Is the region where the Chilean quake occurred a major fault area?
The Nazca plate “dives” under the South American plate in the direction of the blue teeth. In red: Feb. 27 fault slip. (USGS) The area where the Nazca plate is being thrust, or subducted, under the South America plate is part of the “ring of fire” that surrounds much of the Pacific Ocean. It gets its name from the volcanoes that form when the subducted material melts and then rises to the surface. The 10 largest known earthquakes, including the recent Chile quake, are all in such subduction zones. Of those 10, five were along the west coast of South America, two were in the Alaska subduction zone, one was along the Russian Kamchatka peninsula, one was in Sumatra, and one was off the Washington and Oregon coast. The last is the only one known from historic records rather than from direct measurements with seismometers. It occurred on January 26, 1700, and was originally recognized by dating the rings of earthquake-downed trees off the coast of the U.S. Pacific Northwest. Later it was da
