Earthquakes recorded in the landscape: Using digital topography to investigate earthquake faulting...
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Transcript of Earthquakes recorded in the landscape: Using digital topography to investigate earthquake faulting...
Earthquakes recorded in the landscape:
Using digital topography to investigate earthquake faulting
Christopher CrosbyGEON / Arizona State University
SDSC TeacherTech SeminarWednesday, February 27, 2008, 4:30pm- 6:30pm
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
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?
San Andreas Fault
• Right-lateral strike slip fault
• Pacific plate moving northwest relative to North America at about 50 mm/yr
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
GPS Network
• Dense network of GPS stations gives us real time information about how the crust of the earth is deforming.
Exercise 1 pdf…
• 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 north…how is the greater deformation rate to the south accommodated?
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
1906 earthquake surface rupture.8’ fence offset above
http://mnw.eas.slu.edu/Earthquake_Center/1906EQ/1906thumb.htmlAnd http://quake.wr.usgs.gov/info/1906/images/fenceoffset_big.html
Reid’s 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
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?
Landforms like this one can yield significant information about EQ behavior
• Wallace Creek development.
Sieh and Wallace, 1987
LiDAR (LIght Detection And Ranging) a.k.a ALSM (Airborne Laser Swath Mapping)
• Airborne pulsed laser scanning system + differential GPS + inertial measurement unit (IMU)
• > 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/mappingchange/
• x,y,z + attributes
LiDAR “point cloud”
Exercise 2 pdf…
http://lidar.asu.edu/TeacherTech08.html