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The Role of Transient Deformation in Interseismic Coupling in Cascadia

Description: 

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

Date: 4/20/2023

Presentation Time: 04:30 PM (local time)

Presenting Author: Brendan W. Crowell

Student Presenter: No

Invited Presentation: 

Authors