CASCADIA SUBDUCTION ZONE Taylor Peacock EPSC 330 Setting: ~1000 kilometers long • Northern Vancouver Island to Cape Mendocino, • California Juan de Fuca plate is subducting under the North • American plate Subduction Zone megathrust earthquakes are very powerful and generate tsunamis. The last great earthquake (M>8) that occurred was just over 300 years ago. 1700 Cascadia Earthquake: Magnitude 9.0 Evidence: groves of red cedar trees killed by saltwater when o subsidence occurred orphan tsunami in Japan (16 feet high) o Tribal history of the coastal First Nations Peoples o Recurrence Interval: Research done at Oregon State University determined that the fault has ruptured 41 times in the last 10,000 years 1/3 chance this will happen in the next 50 • years 19 of these events entailed rupturing along the full length • of the fault 1/10 chance of full margin rupture in next 50 • years Tseax Cone Eruption: Deadliest natural disaster in Canada • Earthquake as a trigger for volcanic eruptions •
Last eruption was between 1668 and 1714 • Carbon dating of wood from trees and based on • historical and magnetic dating Cascadia ruptured 450 km south of Tseax • First Nations told stories of shaking before any fire and • smoke Could the next rupture of of the CSZ trigger a volcanic • eruption in this region? During the event: Initial waves=compressional • May be detected by sensors 30-90s prior to • beginning of shaking Audible to dogs/other animals • Provide warning and to trigger safety procedures • 3-5 minutes of shaking • M 8.0-8.6 if southern portion ruptures and 8.7+ if the • entire length ruptures Several feet of vertical motion and up to 100 feet of • westward motion The wave is estimated to be 20-100 feet tall • depending on where it reaches the coast Impact and Aftermath: 71,000 people in the inundation zone must evacuate between earthquake and tsunami, which is 10-30 minutes. Earthquake and ensuing tsunami is expected to leave • >12,000 people dead and >26,000 injured (FEMA model: early February event) Results: • Fallen bridges will trap people on the coast and • prevent rescue workers from being able to reach them Liquefaction: solid ground behaves as a liquid and • causes instability Highways and roads will be damaged, power will go • out, fires will start ~30,000 landslides will occur in Seattle alone •
They anticipate having to provide food and water for 2.5 • million people, and shelter for 1 million. According to OSSPAC: Improvements in seismic codes since 1994: ~75% of • structures are likely to fail Evacuation procedures + routes • Illegal to build hospitals, schools, firehouses, police • stations in the inundation zone The inundation zone will be ~uninhabitable for years • Time estimates for restoration on the coast: • 3-6 months for electricity • 1-3 years for drinking water and sewage systems • Time estimates for restoration west of Interstate 5: • 1-3 months for electricity • 1-12 months for drinking water and sewer services • 6-12 months for major highways • 18 months for healthcare facilities • Collapse of the economy in the PNW •
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