Event Details:

Landslides saturate the landscape of the Pacific Northwest (PNW), USA due to steep topography, a wet climate, proximity to earthquake faults, and weak geologic units. Despite their ubiquity, deciphering cause, frequency, and the geomorphic legacy of PNW landslides remains a long-standing problem in need of new approaches. Several issues have historically limited our progress. Although we know of potential earthquake sources, long recurrence intervals mean that no large magnitude events (≥7 M_w) have been recorded in modern times. Moreover, precipitation landslides happen with each storm and wet season, outpacing and obscuring coseismic slides. Finally, landslide mapping and dating, two fundamental means to probe the landscape record, presents a formidable challenge across Cascadia. In this presentation, I will highlight progress for two case studies: one from Oregon, adjacent the Cascadia subduction zone, and one from the Puget Lowland, adjacent the Seattle crustal fault. In both locations, we use a surface-roughness dating approach to date thousands of deep-seated landslides. In the Puget Lowland, we combine the landslide inventory with new earthquake modeling of the Seattle Fault. Our results indicate relatively few deep-seated landslides in proximity to the Cascadia megathrust and that most deep-seated slides in the Oregon Coast Range originated from rainfall. In contrast, we find evidence of increased sliding around the time of the last major Seattle Fault earthquake. To consider hillslope response to future ground shaking, we modeled both shallow and deep landslides for 18 distinct Seattle Fault earthquakes under wet and dry conditions. We find that all scenarios result in large amounts of sliding, with more translational (10% of slopes) than rotational (4% of slopes) slides. We also find that water saturation and geological strength are more important in terms of landsliding than earthquake properties such as magnitude or hypocenter location. Taken together, these new approaches offer an exciting means to investigate drivers of past landsliding, even many thousands of years later. 

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Dr. Alison R. Duvall is an Associate Professor in the Department of Earth and Space Sciences at the University of Washington, Seattle. She is a geologist and geomorphologist who integrates the broad fields of surface processes and tectonics to tackle a host of questions relating to tectonically driven landscape evolution and geohazards. She and her research team explore these topics at field sites around the world, including New Zealand and the Atacama Desert of Chile, and in locations closer to home, such as Cascadia and the Puget Lowland. Duvall is a PI and core leadership team member of the NSF funded Cascadia CoPes Hub helping coastal communities increase their resilience and increase knowledge about natural hazards and climate change risks. Duvall received the 2016 AGU Luna B. Leopold Award (Earth Surface Processes early career award) for her “contributions to fluvial, hillslope, and tectonic geomorphology that have fundamentally advanced understanding of landscape dynamics across a wide range of scales”. She delivered the 2016 Sharp Lecture in San Francisco at the AGU annual meeting as part of this honor. 

Dr. Duvall earned a BS in Geosciences from Virginia Tech (2000), an MS in Geology from the University of California at Santa Barbara (2003), and a PhD in Geology from the University of Michigan (2011). Following a CIRES (Cooperative Institute for Research in Environmental Sciences) Postdoctoral Fellowship at the University of Colorado at Boulder, she joined the faculty at the University of Washington in Autumn of 2012.

For the Zoom information, please get in touch with Jannis Simões-Seymens (jseymens@stanford.edu)