earthquakes recorded in the landscape: using digital topography to investigate earthquake faulting...
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![Page 1: Earthquakes recorded in the landscape: Using digital topography to investigate earthquake faulting Christopher Crosby GEON / Arizona State University SDSC](https://reader030.vdocuments.net/reader030/viewer/2022032523/56649d7f5503460f94a62dac/html5/thumbnails/1.jpg)
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
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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 north…how 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/1906EQ/1906thumb.htmlAnd http://quake.wr.usgs.gov/info/1906/images/fenceoffset_big.html
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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
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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)
• > 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/
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• x,y,z + attributes
LiDAR “point cloud”
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Exercise 2 pdf…
http://lidar.asu.edu/TeacherTech08.html