Lydia M. Staisch
Synthesizing geological and geophysical datasets to address great megathrust earthquake recurrence, rupture, and radiation along the Cascadia Subduction Zone
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Subduction zone earthquakes are among the most impactful natural hazards that occur on Earth. The Cascadia Subduction Zone (CSZ) of the US Pacific Northwest and coastal British Columbia has experienced in prehistory numerous great megathrust earthquakes (M>8.0). Future earthquakes are inevitable and their impacts could cripple the region (Schulz, 2015). Despite substantial knowledge gained from decades of geoscience research, estimates of the sizes and frequencies of Cascadia earthquakes remain uncertain.
Earthquake-cycle models are commonly invoked along subduction zones, and earthquakes repeat with some degree of regularity from tectonic loading and release. However, estimated recurrence intervals of past Cascadia megathrust earthquakes vary substantially, and statistical and computer models suggest event clustering behavior.
Much of our current understanding of Cascadia earthquake hazards comes from evidence found in onshore and marine geologic records and from modern recurrence in other subduction zones. Differences between geologic records might be related to their sensitivity as earthquake recorders (i.e., “evidence thresholds”). For example, the occurrence and preservation of coseismic coastal subsidence depends on several parameters including rupture extent, slip distribution, and inter-event coastal uplift. Similarly, offshore turbidite records depend on the frequency and extent of ground motion shaking during past Cascadia earthquakes, as well as on sediment availability.
The USGS Powell Center Cascadia Earthquake Hazards Working Group was formed to synthesize geological and geophysical information relevant to CSZ megathrust earthquakes. Participants include a diverse range of researchers, from early career to emeritus, who are experts in tectonics, geophysics, crustal structures, landslides, sedimentology, paleoseismology, land-level changes, geodesy, mantle and crustal rheology, and earthquake rupture dynamics. Throughout our first week-long meeting in March 2019 we also engaged risk-communication experts to ensure that our discoveries and uncertainties are translated most effectively to communities and other stakeholders.