Transcript Slide 1
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, 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_C enter/1906EQ/1906thumb.html And http://quake.wr.usgs.gov/info/1906/im ages/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 http://coastal.er.usgs.gov/hurricanes/mappingchange/ • ~ 15 cm vertical accuracy • ~$300 - $500 per sq. km acquisition cost LiDAR “point cloud” • x,y,z + attributes Exercise 2 pdf… http://lidar.asu.edu/TeacherTech08.html