Deep Coseismic Slip in the Cascadia Megathrust can be Consistent with Coastal Subsidence

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Diego Melgar , Valerie Sahakian, Amanda Thomas


At subduction zones, the down-dip limit of slip represents how deep an earthquake can rupture. For hazards it is important - it controls the intensity of shaking and the pattern of coseismic uplift and subsidence. In the Cascadia Subduction Zone, because no large magnitude events have been observed in instrumental times, the limit is inferred from geological estimates of coastal subsidence during previous earthquakes; it is typically assumed to coincide approximately with the coastline. This is at odds with geodetic coupling models, it leaves residual slip deficits unaccommodated on a large swath of the megathrust. Here we will show that ruptures can penetrate deeper into the megathrust and still produce coastal subsidence provided slip decreases with depth. We will discuss the impacts of this on expected shaking intensities



Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics


cascadia, paleoseismology, rupture modeling


Published: 2021-12-08 13:41

Last Updated: 2021-12-08 13:41


CC BY Attribution 4.0 International

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Conflict of interest statement:

Data Availability (Reason not available):
The kinematic ruptures were generated using the FakeQuakes code which is part of the MudPy source modeling toolkit available on GitHub (, the latest version is archived ione Zenodo at Melgar (2021). The rupture models and their coastal subsidence estimates are archived on Zenodo at (Melgar et al., 2021). The ground motions were calculated using the OpenQuake Engine framework (Pagani et al., 2014,

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