Earthquakes recorded in the landscape: Using digital topography to investigate earthquake faulting

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Earthquakes recorded in the landscape Using
digital topography to investigate earthquake
faulting

• Christopher Crosby
• GEON / Arizona State University
• SDSC TeacherTech Seminar
• Wednesday, February 27, 2008, 430pm- 630pm

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Outline

• Introduction to earthquakes, plate tectonic
  deformation and the San Andreas fault
• Exercise GPS observations of deformation around
  the San Andreas
• Introduction to digital topography, earthquake
  faulting and long and short-term fault
  deformation
• Exercise Google Earth and digital topography to
  document offset features and investigate
  earthquake behavior

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Introduction I

• Goal Develop a basic understanding of plate
  tectonics-driven deformation.
• Questions
• What tools do researchers use to study tectonic
  motion?
• How is plate tectonic motion distributed across
  California where do you expect to have EQs?
• Do our observations of plate tectonics agree with
  where we see earthquakes?

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San Andreas Fault

• Right-lateral strike slip fault
• Pacific plate moving northwest relative to North
  America at about 50 mm/yr

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Plate boundary deformation

• Is all 50 mm/yr of Pacific/North American plate
  motion on the SAF?
• If not, how is this deformation distributed?
• Can use GPS to answer this question

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GPS Network

• Dense network of GPS stations gives us real time
  information about how the crust of the earth is
  deforming.

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Exercise 1 pdf
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• Reverse (or Thrust) faults are found where the
  crust is in compression.
• GPS velocity transect parallel to the SAF shows a
  decline in plate motion to the northhow is the
  greater deformation rate to the south
  accommodated?

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Introduction II

• Goal Illustrate the linkage between plate
  tectonics and evidence for earthquakes in the
  landscape.
• How can high-resolution topography help us study
  earthquakes?
• What do fault related landforms tell us about
  long-term fault activity? What do the landforms
  tell us about short-term fault activity?
• Introduction to the concepts of slip rate, slip
  per event, recurrence and characteristic EQs

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1906 earthquake surface rupture. 8 fence offset
above http//mnw.eas.slu.edu/Earthquake_Center/19
06EQ/1906thumb.html And http//quake.wr.usgs.gov/i
nfo/1906/images/fenceoffset_big.html
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Reids elastic rebound hypothesis Can treat
streams that cross the fault the same way as this
fence
http//quake.wr.usgs.gov/info/1906/reid.html
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• Some terminology
• Slip rate Average rate of motion on the fault
  (mm/yr)
• Slip per event amount of displacement in a
  single EQ
• Recurrence How often does an earthquake occur?
• Characteristic EQ Are all EQs on a fault the
  same size?

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• Landforms like this one can yield significant
  information about EQ behavior

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• Wallace Creek development.
• Sieh and Wallace, 1987

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LiDAR (LIght Detection And Ranging) a.k.a ALSM
(Airborne Laser Swath Mapping)

• Airborne pulsed laser scanning system
  differential GPS inertial measurement unit
  (IMU)
• gt 30,000 points/second
• Ground sampled multiple points/sq. meter
• 15 cm vertical accuracy
• 300 - 500 per sq. km acquisition cost

http//coastal.er.usgs.gov/hurricanes/mappingchang
e/
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LiDAR point cloud

• x,y,z attributes

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Exercise 2 pdfhttp//lidar.asu.edu/TeacherTech0
8.html