CAREER: Impacts of Earthquake Shaking on Seafloor Sediment Stability and Landslide Hazards

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The massive amount of sediment moved by seafloor landslides is a hazard to coastal areas and to seafloor infrastructure including undersea cables. This project will use a combination of field observations from seismically active regions offshore Japan and offshore the Pacific Northwest along with geophysical data and sediment cores, and laboratory experiments that simulate the shaking induced by natural earthquakes to obtain a better understanding of why submarine landslides occur. The project uses newly acquired and legacy data from the International Ocean Discovery Program and the United States Geological Survey. Laboratory experiments will be performed on samples from each field site to understand the relationships between earthquake shaking, sediment physical properties, strength of the sediment, and the potential for a landslide. A key element of the education and outreach plan is to address under-representation of first-generation college students in STEM fields. This project will provide research experiences to first-generation college students majoring in the STEM field of earth sciences. A second major element of the education and outreach is a collaborative project with five other universities (Michigan, Penn State, Nebraska, Wisconsin, and Washington) to measure ‘fanquakes’, to provide outreach to hundreds of thousands of students and the public on the science of earthquakes by analogy to stadium shaking during sporting events. The project supports the training of graduate students. This project examines the relationship between earthquake shaking and stability of the uppermost 100 meters of ocean seafloor sediments, which is the critical zone where submarine landslides are most likely to occur. Earthquakes can trigger submarine landslides, and the massive sediment mobilized is a socio-economic hazard to populated coastal areas worldwide and seafloor infrastructure including undersea cables that route 99% of global internet data. The project goal is to understand the relative influence of earthquake shaking, sedimentation rate, and sediment lithology on overall slope stability. The hypotheses are 1) in hydrostatic pore pressure conditions, seafloor sediments exposed to earthquake shaking develop an enhanced shear strength greater than would be achieved without earthquake shaking, and 2) sedimentation rates high enough to develop overpressure will offset seismic strength gains because of the arrested consolidation. These hypotheses will be tested using a combination of field observations from three active margins sites with geophysical data and cores, controlled dynamic shaking laboratory experiments, and numerical simulations. The field sites span two primary types of active margins (convergent megathrust subduction zones (Cascadia and Japan Trench) and strike-slip (Queen Charlotte Fault Margin), and rely on both newly acquired and legacy data from the International Ocean Discovery Program and the United States Geological Survey. Controlled laboratory experiments will be performed using state-of-the-art dynamic shear experiments on samples from each field site to clarify relationships between seismic shaking, sediment physical properties, and shear strength response over a range of materials and shaking intensities. To understand more complex behavior in multiple dimensions within heterogeneous margin stratigraphy, numerical models will quantify depth limits (vertical effective stress) where sediments are no longer subjected to seismic strengthening, and how seismic strengthening varies between different active margins with differing lithologies, sedimentation rates, and earthquake histories.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.