Earthquakes recorded in the landscape: Using digital topography to investigate earthquake faulting Christopher Crosby GEON / Arizona State University SDSC.

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