Models describing the slip dynamics of a fault assume generally an isotropic interface giving rise to shear forces which are parallel to the slip direction. However, structured surfaces may be associated with an anisotropic frictional behavior, which is characterized by a dependence of the magnitude of friction force on slip direction and the presence of friction force components transverse to the slip direction. The arrangement of atoms in the crystal structure of the minerals composing the rock slab, the foliation and lineations originating from the rock deformation, and the presence of gouges formed as a consequence of rock erosion, contribute to the structuring of the surface on different length scales. Among these aspects, only the former is related to intrinsic properties of the fault, and its influence on the frictional properties is therefore independent on the rock history. In order to study the relation between frictional properties and crystal structure, we performed a nanotribological characterization of the surface of prominent mineral species with a scanning force microscope, where a micrometric tip mounted on an elastic cantilever is scanned by piezoelectric actuation along all directions of the sample surface on a nanoscopic area, while vertical deflection and lateral torsion of the cantilever are monitored in real-time, allowing for the quantitative determination of the friction force vectors. Antigorite, the high-temperature, high pressure polymorph of serpentine, is a mineral with a prominent role in defining the mechanical behavior of faulted regions. Indeed, there is general consensus that it forms in the forearc mantle wedge by hydration of olivine and pyroxenes through aqueous fluids released in the downgoing slab, upon increasing pressure and temperature. We asses frictional anisotropies as high as 100% of individual crystal domains of antigorite [1]. This anisotropy is related to the peculiar wavy arrangement of the TO-layer and the presence of reversals occurring along the a-axis of the tetrahedral sheets of antigorite. If we associate the known strain-induced lattice preferred orientation (LPO) of serpentine rocks to our nanoscopic observation, a strong anisotropic frictional behavior of sliding surfaces of serpentinized rocks in subduction zones can be inferred. The results obtained with other phyllosilicates such as mica muscovite and phlogopite will be also presented for comparison. Impressive phenomena can be envisaged if frictional anisotropy is introduced in the dynamical description of faults such as mechanical instabilities giving rise to a strong declination of the slip vector with respect to the plate convergence direction, explaining seismic degree of partitioning otherwise to be considered anomalous. On the other hand, for specific LPO mechanisms, a strain softening behavior of the serpentinized mantle wedge can be inferred, providing a physical explanation to its postulated aseismic character. [1] Campione M., and Capitani G. C., Subduction-zone earthquake complexity related to frictional anisotropy in antigorite, Nature Geoscience, in press, 2013.

Campione, M., Capitani, G. (2013). The Impact of Frictional Anisotropy of Serpentine on Thrust Fault Slip at Subduction Zones. In Proceedings.

The Impact of Frictional Anisotropy of Serpentine on Thrust Fault Slip at Subduction Zones

CAMPIONE, MARCELLO;CAPITANI, GIANCARLO
2013

Abstract

Models describing the slip dynamics of a fault assume generally an isotropic interface giving rise to shear forces which are parallel to the slip direction. However, structured surfaces may be associated with an anisotropic frictional behavior, which is characterized by a dependence of the magnitude of friction force on slip direction and the presence of friction force components transverse to the slip direction. The arrangement of atoms in the crystal structure of the minerals composing the rock slab, the foliation and lineations originating from the rock deformation, and the presence of gouges formed as a consequence of rock erosion, contribute to the structuring of the surface on different length scales. Among these aspects, only the former is related to intrinsic properties of the fault, and its influence on the frictional properties is therefore independent on the rock history. In order to study the relation between frictional properties and crystal structure, we performed a nanotribological characterization of the surface of prominent mineral species with a scanning force microscope, where a micrometric tip mounted on an elastic cantilever is scanned by piezoelectric actuation along all directions of the sample surface on a nanoscopic area, while vertical deflection and lateral torsion of the cantilever are monitored in real-time, allowing for the quantitative determination of the friction force vectors. Antigorite, the high-temperature, high pressure polymorph of serpentine, is a mineral with a prominent role in defining the mechanical behavior of faulted regions. Indeed, there is general consensus that it forms in the forearc mantle wedge by hydration of olivine and pyroxenes through aqueous fluids released in the downgoing slab, upon increasing pressure and temperature. We asses frictional anisotropies as high as 100% of individual crystal domains of antigorite [1]. This anisotropy is related to the peculiar wavy arrangement of the TO-layer and the presence of reversals occurring along the a-axis of the tetrahedral sheets of antigorite. If we associate the known strain-induced lattice preferred orientation (LPO) of serpentine rocks to our nanoscopic observation, a strong anisotropic frictional behavior of sliding surfaces of serpentinized rocks in subduction zones can be inferred. The results obtained with other phyllosilicates such as mica muscovite and phlogopite will be also presented for comparison. Impressive phenomena can be envisaged if frictional anisotropy is introduced in the dynamical description of faults such as mechanical instabilities giving rise to a strong declination of the slip vector with respect to the plate convergence direction, explaining seismic degree of partitioning otherwise to be considered anomalous. On the other hand, for specific LPO mechanisms, a strain softening behavior of the serpentinized mantle wedge can be inferred, providing a physical explanation to its postulated aseismic character. [1] Campione M., and Capitani G. C., Subduction-zone earthquake complexity related to frictional anisotropy in antigorite, Nature Geoscience, in press, 2013.
abstract + poster
Subduction zones, Serpentinites, Antigorite, Frictional anisotropy, Nanotribology, Earthquakes
English
American Geophysical Union Fall Meeting
2013
Proceedings
2013
none
Campione, M., Capitani, G. (2013). The Impact of Frictional Anisotropy of Serpentine on Thrust Fault Slip at Subduction Zones. In Proceedings.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/68772
Citazioni
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
Social impact