This Week and next

1
This Week (and next)

• Today
• Reminder about co-op final exam
• Seismic Hazards (what quakes do)
• Friday Earthquakes seismic waves
• Monday Holiday
• Wednesday
• Plate Tectonic theory

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Announcements

• Defenses due today by 5 pm in ES 240

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Todays Plan

• Seismic risks
• Earthquakes
• Tsunamis
• Types / sources of quakes around here
• Quake prediction

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Seismic Hazards

• Where is there high earthquake frequency?

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What kinds of seismic hazards are there?

• Quakes (ground shaking)
• Tsunamis
• Landslides
• Volcanic eruptions?

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Seismic Risk

• Where is there high earthquake risk?
• Risk Probability x Consequence
• New Madrid
• Probability 90
• of M6.0 by 2040
• Consequence
• Building codes in area
• not quake-conscious

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Quake locations in PNW

• focus or epicenter?

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PNW Seismic Network
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Sources of quakes in PNW

• Shallow earthquakes (e.g. Seattle fault or N.
  Whidbey Island fault)
• Deep (Benioff) earthquakes
• up to M 7.5
• Subduction zone (megathrust) earthquakes

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Sources of quakes in PNW

• Shallow earthquakes (e.g. Seattle fault or N.
  Whidbey Island fault)
• Deep (Benioff) earthquakes
• up to M 7.5
• Subduction zone (megathrust) earthquakes

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1. Shallow Puget Sound Faults
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Paleoseismology radar photo(Bainbridge Island)
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Sources of quakes in PNW

• Shallow earthquakes (e.g. Seattle fault or N.
  Whidbey Island fault)
• Deep (Benioff) earthquakes
• up to M 7.5
• Subduction zone (megathrust) earthquakes

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Sources of quakes in PNW

• Shallow earthquakes (e.g. Seattle fault or N.
  Whidbey Island fault)
• Deep (Benioff) earthquakes
• up to M 7.5
• Subduction zone (megathrust) earthquakes

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2. Deep Nisqually (M6.8) 2/28/01
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Deep quake locations in PNW
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Sources of quakes in PNW

• Shallow earthquakes (e.g. Seattle fault or N.
  Whidbey Island fault)
• Deep (Benioff) earthquakes
• up to M 7.5
• Subduction zone (megathrust) earthquakes

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Sources of quakes in PNW

• Shallow earthquakes (e.g. Seattle fault or N.
  Whidbey Island fault)
• Deep (Benioff) earthquakes
• up to M 7.5
• Subduction zone (megathrust) earthquakes

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Sources of quakes in PNW

• Shallow earthquakes (e.g. Seattle fault or N.
  Whidbey Island fault)
• Deep (Benioff) earthquakes
• up to M 7.5
• Subduction zone (megathrust) earthquakes
• Up to M 9.5 !!!

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Sources of quakes in PNW

• Shallow earthquakes (e.g. Seattle fault or N.
  Whidbey Island fault)
• Deep (Benioff) earthquakes
• up to M 7.5
• Subduction zone (megathrust) earthquakes
• Up to M 9.5 !!!
• Last one on Jan. 26, 1700 (at 9 PM)

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Sources of quakes in PNW

• Shallow earthquakes (e.g. Seattle fault or N.
  Whidbey Island fault)
• Deep (Benioff) earthquakes
• up to M 7.5
• Subduction zone (megathrust) earthquakes
• Up to M 9.5 !!!
• Last one on Jan. 26, 1700 (at 9 PM)
• How do you know that?

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Ghost forest (red cedar) at Copalis R.
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Origin of ghost forests
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Age of ghost forests
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Evidence of tsunami in Oregon marsh (dated 1700
AD)
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Tsunami and subsidence evidence from CA to BC

• But why subsidence?

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Cascadia Subduction Zone
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Oral Evidence

• In the days before the white man there was a
  great earthquake. It began about the middle of
  one night and continued about 20 hours, when it
  ceased.
• Excerpted from a story told by a Cowichan elder
  to James Hill-Tout in the early 1900's and
  included in his Report on the South eastern
  tribes of Vancouver Island (Maud, R. (1978) The
  Salish People, Volume IV)

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Map of Kuwagasaki Japan, site of tsunami in 1700
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Simulation of tsunami from 1700 Cascadia
earthquake
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Cascadia Subduction Zone
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How often do megathrust earthquakes occur?

• In the Cascadia subduction zone 13 megathrust
  events have been identified in the last 6000
  years, an average one every 500 to 600 years.
  However, they have not happened regularly. Some
  have been as close together as 200 years and some
  have been as far apart as 800 years. The last one
  was 300 years ago.

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How big can they be?

• Megathrust earthquake are the world's largest
  earthquakes. The last Cascadia earthquake is
  estimated at magnitude 9. A megathrust earthquake
  in Chile in 1960 was magnitude 9.5, and one in
  Alaska in 1964 was magnitude 9.2.

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Seismic Risk Maps

• Help predict damage
• Plot accelerations of the ground that might be
  produced by a quake of a specific magnitude
• peak accelerations plotted as of g (9.8 m/s2)
  
• so 100 can bounce an object off the ground

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Hazard maps are a prediction

• How can we predict quakes? (WarmUp)
• What type or types of quake forecasting is (are)
  reliable?
• long-term forecasts
• using seismic gaps 73
• short-term forecasts
• using animal behavior 0
• short-term forecasts
• using groundwater levels 2
• all of the above 24

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Hazard maps are a prediction

• How can we predict quakes?
• Need info on past quakes
• Historical
• Pre-historical (folklore)
• Paleoseismology

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Paleoseismology LA exampleCharlie Rubins
trench
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Paleoseismology LA example
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Paleoseismology LA example
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Paleoseismology LA example

• Examining set of quakes and offsets gives
  frequency of various size quakes over recent
  geologic time.
• Offset of at least 10 m for two EQ in the last
  13,000 years
• 5 m offset would produce M 7.2 earthquake in
  metropolitan LA
• recall that the countrys most expensive natural
  disaster (Northridge 1994) was M 6.7

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EQ Prediction

• Two time scales
• long term (decades to centuries)
• short term (hours/days/years)
• Long term predictions based on seismic gaps
• Turkey example
• prediction in 1997 (12 in next 30 yr)
• Ismet EQ (M7.4) in August 1999

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Long Term Prediction
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Long Term Prediction
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Long Term Prediction
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Ismet 3m strike-slip offset
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Ismet damage and deaths
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Short Term Prediction

• Relies on recognition of precursors
• land deformation
• increased seismic activity
• geomagnetic and geoelectric changes(affects
  animal behavior?)
• groundwater level changes
• None works!

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Short-term predictions

• Parkfield, CA
• M6 quakes every 22 years

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Parkfield EQ prediction project

• Between creeping and locked sections of the SAFZ

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Parkfield EQ prediction project

• Tons of instruments waiting since 1985 for next
  M6
• (Expected by 1993)
• ...still waiting...