NSF funding info: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2003489&HistoricalAwards=false
This is a new project with funding from the National Science Foundation's Marine Geology and Geophysics program, in collaborating with Dr. Mark Zumberge at the Scripps Institution of Oceanography, UC San Diego. The goal is to search for shallow slow slip in Cascadia (Figure 1). We are scheduled to deploy a new type of seafloor scientific instrument, a seafloor optical fiber strainmeter (Figure 2), off the coast of Oregon in summer 2021 for a period of 2 years.
The Cascadia Subduction zone off the west coast of Northern California, Oregon, Washington, and British Columbia is where the Juan de Fuca tectonic plate collides with, and sinks below, the North American tectonic plate. Subduction zones host the largest earthquakes in the world, and the Cascadia subduction zone in particular experienced an earthquake with an estimated magnitude of 9.0 earthquake on January 26, 1700. The expected recurrence interval for large earthquakes in this region is 300-500 years.
In between large earthquakes, the Cascadia subduction zone is not dormant. Rather, it's home to two recently discovered phenomena: slow slip events and tectonic tremor. In a slow slip event, the deeper extent of the interface between the two tectonic plates slips, as in an earthquake, but does so more slowly. While earthquake slip occurs over the course of seconds, slow slip occurs over the course of days to weeks. A recent study by Prof. Bartlow (Bartlow, 2020, read more about it here) found a possible second, shallower slow slip zone offshore (Figure 3A below).
The goal of this upcoming study is to attempt to detect this shallow slow slip zone. If we confirm the presence of shallow slow slip it will have important implications for forecasting earthquake hazards in Casacadia, as slow slip in this area is expected to add stress to the locked zone and potentially trigger a large earthquake in the future.
Figure 1. Map showing the Cascadia subduction zone. The Gorda and Explorer “plates” are part of the larger Juan de Fuca tectonic plate, but move in slightly different directions and can be considered sub-plates.
Figure 2. Diagram of a seafloor optical fiber strainmeter, from Zumberge et al., 2018
Figure 3. A) Time-averaged slow slip rate (colors) and contours of density of tremor detections (brown lines) on the Cascadia plate interface (modified from Bartlow, 2020). B) Same as A, but with a comparison to the location of the locked zone (red and yellow colors) from Schmalzle et al. (2014).