Plates in Motion

Natural History, April, 1999 by Robert (American businessman and engineer) Anderson

Ever wondered which way the rocks beneath your feet are headed? If so, NASA's Space Geodesy Branch has an Internet site, Tectonic Plate Motion, that will answer the question for you: cddis.gsfc.nasa. gov/926/slrtecto.html. With an array of space-age technologies, scientists are now able to directly measure the movements of the Earth's tectonic plates, which creep along at several centimeters per year. For a great introduction to the subject, try the U.S. Geological Survey's electronic version of its book This Dynamic Earth: The Story of Plate Tectonics (pubs.usgs.gov/ publications/text/dynamic.html).

To watch the plates in motion, go to the University of California Museum of Paleontology's Plate Tectonics site: www. ucmp.berkeley.edu/geology/tectonics. html. It has thirteen animations of continental drift, which--as millions of years flash by in seconds--reveal landmasses sliding around the globe and link to a paleontological history of each era. Be sure to have a look at the museum's page on the German geophysicist Alfred Wegener (www.ucmp.berkeley.edu/history/wegener. html). As early as 1915, Wegener put forth his theory of continental drift, which was met with considerable hostility from his colleagues and not fully accepted until the late 1950s. Another animation, by the University of Texas Institute for Geophysics, can be found at www.ig.utexas. edu/research/projects/plates/plates.mov.

For a good diagram of the modern plate boundaries, go to www-personal. umich.edu/~vdpluijm/plates.gif. The plates, superimposed over a map of the world, show that a large piece of Asia, including part of Japan, rides on the North American Plate. In California the boundary between the Pacific and North American Plates is marked by the San Andreas Fault. One of the most dramatic places to see the fault is at the Point Reyes National Seashore, just north of San Francisco, where the peninsula is literally moving up the coast (www.sfsu.edu/~ geog/bholzman/ptreyes/introgeo.htm). During the disastrous 1906 earthquake, this peninsula, within seconds, lurched one full foot to the northwest.

Robert Anderson is a freelance science writer based in Los Angeles.