Earthquake Source-Dependent Amplification of Ground Motions in the Puget Lowland Sedimentary Basins

Date: 4/24/2019

Time: 03:00 PM

Room: Pine

In the Puget Lowland, deep sedimentary basins amplify long-period ground shaking due to earthquakes, increasing the seismic hazard for cities located there. We perform 3-D numerical simulations of point-source earthquakes at many locations throughout the Puget Lowland. We examine the dependence of ground motion amplification in the Seattle and Tacoma basins on earthquake source azimuth and depth, as well as focal mechanism. For periods of 1-10 s, we find that the pattern of ground motion amplification is spatially heterogeneous and varies with the source-to-site azimuth. For close-in earthquakes around the Puget Lowland, the greatest basin amplification occurs towards the far side of the basin. Ground motions from shallow crustal earthquakes experience roughly twice as much amplification compared to the more vertically-incident waves from deeper intraslab earthquakes. Far-field earthquakes on the megathrust generate a different spatial pattern of basin amplification, with the greatest ground motion amplification occurring on the near side of the basin, likely due to differences in path effects or incidence angle. Overall, we demonstrate that the source dependence of basin amplification is an important factor for seismic hazard assessment, both in the Seattle and Tacoma basins, and by analogy, for deep sedimentary basins worldwide.

Presenting Author: Erin Wirth

Authors