A Sensitivity Analysis of Seafloor Pressure Sensors for the Detection of Offshore Slow Slip Earthquakes in the Cascadia Subduction Zone
Date: 4/25/2019
Time: 06:00 PM
Room: Grand Ballroom
Seafloor pressure measurements have been used to detect slow slip earthquakes (SSEs) in the updip portions of several subduction zones, typically by differencing pressure records to eliminate oceanographic signals assumed to be regionally correlated. We evaluate this assumption and explore how to optimize sensor geometry to minimize oceanographic noise and detect SSEs. Our analysis focuses on the Cascadia Subduction Zone, where bottom pressure data were collected as part of the 2011-2015 Cascadia Initiative seismic experiment, but where sensor geometry was not optimized for SSE detection. We find oceanographic bottom pressure to be strongly depth dependent with tidally filtered, detrended RMS amplitudes of >6 cm of water on the continental shelf and <2 cm on the abyssal plane. This compares to an observed 1-6 cm peak vertical displacement from offshore SSEs in other settings. Differencing pressure records can yield <1 cm RMS when depths are matched, at separations <100 km on the shelf and slope and as large as 300 km on the plane. We directly compare these data to hindcast seafloor pressure from regional oceanographic circulation models and find that differencing results are consistent between observation and model. We also calculate seafloor displacements from a half-space fault model for a range of SSE scenarios, merging these with hindcast pressure time series to simulate observational records. These synthetics show that constant-depth sensor lines can reliably detect deformation at least as low as 1.5 cm. We find that a Mw 6.3 SSE, such as detected elsewhere, would require a decadal scale observational effort to reliably detect given the local convergence rate and likely recurrence intervals. Our results suggest that future experiments should deploy sensors along lines of constant depth to maximize detectability. However, this approach needs to be evaluated in observed and hindcast pressure records from other subduction zones to determine whether it is widely applicable, as circulation patterns vary between regions.
Presenting Author: Erik K. Fredrickson
Authors
Erik K Fredrickson erikfred@uw.edu University of Washington, Seattle, Washington, United States Presenting Author
Corresponding Author
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William S D Wilcock wilcock@uw.edu University of Washington, Seattle, Washington, United States |
David A Schmidt dasc@uw.edu University of Washington, Seattle, Washington, United States |
Parker MacCready pmacc@uw.edu University of Washington, Seattle, Washington, United States |
Emily Roland eroland@uw.edu University of Washington, Seattle, Washington, United States |
Mark A Zumberge mzumberge@ucsd.edu Scripps Institution of Oceanography, San Diego, California, United States |
Glenn Sasagawa gsasagawa@ucsd.edu Scripps Institution of Oceanography, San Diego, California, United States |
Alexander L Kurapov alexander.kurapov@noaa.gov Oregon State University, Corvallis, Oregon, United States |
A Sensitivity Analysis of Seafloor Pressure Sensors for the Detection of Offshore Slow Slip Earthquakes in the Cascadia Subduction Zone
Category
Advances in Tectonic Geodesy