Pacific Northwest Hazards Active
Large earthquakes on the 1100-km-long plate-boundary fault of the Cascadia subduction zone beneath Washington, Oregon, and northern California pose a significant hazard to population centers of the U.S. Pacific Northwest. Tsunamis from a Cascadia megathrust earthquake, and from earthquakes on other trans-Pacific subduction zones, pose a threat along the Pacific Coast in Washington, Oregon, and northern California. Shallow crustal earthquakes also occur regularly.
The Pacific Northwest of the continental United States (Washington, Oregon, and Northern California) faces hazards from three sources of potentially damaging earthquakes:
- subduction zone megathrusts (up to M~9)
- shallow crustal faults (up to M~7.5)
- deep intraplate faults (up to M~7.5).
Large urban centers and infrastructure west of the Cascade Mountains in the Pacific Northwest are susceptible to hazards associated with all three earthquakes sources. East of the Cascade Mountains urban centers and infrastructure are susceptible to long-period motions from Cascadia and strong shaking from local shallow crustal earthquakes. The three largest deep earthquakes in the last century had epicenters near Tacoma and Olympia, WA in 1949 (M7.1), 1965 (M6.5), and 2001 (Mw6.8).
Although paleoseismic studies have shown that multiple great (M8) to giant (M9) earthquakes have occurred on the Cascadia subduction zone in the past few thousand years, we are only beginning to learn about the timing and size of past Holocene earthquakes.
For example, the most recent studies suggest that the recurrence of large earthquakes on the Cascadia plate-boundary fault are irregular and that the magnitudes and locations of the earthquakes are variable. In order to understand how earthquakes in this region are generated, accurately assess the earthquake hazard from specific faults, design cost-effective mitigation strategies, and ultimately forecast future earthquakes, we must reconstruct accurate earthquake histories for the most hazardous faults.
The Pacific Northwest also experiences slow earthquakes and non-volcanic tremor on a regular basis. We conduct basic research aimed at resolving questions concerning the role of these slow earthquakes and tremor in the seismic cycle of the Cascadia subduction zone.
The research of this task aims to learn the timing, location, and size of large prehistoric earthquakes on plate-boundary faults, and the tsunamis that may accompany the earthquakes. More accurate knowledge of these earthquake parameters improves the accuracy of earthquake and tsunami hazard assessment. These parameters are addressed through comprehensive paleoseismology studies along the Oregon, Washington, and northern California coasts. We address the objectives of a multi-year science plan (SZS) to reconcile the onshore and offshore histories of large earthquakes to reduce the uncertainties in earthquake hazard assessment at the Cascadia subduction zone. In FY23 we will evaluate evidence for coastal uplift along the Olympic Peninsula.
Extensive stratigraphic and geomorphic field studies, paleontologic analyses, methods of X-ray and other types of core sediment scanning, dating analyses, earthquake deformation modeling, and tsunami inundation modeling are all important components in developing histories of past earthquakes and their tsunamis.
Large earthquakes on the 1100-km-long plate-boundary fault of the Cascadia subduction zone beneath Washington, Oregon, and northern California pose a significant hazard to population centers of the U.S. Pacific Northwest. Tsunamis from a Cascadia megathrust earthquake, and from earthquakes on other trans-Pacific subduction zones, pose a threat along the Pacific Coast in Washington, Oregon, and northern California. Shallow crustal earthquakes also occur regularly.
The Pacific Northwest of the continental United States (Washington, Oregon, and Northern California) faces hazards from three sources of potentially damaging earthquakes:
- subduction zone megathrusts (up to M~9)
- shallow crustal faults (up to M~7.5)
- deep intraplate faults (up to M~7.5).
Large urban centers and infrastructure west of the Cascade Mountains in the Pacific Northwest are susceptible to hazards associated with all three earthquakes sources. East of the Cascade Mountains urban centers and infrastructure are susceptible to long-period motions from Cascadia and strong shaking from local shallow crustal earthquakes. The three largest deep earthquakes in the last century had epicenters near Tacoma and Olympia, WA in 1949 (M7.1), 1965 (M6.5), and 2001 (Mw6.8).
Although paleoseismic studies have shown that multiple great (M8) to giant (M9) earthquakes have occurred on the Cascadia subduction zone in the past few thousand years, we are only beginning to learn about the timing and size of past Holocene earthquakes.
For example, the most recent studies suggest that the recurrence of large earthquakes on the Cascadia plate-boundary fault are irregular and that the magnitudes and locations of the earthquakes are variable. In order to understand how earthquakes in this region are generated, accurately assess the earthquake hazard from specific faults, design cost-effective mitigation strategies, and ultimately forecast future earthquakes, we must reconstruct accurate earthquake histories for the most hazardous faults.
The Pacific Northwest also experiences slow earthquakes and non-volcanic tremor on a regular basis. We conduct basic research aimed at resolving questions concerning the role of these slow earthquakes and tremor in the seismic cycle of the Cascadia subduction zone.
The research of this task aims to learn the timing, location, and size of large prehistoric earthquakes on plate-boundary faults, and the tsunamis that may accompany the earthquakes. More accurate knowledge of these earthquake parameters improves the accuracy of earthquake and tsunami hazard assessment. These parameters are addressed through comprehensive paleoseismology studies along the Oregon, Washington, and northern California coasts. We address the objectives of a multi-year science plan (SZS) to reconcile the onshore and offshore histories of large earthquakes to reduce the uncertainties in earthquake hazard assessment at the Cascadia subduction zone. In FY23 we will evaluate evidence for coastal uplift along the Olympic Peninsula.
Extensive stratigraphic and geomorphic field studies, paleontologic analyses, methods of X-ray and other types of core sediment scanning, dating analyses, earthquake deformation modeling, and tsunami inundation modeling are all important components in developing histories of past earthquakes and their tsunamis.