In the Pacific Northwest, big faults like the Cascadian subduction zone located offshore get a lot of attention. But big faults aren’t the only ones that pose significant hazards, and a new study in the journal GSA Bulletin investigates the dynamics of a complex fault zone that runs right under the heart of Seattle.
“My job as a paleoseismologist,” says Dr. Stephen Angster, a research geologist at the U.S. Geological Survey’s Earthquake Science Center in Seattle and lead author of the new study, “is to figure out when and how often these local faults rupture, which would help us predict roughly when we come in the window of the next potential rupture.”
The study focuses on the east–west trending Seattle Fault Zone, or SFZ, which cuts through Bainbridge Island and Seattle. Geologists have known for a while that the main fault appears to rupture on timescales greater than 5,000 years, though it’s only in recent years that geologists have begun to map out smaller secondary faults within the SFZ. However, the tools geologists use to calculate earthquake hazards don’t commonly include these smaller, secondary faults, and Angster hopes that learning more about them could help better understand their hazard potential…