Earthquake Rupture Driven by Shear Localisation within the Fault Gouge
Abstract
Regions of highly localised shear within the gouge of earthquake fault zones have been reported in several field observations. The emergence of shear localisation can be related to the thermal pressurisation of pore fluid during the rapid shearing of the gouge. In their seminal work, Platt et al. [2014] studied how the localisation width depends on the hydro-thermal properties of the gouge and highlighted that a dramatic reduction of the frictional strength can result from shear localisation within the gouge. The latter is thereby expected to have a significant impact on the earthquake rupture whose propagation is driven by the dynamic weakening of the fault frictional strength. Here, we investigate the interplay between shear localisation and earthquake dynamics. We rely on a boundary integral formulation of the elastodynamic relations expressed at the surfaces of two semi-infinite solids. The frictional constitutive behaviour at each location of the interface emerges from the thermo-poro-mechanical response of the layer of a fluid-saturated gouge computed using the model derived by Platt et al. [2014]. This coupled system is used to simulate the dynamic propagation of earthquake ruptures and enables a direct visualisation of the localisation-delocalisation sequences arising in the wake of the rupture fronts. The post-seismic distribution of the shear strain along the fault plane is then mapped for different types of gouge properties. We discuss how the latter affect the rupture dynamics by selecting the thickness of the shear localisation. We notably present how more violent ruptures are associated with highly localised regions that produce an abrupt loss of frictional strength. Overall, this work sheds a new light on the interplay between earthquake ruptures and the mechanical behavior of fault gouge and opens up new perspectives to connect the shear localisation observed on the field to the dynamics of the seismic events that produced it.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR41A..02B
- Keywords:
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- 1207 Transient deformation;
- GEODESY AND GRAVITY;
- 3902 Creep and deformation;
- MINERAL PHYSICS;
- 4317 Precursors;
- NATURAL HAZARDS;
- 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS