photo credit: USGS; photo by D. Cavit; image source

Imperial Valley Earthquake

The photo (hi-res version) shows sideways movement in a plowed field in Imperial Valley, California, following the magnitude 6.5 earthquake there in 1979.  You can see other photos such as offset of a woodpile. To learn about the fault in California that runs near San Francisco and Los Angeles, visit San Andreas Fault.

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Faultline

Visit the Exploratorium's Faultline to learn about the great 1906 San Francisco earthquake and how our understanding of seismology has progressed since then. Don't miss the activities in "Active Zone," especially "Cookie Subduction" and "Liquifaction."

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images courtesy of USGS; image source

USGS: Earthquake Center

These images (hi-res version), from the U.S. Geological Survey, show earthquakes around the world during April 10-16, 2007. Even over this short time, the outline of the "ring of fire" is clear. To learn more, visit Savage Earth: Earthquakes from PBS, and Understanding Plate Motions from USGS.

Earth's Inconstant Magnetic Field

Earth's magnetic field has reversed quite a number of times--see NASA's Earth's Inconstant Magnetic Field for an overview and a model of how this reversal occurs. These reversals produced magnetic patterns on moving plates at the mid-Atlantic Ridge, as described in The Mobile Crust. For a timeline of the many reversals, see When Compasses Point South.