Past and Future Coseismic Landslides Triggered by Seattle Fault Earthquakes

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

In this study, we consider coseismic landslides generated from earthquakes along the Seattle Fault, a thrust zone which stretches roughly east-west across the Puget lowland of Washington state. Steep topography, high precipitation, weak glacial deposits, and active crustal faults make Western Washington an ideal site to study the impacts of coseismic landslides. Though the nearby Cascadia subduction zone has the potential to cause large M9 earthquakes, recent work suggests that a smaller earthquake on the Seattle Fault may cause more landsliding in the Seattle area. To better understand the coseismic landslide hazards associated with Seattle Fault ruptures, we will assess the timing of past landslides using a calibrated roughness-age curve and we will make predictions about future coseismic landslides based on modeling of expected ground motions. An inventory of landslides mapped from LiDAR in the vicinity of the Seattle Fault will be dated using a roughness-based metric first calibrated on similar glacial sediments along the western flanks of the Cascades. Using these dates, we can estimate whether slides may overlap in time with the last known rupture on the Seattle Fault ~1100 ybp. To find the areas most susceptible to future coseismic landslides, we will model the expected ground motions for a Seattle Fault earthquake using the finite difference code SW4 and a recently updated crustal velocity model. This code allows us to consider both basin and topographic seismic amplification effects. Ultimately, these modeled ground motions can be used to create a landslide susceptibility map of the area. Together, dated coseismic landslide inventories and landslide susceptibility maps will provide a more complete picture of past and future landslides associated with Seattle Fault earthquakes.

Presenting Author: Erich Herzig

Authors