Earthquakes, volcanic eruptions, tsunamis
(why do we live here?)
Tectonic plates
Tectonic plates:
Juan de Fuca
•  Volcanism the past 37
million years
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Tectonic plates:
Juan de Fuca
•  Volcanism the past 37
million years
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Tectonic plates: Juan de Fuca
Tectonic plates: Juan de Fuca
Tectonic plates: Juan de Fuca
High magnitude (9.0),
damaging eq that cause
tsunamis
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Tectonic plates: Juan de Fuca
Tectonic plates: Juan de Fuca
High magnitude (9.0),
damaging eq that cause
tsunamis
Lower magnitude (5-7), less
damaging eqs that do not
cause tsunamis
High magnitude (9.0),
damaging eq that cause
tsunamis
Lower magnitude (5-7), less
damaging eqs that do not
cause tsunamis
Tectonic plates: Juan de Fuca
Low magnitude
(1-4), hazards
associated with
volcanic activity,
landslides
Subduction zone earthquakes
Low magnitude eq with no
affect on the coast
High magnitude (9.0),
damaging eq that cause
tsunamis
Lower magnitude (5-7), less
damaging eqs that do not
cause tsunamis
Low magnitude
(1-4), hazards
associated with
volcanic activity,
landslides
Shallow
Deep
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Subduction zone earthquakes
Subduction zone earthquakes
Deep EQ
Shallow EQ
•  < 20 miles depth
•  < M7.5
•  Shaking few seconds-1 minute
•  Small aftershocks
•  Tsunamis unlikely
•  < 5 miles depth
•  ~ M9.0
•  Shaking several minutes
•  Many aftershocks up to magnitude 7.0
•  Tsunami will quickly hit Cascadia coast followed by
Alaska, Hawaii & Asia
•  Injuries & fatalities expected in the thousands
•  Previous EQ s
- 1946 Vancouver Island, BC, M7.3
- 1993 Scotts Mills, OR, M5.6
- 1954 Eureka, CA, M6.5
•  Previous EQ s (occur roughly every 500 yrs)
- January 26, 1700 (large tsunami)
- Years 900, 750, 400
Subduction zone earthquakes
2008/09/24 02:33:10 (UTC)
Tsunami warning: http://wcatwc.arh.noaa.gov/
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Subduction zone earthquakes
PNW: Recent earthquakes
•  1949 Olympia, M6.8
- 8 dead, $200 million in damage
•  1962 Corvalis, M4.5
•  1965 Seattle, M6.5
-7 dead, $100 million in damage
•  1976 Pender Island, M5.3
•  1999 Satsop, M5.9
-$10 million in damage
•  2001 Nisqually, M6.8
• 400 injuries, $4 billion in damage
Evidence of M9.0, 1700 event
•  Dead trees caused by 1.5 m coastal sinking
•  Landslides on continental shelf
•  Japanese records of a tsunami
Volcanic eruptions
Volcanic eruptions
Low magnitude
(1-4), damage
associated with
volcanic activity
Recent quakes: http://www.pnsn.org/req2/
Source: USGS
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Volcanic eruptions
Stratovolcano:
Mt. Ranier
Recent quakes: http://www.pnsn.org/req2/
Stratovolcano: Mt. Ranier
9/26/08
All M<2.0
Recent quakes: http://www.pnsn.org/RAINIER/rainrec_eqs.html
Volcanic eruptions:
hazards
Source: USGS
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Volcanic eruptions:
hazards
Volcanic eruptions:
Mudflow
Muddy River, southeast of Mount St. Helens!
Source: USGS
Volcanic eruptions:
Mudflow
Source: USGS
Volcanic eruptions:
Mudflow
Along Cowlitz River
Mount St. Helens, 1982!
Source: USGS
Source: USGS
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Volcanic eruptions:
Pyroclastic flow
Volcanic eruptions:
Pyroclastic flow
Mt. St. Helens, 1980
17 pyroclastic flows, moving over 60 mph and 800°F
Source: USGS
Volcanic eruptions:
Tephra flow
Source: USGS
Volcanic eruptions:
Tephra flow and ash fall
Mt. St. Helens, 1980
Total volume of ash enough to cover a football field
to a depth of 150 miles!
Source: USGS
Source: USGS
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Volcanic eruptions:
Tephra flow and ash fall
Mt. St. Helens, 1980
Total volume of ash enough to cover a football field
to a depth of 150 miles!
Source: USGS
Tectonic plates: Juan de Fuca
Tectonic plates: Juan de Fuca
Low magnitude eq with no
affect on the coast
Recent offshore: http://www.pmel.noaa.gov/vents/acoustics/seismicity/nepac/recent.html
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Tectonic plates: Juan de Fuca
Axial seamount
•  700 m tall
•  volcanically active
Tectonic plates: Juan de Fuca
Juan de fuca ridge
Axial seamount
•  700 m tall
•  volcanically active
Juan de fuca ridge
ASHES hydrothermal vent field
•  Discovered in 1984
•  4 sulfide chimneys, 5m high
•  1550 m deep
Source: NOAA
Seattle Fault
http://www.pmel.noaa.gov/vents/nemo/explorer/bio_gallery/biogallery1.html
http://www.pmel.noaa.gov/vents/nemo/explorer/ashes.html
Source: NOAA
Seattle Fault
Source: USGS
Source: USGS
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Seattle Fault
Seattle Fault
•  Thrust fault
•  Thrust fault
9 m of uplift
over 16,000 yrs
S
N
Source: USGS
Seattle Fault
Source: USGS
Seattle Fault: Events
•  900 AD M 7.0 eq
- 7m uplift
- Puget Sound tsunami
- Landslides lake WA
- Rock avalanches in
Olympic Mtns
•  Thrust fault
•  Recurrence
- 10,000s of years
Source: USGS
Source: USGS
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