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The Role of Transient Deformation in Interseismic Coupling in Cascadia

The Cascadia subduction zone is one of the most well studied regions for transient deformation. Slip reversals in Cascadia accompanied by non-volcanic tremor occur quasi-periodically depending upon the location along strike, and the slip tends to be concentrated at depths between 20-50 km along the subduction interface. The location of slow-slip, just downdip of the locked zone where great subduction earthquakes are generated, requires having a complete view of the interseismic cycle in order to fully characterize seismic hazards in the region. Fortunately, the Cascadia region has up to a three decade long record of daily deformation from geodetic-grade Global Navigation Satellite System (GNSS) stations that can be used to address the total transient slip budget in the region. In this study, I use daily position time series from over 270 GNSS stations between the Mendocino triple junction and northern Vancouver Island and determine the transient behavior at a number of scales on a station-by-station basis. I use a new detection algorithm that relies on the prominence of absement (absement is the integral of displacement and represents sustained motion over a time period). I classify transients based on different thresholds for absement prominence, and stack waveforms using 40 day windows around the transient detections. I then invert for slip using the three-component total transient displacement vectors, and compare the slip behavior from the different threshold values. I find that the slip models from lower threshold absement values have consistently more up-dip slip than the larger threshold absement values, indicating that the character of transient deformation shifts to smaller and more frequent events at shallower depths. From the transient slip models, I modulate the input interseismic velocities to account for the transient slip that is occurring and re-examine the coupling models in the region using a backflip approach. I examine the change in the downdip extent of strong coupling and finish by discussing implications for megathrust slip in the future.

Session: Constraining Seismic Hazard in the Cascadia Subduction Zone

Type: Oral

Room: 208A

Date: 4/20/2023

Presentation Time: 04:30 PM (local time)

Presenting Author: Brendan W. Crowell

Student Presenter: No

Additional Authors