 |
| Titel |
Experimental Measurements of Fault Wear and Permeability Evolution along Faults during Progressive Slip |
| VerfasserIn |
Marc Andre Strutz, Tom Mitchell, Jörg Renner |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250056346
|
|
|
|
|
|
| Zusammenfassung |
| Little is currently known about the dynamic changes in fault-parallel permeability along
rough faults during progressive slip. With increasing slip, asperities are worn to produce
gouge which can dramatically reduce along fault permeability within the slip zone. However,
faults can have a range of roughness which can affect both the porosity and both the amount
and distribution of fault wear material produced in the slipping zone during the early stages of
fault evolution.
In this novel study we investigate experimentally the evolution of permeability along a
fault plane in granite sawcut sliding blocks with a variety of intial roughnesses in a triaxial
apparatus. Drillholes in the samples allow the permeability to be measured along the fault
plane during loading and subsequent fault displacement. Use of the pore pressure
oscillation technique (PPO) allows the continuous measurement of permeability
without having to stop loading. To achieve a range of intial starting roughnesses,
sawcut surfaces were prepared using a variety of corundum powders ranging from 10
μm to 220 μm, and for coarser roughness were air-blasted with glass beads up to
800 μm in size. Fault roughness has been quantified with a laser profileometer.
During sliding, we measure the acoustic emissions in order to detect grain cracking
and asperity shearing which may relate to both the mechanical and permeability
data.
Permeability shows relative reductions of up to over 4 orders of magnitude (from 10-14
m2 down to as low as 10-18 m2) during stable sliding as asperities are sheared to produce a
fine fault gouge over displacements of up to 6 mm. This variation in permeability is
greatest for the roughest faults, reducing as fault roughness decreases. The onset
of permeability reduction is contemporaneous with a dramatic reduction in the
amount of detected acoustic emissions, where a continuous layer of fault gouge has
developed and asperities of the host rock are no longer in contact. Following large
stress drops and stick slip events, permeability can both increase and decrease due
to dynamic changes in pore pressure during fast sliding events. The amount of
fault gouge produced is related to the initial roughness, with the roughest faults
showing thicker fault gouge layers at the end of slip. We quantify the roughness
both before and after experiments in addition to measuring the amount of wear
material produced. We also explore the effect of strain rate on wear material produced.
Our results have significant implications for permeability evolution of natural fault
zones in which many existing studies have been shown to have a wide range of
roughnesses. |
|
|
|
|
|
|