20-26. Geotechnical and geomorphic investigations of submarine slope stability and seascape evolution in the Cascadia Subduction Zone

CLOSED

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Submarine landslides can damage submarine infrastructure, trigger or contribute to damaging tsunamis, mobilize large volumes of sediment, and may provide an independent source of earthquake recurrence information along subduction zone margins. In the Cascadia Subduction Zone (CSZ) and other subduction zones globally, shaking-triggered sediment gravity flows that leave behind deep sea turbidite records are a critical component of long-term earthquake recurrence estimates along the margin and are used to infer greater earthquake frequency in southern Cascadia. However, the sources, triggering mechanisms, and pathways of these turbidity flows are poorly constrained, and lead to substantial uncertainty in the inferred earthquake recurrence and seismic hazard of the CSZ. Furthermore, the timing, distribution, and evolution of large submarine landslides along Subduction Zones has been under-explored, and may provide constraints on past shaking intensities, earthquake frequency, and the spatial extent of shaking, as well as seafloor and subsurface conditions associated with subduction zone tectonics.

Ongoing USGS and academic initiatives to compile margin-wide datasets, including high-resolution multibeam bathymetry data, onshore-offshore crustal scale geophysical data, sediment cores, and submarine landslide mapping, as well as observed and simulated ground motions, provide a rich foundation for new geological and geotechnical analyses of the underlying processes that drive submarine landslide initiation, seafloor geomorphology, sediment transport and deposition, and event dating.

We encourage innovative research proposals designed to advance our understanding of submarine landslides in the Cascadia Subduction Zone that can be connected to subduction zone processes, including preconditioning factors, sensitivity to triggering, or associating geomorphic signatures to paleoshaking. Integration and synthesis of models and datasets, including data from other subduction zones, along with novel approaches to addressing the complex interrelationships among these research areas are encouraged.

Possible research themes include, but are not limited to:

Characterization of the role of ground shaking and or pore pressure on the initiation of submarine landslides

Understanding the relationships between earthquake ground motion amplitude, duration, and frequency content, with landslide failure style and size, is a fundamental component of investigations into the role of earthquake shaking in remobilizing and redistributing sediment across marine environments. The role of cyclic softening and liquefaction on the initiation of submarine landslides may be investigated by developing or adapting physical, numerical, or theoretical models of submarine slope failure or other related shaking-triggered failure phenomena (e.g., as for subaerial landslides, dynamic earthquake triggering, or liquefaction). Improvements to our understanding of submarine landslide triggering in response to long-duration subduction zone earthquake shaking, particularly those instabilities leading to submarine turbidite or landslide deposits, may better constrain the magnitude, timing, and shaking intensity of past CSZ earthquakes and improve our assessments of submarine landslide related hazard and risk.

The influence of sediment properties and stratigraphic patterns (e.g., lithology, grain size, slope morphology, presence of weak layers) on preconditioning slopes for failure

Determining which types of sedimentary environments are prone to generating mass failures and downslope transport during large (M>7) earthquakes is critical to hazard assessments. For example, spatially continuous, parallel bedded strata can allow lateral migration and vertical confinement of pore fluid leading to generation of super-hydrostatic ambient pore fluid pressures (overpressure) that can reduce shear strength and promote failure along bedding planes. Research proposals are welcomed that consider one or more preconditioning factors to explain the observed distribution of landslide type, size, and frequency along the CSZ margin.

Application of terrestrial geomorphologic techniques to seascapes

Understanding the spatial-temporal distribution of submarine landslides, independent of existing turbidite and coastal subsidence records, could provide additional constraint on CSZ earthquake recurrence, and possible north-south variation in earthquake recurrence and magnitude. We encourage projects seeking to develop, or apply, model(s) relating physical submarine processes of deposition and erosion to morphometric expression in the seascape to predict submarine landslide ages. For example, can measured submarine landslide roughness be used to estimate deposit age based on known ages and roughness of other slides or to calibrate a seascape evolution model.

Alternative research themes within the scope of improving our knowledge of the Cascadia Subduction Zone via submarine landslides are also welcome. Interested applicants are strongly encouraged to contact the Research Advisors early in the application process to discuss project ideas.

Proposed Duty Station: Seattle, Washington; Santa Cruz, California; or Moffett Field, California

Areas of PhD: Geotechnical engineering, geology, geophysics, seismology, or related fields (candidates holding a Ph.D. in other disciplines, but with extensive knowledge and skills relevant to the Research Opportunity may be considered).

Qualifications: Applicants must meet the qualifications for one of the following: Research Engineer, Research Geologist, Research Geophysicist.

(This type of research is performed by those who have backgrounds for the occupations stated above.  However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Human Resources Office Contact: Paj Shua Cha, 650-439-2455, pcha@usgs.gov