Fracture energy of Cascadia input sediments integrated into a global compilation
Abstract
The mechanical properties of sediments at subduction zones are important for understanding rupture propagation through the accretionary prism during megathrust earthquakes. Incoming sediments on the subducting plate often contain abundant clay minerals, which significantly influence the overall frictional behavior of fault gouges. However, the clay content varies for subduction margins globally. At Cascadia, where the incoming Juan de Fuca plate is small, the sediments are relatively clay-poor. To establish the frictional properties of the shallow Cascadia subduction zone and place the results in a global context, we conducted a series of high velocity rotary shear experiments on core samples retrieved from input sediments as well as individual clay species. Experiments focused on the effects of lithology and normal stress on the coseismic frictional behavior and fracture energy of the materials. Comparing our results to an extensive compilation of high velocity experiments conducted on phyllosilicate gouges and other common subduction input materials, we identified three trends with increasing normal stress: 1) peak stress during acceleration scales linearly, 2) the thermal weakening distance, which characterizes the amount of slip over which the majority of thermal weakening takes place, decreases exponentially, and 3) the fracture energy shows no systematic trend. However, fracture energy varies with lithology. Clay-rich gouges under wet conditions have the lowest fracture energy, but fracture energy for both dry and wet clay-rich gouges can be several orders of magnitude lower than estimates from intact rocks. Overall, clay-rich lithologies promote rupture propagation through shallow subduction zone faults and minimize spatial variations in frictional behavior, allowing earthquakes to propagate to the trench. However, our results suggest Cascadia input sediments have relatively high fracture energy, which may inhibit shallow earthquake slip.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR23E0158S
- Keywords:
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- 3902 Creep and deformation;
- MINERAL PHYSICS;
- 8010 Fractures and faults;
- STRUCTURAL GEOLOGY;
- 8034 Rheology and friction of fault zones;
- STRUCTURAL GEOLOGY;
- 8045 Role of fluids;
- STRUCTURAL GEOLOGY