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Tectonic Oversteepening, Sediment Accretion, and Lower Slope Failure in the Cascadia Subduction Zone – A Recipe for Abyssal Seismoturbidites and Insights Into Earthquake History

Description: 

Seismic strengthening and related processes are often cited to explain the dearth of large submarine landslides on active margins; however, recent examination of seafloor bathymetry has revealed extensive mass wasting of the continental slope along the Cascadia Subduction Zone. Hill et al. (2022) suggested these failures may be the primary source of abyssal seismoturbidites that comprise the longest earthquake records in the region. Deriving robust earthquake recurrence estimates from these records though, requires rigorous investigation of the processes of slope development and failure preconditioning. From 2019-2023, the USGS and MBARI conducted extensive geophysical surveys and geologic sampling along the Cascadia margin, including >6700 km of Sparker MCS and Chirp subbottom data, 470 sediment cores (380 <2m ROV-based vibracores, 90 6-8m piston cores), along with AUV 1-m bathymetry and subbottom data. These data offer an unprecedented look at the structure and morphology of the deformation front and provide insight to the mechanics of earthquake triggered slope failure. Northern Cascadia is characterized by steeply dipping, asymmetric, landward vergent thrust folds with steeper seaward limbs prone to translational block slides along bedding planes. In central Cascadia, low angle, imbricate thrust faults have created a stepped terrace morphology with steep ledges. Failures occur at the forelimb of the fold, exposing truncated strata at the seafloor. In southern Cascadia, steeply dipping thrust faults create lower relief folds, yet failures occur on the 4-6° seaward face of the frontal thrusts. Two factors appear key in preconditioning the slopes for failure: (1) the dynamic uplift and permanent deformation creates oversteepening; (2) accretion of abyssal plain sediment into the outer wedge provides unlimited recharge of relatively weak and unstable material. These two processes appear to be keeping pace with earthquake triggering and outweigh the effects of compaction induced strengthening.

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