Hazard Constraints on Potentially Tsunamigenic Submarine Crustal Faults in the Northern Cascadia Forearc

Session: Understanding Non-Traditional Seismic Tsunami Hazards
Type: Oral
Date: 4/28/2020
Time: 04:45 PM
Room: 120 + 130
Description: 

Probabilistic tsunami hazard assessment of seismic sources requires constraints on earthquake rupture area, rupture style and frequency, as well as high-resolution bathymetry and topography to enable accurate tsunami modelling. For the Cascadia subduction zone megathrust, source characteristics are relatively well constrained by multiple datasets, although uncertainties remain, e.g., regarding the potential involvement of splay faults and event recurrence is approximated from on- and offshore paleoseismic data. Modelling and paleo-event data show that the outer coastlines and inlets from northern California to British Columbia receive significant tsunami waves from megathrust events. Within the Juan de Fuca and Georgia Straits between Vancouver Island and mainland North America, smaller waves can be expected from megathrust sources. However, this area of the Cascadia forearc hosts a number of other potential tsunami sources in the form of submarine crustal faults that accommodate dominantly right-lateral transpression on the northern limb of the Olympic orocline. Many of these faults have only recently been identified as Holocene-active, and their tsunami hazard has yet to be assessed. Although crustal earthquake magnitudes and frequencies are much lower than megathrust sources, tsunami wave heights may be significant and warning times short between the arrival of seismic and tsunami waves. We focus on improving hazard constraints on several of these faults, including the Skipjack Island, Birch Bay and Devil’s Mountain faults. Challenges include a general lack of significant historical activity and of paleoseismic and paleotsunami data, poorly constrained sub-seafloor structure, the potential for complex ruptures on multiple fault strands and for tsunamigenic contributions from coseismic landslides. Such challenges will likely preclude accurate probabilistic hazard assessment, but a number of scenarios can be constrained and modelled.

Presenting Author: Lucinda J. Leonard

Authors