What processes cause and regulate the interplay between ductile flow in the deep crust and frictional processes in the seismogenic zone?

Subduction zones-regions of Earth's crust where one tectonic plate dives beneath another-are usually but not always associated with frequent, violent earthquakes. Occasionally, the downgoing plate slides slowly, smoothly, and almost silently under the overriding plate. Canadian scientists have contributed significantly to the research of seismic slow slip phenomena with geophysical observations of the Cascadia subduction zone. However, field observations, rock experiments, and theoretical developments are also needed to advance our understanding of these newly identified earthquake phenomena. The proposed research project, with implications for future earthquakes offshore western Canada, aims to expand our knowledge of mechanical processes that link mega earthquakes in the upper crust to steady and continuous slip in the lower crust via the brittle-ductile transition zone, which hosts the seismic slow signals. The importance of this research lies in the potential relationship between the fault transition zone and the parts of faults that generate destructive earthquakes. Some calculations find that the probability of a large earthquake occurring during a slow slip event is 30-100 times greater than background probabilities. A better understanding of the various slow earthquake types may deepen our knowledge of the tectonic framework required for the formation of subduction systems, including the rupture style of large megathrust earthquakes. Quantifying fault slip rates in active tectonic environments over human timescales is critical to assessing seismic risk to human life and property. Project goals will involve Canadian and international collaborators and train one graduate student to become knowledgeable and proficient in science communication, and earthquake research, collaborate with world-leading research groups, and gain access to world-class infrastructure currently unavailable in Canada. The project will be performed at the ETH (Federal Institute of Technology) in Zurich, Switzerland. Canada will benefit from the research by furthering our understanding of processes generating many of the planet's geohazards, which can feed into policy developments regarding geohazard and environmental protection.