Coseismic ultramylonites: An investigation of nanoscale viscous flow and fault weakening during seismic slip

Pozzi, Giacomo; Paola, N. De; Holdsworth, R. E.; Bowen, Leon; Nielsen, S. B.; Dempsey, Edward D.

doi:10.1016/j.epsl.2019.03.042

Cited by 40 publications

(79 citation statements)

References 47 publications

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“…interpreted to represent MSSs. The matured PSZ is observed to consist of 200-300 nm sized, polygonal grains characterized by a crystallographic preferred orientation [123]. Returning to patchy MSSs formed in LVF experiments using calcite gouge (v = 10 −6 m/s, σn eff = 50 MPa, ∑x ≈ 5-6 mm), individually these show remarkable micro-and nanostructural characteristics (Figure 6a-d) [140].…”

Section: Nanocrystalline Principal Slip Zones Formed In Fault-slip Exmentioning

confidence: 96%

Section: Nanocrystalline Principal Slip Zones Formed In Fault-slip Exmentioning

confidence: 99%

“…Electron backscatter diffraction is a powerful tool frequently used to quantify a CPO [121], however, to our knowledge this remains difficult to apply to extremely fine-grained aggregates such as those characterizing nanocrystalline PSZs (grain size << 100 nm). Recently, EBSD measurements were used to quantify a CPO characterizing a PSZ composed of 200-300 nm-sized, polygonal grains, formed in simulated calcite gouge sheared in HVF tests [122,123]. Mirror-Slip Surfaces in Principal Slip Zones Developed in Calcite Gouge "Glossy", "shiny", or "mirror-like" slip surfaces (MSSs) have been observed in experiments using a wide range of sample materials, characterized by a wide range of normal stresses (σ n ), displacement rates (v), and cumulative displacements ( x) (Table 2) ( Figures 5 and 6).…”

Section: Nanocrystalline Principal Slip Zones Formed In Fault-slip Exmentioning

confidence: 99%

“…Using polished sections prepared normal to the slip vector they observed that, after an initial stage of slip (Σx ≈ 7 cm), sharp discontinuities develop which are interpreted to represent MSSs. The matured PSZ is observed to consist of 200-300 nm sized, polygonal grains characterized by a crystallographic preferred orientation [123].…”

Section: Nanocrystalline Principal Slip Zones Formed In Fault-slip Exmentioning

confidence: 99%

“…Aside from the formation of nanocrystallites and amorphization within a PSZ, this does not explain the development of an internal CPO. Pozzi et al [123] suggested that grain-size insensitive (GSI) creep mechanisms (dislocation creep) may explain CPO formation in a PSZ composed of 200-300 nm-sized grains formed in calcite gouge sheared at v = 1.4 m/s, at σ n = 25 MPa. However, in the case of CPO-bearing PSZs formed in LVF tests, the porous structure observed in the bulk PSZ ( Figure 6) is suggestive of nanogranular flow, which is not known for generating, or retaining a pre-existing, CPO.…”

Section: Formation Of Psz Nanostructures Amorphous Materials and Cpomentioning

confidence: 99%

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Nanocrystalline Principal Slip Zones and Their Role in Controlling Crustal Fault Rheology

2019

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Principal slip zones (PSZs) are narrow (<10 cm) bands of localized shear deformation that occur in the cores of upper-crustal fault zones where they accommodate the bulk of fault displacement. Natural and experimentally-formed PSZs consistently show the presence of nanocrystallites in the <100 nm size range. Despite the presumed importance of such nanocrystalline (NC) fault rock in controlling fault mechanical behavior, their prevalence and potential role in controlling natural earthquake cycles remains insufficiently investigated. In this contribution, we summarize the physical properties of NC materials that may have a profound effect on fault rheology, and we review the structural characteristics of NC PSZs observed in natural faults and in experiments. Numerous literature reports show that such zones form in a wide range of faulted rock types, under a wide range of conditions pertaining to seismic and a-seismic upper-crustal fault slip, and frequently show an internal crystallographic preferred orientation (CPO) and partial amorphization, as well as forming glossy or "mirror-like" slip surfaces. Given the widespread occurrence of NC PSZs in upper-crustal faults, we suggest that they are of general significance. Specifically, the generally high rates of (diffusion) creep in NC fault rock may play a key role in controlling the depth limits to the seismogenic zone.In this paper, we aim to elucidate the significance of nanocrystalline PSZs in Earth's upper crust. We start with background on fault mechanics and upper-crustal seismogenesis, and summarize some key physical properties of nanophase materials which, when applied to fault rock, are expected to be of major importance in controlling fault strength and stability. We go on to review the micro-and nanostructural characteristics of natural and experimentally-formed nanocrystalline PSZs, and list reports from the literature of PSZs characterized by grains <100 nm in size. Our work demonstrates that nanocrystalline PSZs form under a wide range of conditions pertaining slow (a-seismic) and fast (co-seismic) upper-crustal fault slip. Also, we observe that they are frequently characterized by an internal crystallographic preferred orientation, and by the presence of amorphous materials and/or glossy fault plane interfaces known as "mirror-slip" surfaces. Given the abundant observations of nanocrystalline PSZs in field exposures of faults, as well as in experiments, we suggest that they are of general importance to upper-crustal fault deformation. The physical properties of nanocrystalline fault rock may play a key role in natural earthquake cycles, especially in controlling the depth distribution of upper-crustal seismicity. Fault Zones, Earthquakes, and the Seismogenic ZoneThe presence of long-lived, localized zones of shear deformation in the crust, or fault zones, implies that the fault rocks within are weaker than the surrounding country rocks and that their weakness is persistent [14,15]. The strength of the upper-crust is classically approximated using a Cou...

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Section: Nanocrystalline Principal Slip Zones Formed In Fault-slip Exmentioning

confidence: 96%

Section: Nanocrystalline Principal Slip Zones Formed In Fault-slip Exmentioning

confidence: 99%

Section: Nanocrystalline Principal Slip Zones Formed In Fault-slip Exmentioning

confidence: 99%

Section: Nanocrystalline Principal Slip Zones Formed In Fault-slip Exmentioning

confidence: 99%

Section: Formation Of Psz Nanostructures Amorphous Materials and Cpomentioning

confidence: 99%

See 3 more Smart Citations

Nanocrystalline Principal Slip Zones and Their Role in Controlling Crustal Fault Rheology

2019

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Crystal-plastic deformation of carbonate fault rocks through the seismic cycle

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Thermal weakening friction during seismic slip: experiments and models with heat sources and sinks

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show abstract

Coseismic ultramylonites: An investigation of nanoscale viscous flow and fault weakening during seismic slip

Cited by 40 publications

References 47 publications

Nanocrystalline Principal Slip Zones and Their Role in Controlling Crustal Fault Rheology

Nanocrystalline Principal Slip Zones and Their Role in Controlling Crustal Fault Rheology

Crystal-plastic deformation of carbonate fault rocks through the seismic cycle

Thermal weakening friction during seismic slip: experiments and models with heat sources and sinks

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