Searching for Empirical Links Between Shaking and Turbidity Current Generation in the Cascadia Subduction Zone
Description:
Seismic hazard estimates for the Cascadia Subduction Zone (CSZ) rely on geologic observations such as magnitude and recurrence intervals derived from offshore turbidites. These assume that shaking from CSZ earthquakes remobilizes seafloor sediment, but empirical observations of seismically-generated turbidity currents are lacking in the CSZ. Few quantitative estimates exist linking shaking intensity to turbidity current generation, challenging our ability to fully constrain past shaking and earthquake characteristics. The Ocean Networks Canada (ONC) cabled seafloor array in Barkley Canyon provides concurrent seismic, turbidity, and other oceanographic data in a seismically active portion of the margin. Multiple large regional (>M6) and moderate local (<M6) earthquakes occurred during the ONC operating period 2016-present, allowing us to search for direct observations of shaking and concurrent canyon system processes.
We seek empirical observations of seismically-generated turbidity currents to determine if a threshold level of shaking is associated with turbidity currents. Using the Barkley Canyon (BACAX) oceanographic 2019 sensor data, we create a catalog of turbidity events at BACAX. We do so with a short-term average/long-term average (STA/LTA) algorithm to identify elevated levels of turbidity and require a subsequent exponential decay. We compare our catalog to characteristic oceanographic measurements (i.e., oxygen, temperature), and examine water velocities for each event. The combination of data suggests that all 17 events at BACAX are internal tide generated, and unrelated to shaking. We also present results for a chronologically expanded catalog, subsequently comparing any events that are unexplained by non-seismogenic triggers to measurements of shaking, to identify if there is a statistically significant link between ground motions and turbidity events. This method may be used at other sites where existing data may reveal such relationships.
Session: Constraining Seismic Hazard in the Cascadia Subduction Zone
Type: Oral
Date: 4/20/2023
Presentation Time: 02:45 PM (local time)
Presenting Author: Valerie J. Sahakian
Student Presenter: No
Invited Presentation:
Authors
Valerie Sahakian Presenting Author Corresponding Author vjs@uoregon.edu University of Oregon |
Debi Kilb dkilb@ucsd.edu University of California, San Diego |
Marcus Chaknova marcus.chaknova@gmail.com University of Oregon |
Fabio Cabrera De Leo fdeleo@uvic.ca Ocean Networks Canada |
Andrea Ogston ogston@uw.edu University of Washington |
Jenna Hill jhill@usgs.gov U.S. Geological Survey |
Maureen Walczak mo.walczak@oregonstate.edu Oregon State University |
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Searching for Empirical Links Between Shaking and Turbidity Current Generation in the Cascadia Subduction Zone
Category
Constraining Seismic Hazard in the Cascadia Subduction Zone