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Most Hazardous Segments of the Cascadia Rupture–Challenging the Worst-Case Scenario

Session: Earthquake Science, Hazards and Policy in Cascadia I

Type: Oral

Date: 4/20/2021

Presentation Time: 03:30 PM Pacific

Description: 

The lateral extent as well as the final size of potential future ruptures in Cascadia are poorly known. As a result, previous Cascadia tsunami studies are usually based on either “reasonable” or “worst-case” scenarios.

In this study, we calculate the tsunami hazard of M7-9 earthquakes using more realistic models that systematically vary both the geographic extent and slip of the rupture. To achieve this goal, we use rupture simulations derived from geodetic locking models to provide estimates of coseismic deformation at the ocean floor, and design rupture scenarios with variable hypocenters and rupture propagation. We then apply a non-linear algorithm to simulate full tsunami waveforms and generate tsunami amplitude profiles along the Cascadia coastline. By varying rupture dimensions and thus the seismic moment thresholds of these models, we find that while regional maximum coastal amplitudes are not unique for a given rupture size, increasing the rupture size beyond a magnitude of M_w≈8.5 will not significantly vary the tsunami hazard, especially in southern Cascadia, with the central segments playing the most crucial role. Numerical experiments attribute this property to the peculiar concave coastal morphology which also heightened hazard in central Cascadia (Oregon). Application of slip distribution from dynamic rupture scenarios in tsunami simulations also reveals that the possible coastal tsunami amplitude profiles in the US west coast from large Cascadia ruptures are largely insensitive to the choice of slip model. These results have significant implications in identifying the main sources of tsunami hazard along the US west coast, especially as a single worst-case rupture scenario does not uniquely correspond to the worst-case tsunami scenario at a given location.

Presenting Author: Amir Salaree

Student Presenter: No

Authors