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Marine Seismoturbidites in the Cascadia Subduction Zone: Filling the Gaps and Refining the Offshore Records of Earthquake Shaking

Description: 

The Cascadia Subduction Zone has a well-developed marine paleoseismic record, yet uncertainties in age and correlation among deposits over long distances, as well as questions about triggering mechanisms make it difficult to distinguish the length and magnitude of shaking in past events. Hill et al. (2022) proposed that pervasive mass wasting of the lower slope in Cascadia is a primary source of abyssal seismoturbidites that would avoid many of the pitfalls and arguments commonly made against turbidite stratigraphy and allow for new sampling locations that fill critical spatial gaps in the existing records. To test this hypothesis, we collected 8-9m piston cores from 20 new sites in central and northern Cascadia, on the abyssal plain proximal to the deformation front and from isolated lower slope basins. Several of these sites are complemented by detailed AUV bathymetry and subbottom data, along with transects of closely spaced, ROV-based <2m vibracores. Our preliminary age dating shows these new sites contain a robust record of Holocene abyssal turbidites that are most likely derived from strong earthquake shaking. Initial radiocarbon dating and age models from several of our sites suggest chronologic correlation of the seismoturbidites along large stretches of the margin. There are distinct differences in deposit characteristics (e.g., range of grain sizes or number of pulses) that vary over both time and space, and likely reflect the inputs of multiple slope failure sources during a given event. The type and degree of earthquake triggered slope failure is variable along the margin, such that some locations may contain extra and/or missing events, highlighting the need for detailed chronology. The spatial density of these new sites combined with the existing records offers a valuable opportunity to assess variability in earthquake rupture patterns along the Cascadia margin and provide insight into extent of slope failure along the margin. Our results also suggest similar seismoturbidite records may be found outside of submarine canyon systems on other subduction margins with a similar steep slope morphology.

Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Jenna

Student Presenter: No

Invited Presentation: 

Authors