Linked Earthquake and Tsunami Hazard Modeling on Puget Sound’s Crustal Faults
Description:
The U.S. Pacific Northwest is home to numerous shallow (≤ 35 km), generally east-west striking crustal faults. Many of these faults, including Washington State’s Seattle Fault (SF), underlie the Puget Sound and have produced earthquakes of ~M6.5–7.8 with subsequent tsunamis throughout the Holocene. Recent paleoseismic investigations found that in 923-24 C.E., the SF and the Saddle Mountain Fault (SMF) either ruptured separately within a span of six months or ruptured together as a combined, multifault rupture with an estimated magnitude of M7.8. An M7.8 multifault rupture exceeds the previously-assumed maximum magnitude for the SF (M7.5) and is not currently represented in regional seismic hazard estimates.
We develop 3-D linked earthquake-tsunami simulations of single- and multifault rupture scenarios on the SF and SMF to quantify their associated ground shaking and tsunamigenesis. Our 3-D physics-based kinematic simulations use the code SPECFEM3D Cartesian to generate synthetic ground motions up to 1.5 Hz. The results demonstrate that an M7.8 combined SF-SMF earthquake would generally produce stronger ground shaking at all periods over a wider region, including in the densely populated eastern Puget Sound area. In both combined rupture scenarios and in single-fault SF scenarios, peak ground velocities can exceed 140 cm/s. Comparisons of our simulated results to NGA-West2 empirical ground motion models show that our simulated results are relatively consistent with observations of global earthquakes. Preliminary simulations of the resulting tsunamis, modeled using the GeoClaw and Method of Splitting Tsunamis softwares, yield wave magnitudes compatible with regional paleotsunami evidence. Together, our linked simulations allow for a time-dependent analysis of earthquake ground shaking and tsunami inundation. They demonstrate the value of linked earthquake-tsunami modeling for improving seismic hazard assessments and for informing engineering design and emergency-planning efforts.
Session: Advancing Seismic Hazard and Risk Assessment through Multi-Disciplinary Approaches [Poster]
Type: Poster
Date: 4/15/2026
Presentation Time: 08:00 AM (local time)
Presenting Author: Julia B. Grossman
Student Presenter: Yes
Invited Presentation:
Poster Number: 42
Authors
Julia Grossman Presenting Author Corresponding Author juliagro@uw.edu University of Washington |
Erin Wirth emoriarty@usgs.gov U.S. Geological Survey |
Audrey Dunham adunham@usgs.gov U.S. Geological Survey |
Ian Stone istone@usgs.gov U.S. Geological Survey |
Randall LeVeque rjl@uw.edu University of Washington |
Loyce Adams lma3@uw.edu University of Washington |
Yong Wei yong.wei@noaa.gov University of Washington, National Oceanic and Atmospheric Administration |
Christopher Moore christopher.moore@noaa.gov National Oceanic and Atmospheric Administration |
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Linked Earthquake and Tsunami Hazard Modeling on Puget Sound’s Crustal Faults
Category
Advancing Seismic Hazard and Risk Assessment through Multi-Disciplinary Approaches