib, Mohammad Mahdi; Heyhat, Mahmoudreza; Mokhtari, Mohammad

doi:10.1016/j.epsl.2021.116789

Cited by 29 publications

(27 citation statements)

References 48 publications

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“…The relationship between the forearc wedge morphology and the seismogenic behavior has been attributed to spatial variations of basal shear strength (Song and Simons, 2003) and forearc basins are generally associated with an extremely low effective friction within the seismogenic zone (µ ≤ 0.05) (Cubas et al, 2013;Pajang et al, 2021a), which is also supported by heat flow measurements and thermal modeling (Gao and Wang, 2014).…”

Section: Introductionmentioning

confidence: 86%

The topographic signature of temperature-controlled rheological transitions in an accretionary prism

2022

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Abstract. The local topographic slope of the accretionary prism is often used together with the critical taper theory to determine the effective friction on subduction megathrust. In this context, extremely small topographic slopes associated with extremely low effective basal friction (μ≤0.05) can be interpreted either as seismically locked portions of megathrust, which deforms episodically at dynamic slip rates or as a viscously creeping décollement. Existing mechanical models of the long-term evolution of accretionary prism, sandbox models, and numerical simulations alike, generally do not account for heat conservation nor for temperature-dependent rheological transitions. Here, we solve for advection–diffusion of heat with imposed constant heat flow at the base of the model domain. This allows the temperature to increase with burial and therefore to capture how the brittle–ductile transition and dehydration reactions within the décollement affect the dynamic of the accretionary prism and its topography. We investigate the effect of basal heat flow, shear heating, thermal blanketing by sediments, and the thickness of the incoming sediments. We find that while reduction of the friction during dewatering reactions results as expected in a flat segment often in the forearc, the brittle–ductile transition results unexpectedly in a local increase of topographic slope by decreasing internal friction. We show that this counterintuitive backproduct of the numerical simulation can be explained by the onset of internal ductile deformation in between the active thrusts. Our models, therefore, imply significant viscous deformation of sediments above a brittle décollement, at geological rates, and we discuss its consequences in terms of interpretation of coupling ratios at subduction megathrust. We also find that, with increasing burial and ductile deformation, the internal brittle deformation tends to be accommodated by backthrusts until the basal temperature becomes sufficient to form a viscous channel, parallel to the décollement, which serves as the root to a major splay fault and its backthrust and delimits a region with a small topographic slope. Morphologic resemblances of the brittle–ductile and ductile segments with forearc high and forearc basins of accretionary active margins, respectively, allow us to propose an alternative metamorphic origin of the forearc crust in this context.

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Section: Introductionmentioning

confidence: 86%

The topographic signature of temperature-controlled rheological transitions in an accretionary prism

2022

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“…Our simple models permit us to understand first order mechanisms in forearc formation, but improvements are still needed to better understand how the brittle-ductile transition affects the formation of splay faults providing an alternative model to the formation of forearc basins as well as an alternative origin for the forearc crust. We find that, the drop in friction between the ductile and brittle part of the accretionary prism and smectite to illite dehydration reaction is not sufficient to explain the normal faults observed along some accretionary margins like Chile or Makran Cubas et al (2013); Pajang et al (2021). This result leads us to conclude that the normal faults arise from phenomena we neglected in our simplified approach.…”

Section: Limitations and Perspectivesmentioning

confidence: 77%

“…The relationship between the fore-arc wedge morphology and the seismogenic behavior has been attributed to spatial variations of basal shear strength (Song and Simons, 2003) and fore-arc basins are generally associated with an extremely low effective friction along the seismogenic zone (µ ≤ 0.05) (Cubas et al, 2013;Pajang et al, 2021), which is also supported by heat flow measurements and thermal modeling (Gao and Wang, 2014).…”

Section: Introductionmentioning

confidence: 79%

“…Along seismically active accretionary prisms, an increase of topographic slope and decrease in apparent geodetic coupling are interpreted as the down-dip limit of the seismogenic zone (Cubas et al, 2013). In the first case, the rise in topographic slope indicates an increase of effective basal friction which corresponds to the down-dip end of dominant seismic slip (Cubas et al, 2013;Pajang et al, 2021). In the second case, geodetic deformation at velocities that differs from subducting plate velocities is generally interpreted as a lack of coupling on the plate interface based on elastic models (Perfettini et al, 2010;Chlieh et al, 2008).…”

Section: Up and Down-dip End Of The Seismogenic Zonementioning

confidence: 99%

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The topographic signature of temperature controlled rheological transitions in an accretionary prism

Pajang

Pourhiet

Cubas

2021

Preprint

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Abstract. The local topographic slope of the accretionary prism is often used together with the critical taper theory to determine the effective friction on subduction megathrust. In this context, extremely small topographic slopes associated with extremely low effective basal friction (μ ≤ 0.05) can be interpreted either as seismically locked portions of megathrust, which deforms episodically at dynamic slip rates or as a viscously creeping décollement. Existing mechanical models of the long-term evolution of accretionary prism, sandbox models, and numerical simulations alike, generally do not account for heat conservation nor for temperature dependant rheological transitions. Here, we solve for advection-diffusion of heat with imposed constant heat flow at the base of the model domain. This allows the temperature to increase with burial, and therefore to capture how the brittle-ductile transition and dehydration reactions within the décollement affect the dynamic of the accretionary prism and its topography. We investigate the effect of basal heat flow, shear heating, thermal blanketing by sediments, the thickness of the incoming sediments. We find that while reduction of the friction during dewatering reactions result as expected in a flat segment often in the fore-arc, the brittle-ductile transition result unexpectedly in a local increase of topographic slope. We show that this counter-intuitive backproduct of the numerical simulation can be explained and by the onset of internal ductile deformation in between the active thrusts. Our models, therefore, implies significant viscous deformation of sediments above a brittle décollement, at geological rates, and we discuss its consequences in term of interpretation of coupling ratios at subduction megathrust. We also find that, with increasing burial and ductile deformation, the internal brittle deformation tends to be accommodated by backthrusts until the basal temperature becomes sufficient to form a viscous channel, parallel to the décollement, which serves as root to a major splay fault and its back-thrust and delimits a region with small topographic slope. Morphologic resemblances of the brittle-ductile and ductile segments with fore-arc high and fore-arc basins of accretionary active margins respectively allow us to propose an alternative metamorphic origin of the fore-arc crust in this context.

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“…Studies of effective friction in accretionary wedges worldwide typically display values of thrust faults' effective friction as low as 0.1°(e.g. Pajang et al, 2021). At the larger scale of subduction plate tectonics, numerical models also require effective frictions sometimes as low as 0.1°in order to fit observations, such as for instance along the Chilean subduction zone on the scale of several Myr (e.g.…”

Section: Frictional Strengthmentioning

confidence: 99%

The interplay of a fault zone and a volcanic reservoir from 3D elasto-plastic models: Rheological conditions for mutual trigger based on a field case from the Andean Southern Volcanic Zone

Ginouves

Gerbault

Cembrano

et al. 2021

Journal of Volcanology and Geothermal Research

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Seismic hazard of the western Makran subduction zone: Insight from mechanical modelling and inferred frictional properties

Cited by 29 publications

References 48 publications

The topographic signature of temperature-controlled rheological transitions in an accretionary prism

The topographic signature of temperature-controlled rheological transitions in an accretionary prism

The topographic signature of temperature controlled rheological transitions in an accretionary prism

The interplay of a fault zone and a volcanic reservoir from 3D elasto-plastic models: Rheological conditions for mutual trigger based on a field case from the Andean Southern Volcanic Zone

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