Study Reveals More Frequent Earthquake Risk from Seattle's Secondary Faults
Similar Articles
Study Finds Cascadia and San Andreas Faults May Trigger Each Other's Earthquakes
Scientists Identify Natural Braking System That Limits Earthquake Size on Pacific Fault
Scientists Observe Tectonic Plate Tearing Apart for First Time
Alaska Fjord Landslide Triggers Tsunami After Glacier Retreat
Massive Landslide in Alaska Fjord Triggers Record-Breaking Tsunami Wave
New geological research has identified a system of smaller, more active faults beneath the Seattle area. These secondary faults, part of the Seattle Fault Zone (SFZ), appear to rupture roughly every 350 years, with the most recent event likely in the nineteenth century. This finding adds a new layer of seismic hazard understanding for the region's four million residents.
Facts First
- Secondary faults in the Seattle Fault Zone (SFZ) rupture roughly every 350 years, a much shorter cycle than the main fault.
- The most recent rupture likely occurred during the nineteenth century, according to radiocarbon and tree ring evidence.
- Surface ruptures in the last 2,500 years have been dominated by these secondary fault events, says lead author Dr. Stephen Angster.
- The Seattle metropolitan region is home to approximately four million people.
- Scientists used magnetic surveys, lidar, and trenching to study these previously hidden faults.
What Happened
A new study published in GSA Bulletin has examined a system of faults running beneath Seattle and nearby communities. Dr. Stephen Angster, a research geologist at the U.S. Geological Survey's (USGS) Earthquake Science Center in Seattle and the lead author, reconstructed the history of two newly identified secondary faults within the Seattle Fault Zone (SFZ). Findings suggest these smaller faults rupture roughly every 350 years. The most recent rupture likely occurred during the nineteenth century, determined using radiocarbon dating and tree ring evidence from trees that died following an earthquake. Dr. Angster stated that surface ruptures within the SFZ have been dominated by secondary fault events within the last 2,500 years.
Why this Matters to You
If you live or work in the Seattle metropolitan region, this research refines your understanding of local earthquake risk. While the main Seattle fault produces major quakes more than 5,000 years apart, these newly studied secondary faults appear to move more frequently. This could mean a higher probability of ground-shaking events from within the fault system over shorter time scales. The methods used, like lidar to see through forest cover and trenching to date past quakes, help build a more precise hazard map for urban planning and building codes.
What's Next
The study's findings may influence future updates to the National Seismic Hazard Model for the U.S., which has typically excluded shorter faults due to low magnitude potential. Further research will likely focus on mapping other secondary faults in the zone and refining estimates of their potential earthquake strength. Understanding how these smaller faults interact with the larger Seattle Fault Zone (SFZ) is a key next step for assessing the full seismic hazard.