CASCADIA SUBDUCTION ZONE Taylor Peacock EPSC 330 Setting: ~1000 - - PDF document

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

• ver 300 years ago.

1700 Cascadia Earthquake:



Magnitude 9.0



Evidence:

• groves of red cedar trees killed by saltwater when

subsidence occurred

• rphan tsunami in Japan (16 feet high)
• Tribal history of the coastal First Nations Peoples

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
• f 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
• ut, 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