The Role of Fluids in Controlling Giant Subduction Zone Earthquakes

Professor Pascal Audet leaning against a pillar at the entrance of the new Science, Technology, Engineering and Mathematics (STEM) building. In the background, the line of pillars continues.

Professor Pascal Audet with Banting Fellow Andrew Schaeffer

Department of Earth and Environmental Sciences

The west coast of North America may one day be forever indebted to Professor Pascal Audet and Banting Fellow Andrew Schaefer for laying the groundwork to map the area of highest risk from an impending giant earthquake and resulting tsunami.

The Earth is made up of seven major and several minor tectonic plates that are constantly shifting at the Earth surface. Regions where one tectonic plate slides underneath another one are known as subduction zones. As Audet states, these zones “represent the highest seismic hazard on the planet due to the level of ground shaking and the potential for tsunami waves during giant earthquakes.” One major zone, known as the Cascadia subduction zone, is located along the west coast of North America and is renowned for experiencing giant earthquakes. It is here that Audet and Schaefer conducted most of their research. In the first study to ever use a combination of instruments located on land and on the sea floor, they were able to combine these data sets and characterize the transition from high to low friction between the tectonic plates. These methods use technology that stems from ultrasonography — an imaging technique using soundwaves to view an internal structure. With this technology, they can create images of the subduction zone that allow them to see depths beyond ~15 km to 20 km. At a distance this far below the surface, there are fluids released from the subducting plate, which is the one being forced under the upper plate, that consequently lower the friction between the plates and limit its extension towards the offshore of North America.

Thanks to this innovative discovery, other researchers are improving their predictions of the level of ground shaking and infrastructure damage that future large earthquakes in Cascadia will cause. Predictions of this sort are extremely useful for urban centres that could be affected by large earthquakes, for example, Vancouver, Victoria, Seattle and Portland. Furthermore, this discovery has prompted future plans for the installation of more seismic stations on the Pacific Ocean floor in order to record the variation in friction along the length of the Cascadia subduction zone.

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Fluid pressure and shear zone development over the locked to slow slip region in Cascadia

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