The Role of Slope Failures in Geohazards and Continental Margin Morphology

Derek Sawyer, Ohio State University
Event Location: 
Event Date: 
Thursday, April 2, 2015 - 3:00pm
Event Type: 
SCMSS Seminar Series


Continental margins are pervasively re-shaped by processes associated with slope failures (submarine landslides), which are among the largest sedimentary events on Earth. Engineering factor-of-safety techniques can quantify the limits of stability for a given system. However, immediately after shear failure begins, a broad spectrum of post-failure types are possible from slow-moving slump-type failures, to rapidly accelerating and disintegrating fluidized debris flows that can run 100s of kilometers away from the source. The post-failure mobility of submarine slope failures controls the size of a tsunami and scale of impact forces, ability to scour the seafloor, and the ultimate characteristics of the resultant deposit. Here, 3-D seismic reflection data, core and log data from Integrated Ocean Drilling Program Expedition 308 (Ursa Basin, Gulf of Mexico), flume experiments, and numerical modeling are integrated to explore the post-failure behavior of natural and laboratory underwater landslides. At Ursa, failures are retrogressive in that they proceeded from an initial slope failure that creates a headwall region of fault blocks and ridges. As strain accumulates in these blocks and ridges, they progressively weaken until the gravitational driving stress imposed by the bed slope exceeds the resisting shear strength, which allows the material to flow for more than 10 km away from the source area. In a laboratory flume designed for controlled landslides experiments from intact beds of clay, silt, and water, a range of post-failure behaviors from low-mobility failures to high-mobility failures were created. High-mobility failures rapidly accelerate away from the source, create a co-genetic turbidity current, create thin and long deposits with sinuous flow features, and leave behind a relatively smooth and featureless source area. In contrast, low-mobility types move slowly, do not generate a co-genetic turbidity current, and create blocky, highly fractured source areas and short, thick depositional lobes. This work enhances our understanding of geohazards and margin evolution by illuminating coupled processes of sedimentation, fluid flow, and deformation on siliciclastic continental margins.

Speaker Information

Derek leads the Basin Research Lab at the Ohio State University School of Earth Sciences. His research group is dedicated to understanding Earth’s dynamic surface through field, numerical, and lab studies. His group focuses on landslides, gas hydrates, salt tectonics, and earthquakes. Prior to Ohio State, he earned his MS from Penn State University in 2005 and his PhD in 2010 from the University of Texas at Austin. He was then hired as a shallow hazards specialist at ExxonMobil Exploration Company where he worked deepwater exploration and development projects in pore pressure prediction, site characterization, and wellsite pressure surveillance. At Ohio State, his lab combines computational facilities to interpret and process geophysical seismic data and petrophysical data, with the ability to work directly on sediments and cores to measure fundamental physical properties. He works closely with the International Ocean Discovery Program on marine expeditions and as a science evaluation panelist. He is currently working projects offshore North Carolina, Japan, St. John USVI, and methane hydrates in the Gulf of Mexico.