Chilean earthquake actually moved cities.

• Position: Geography

The massive magnitude 8.8 earthquake that struck the west coast of Chile in February moved the entire city of Concepcion at least 10 feet to the west, and shifted other parts of South America as widespread as the Falkland Islands and Fortaleza, Brazil. The preliminary measurements, produced from data gathered by researchers from four universities and several agencies, including geophysicists on the ground in Chile, paint an extreme picture of the power behind this temblor, believed to be the fifth-most powerful since instruments have been available to measure seismic shifts.

Buenos Aires, the capital of Argentina and across the continent from the quake's epicenter, moved about one inch to the west, and Chile's capital, Santiago, shifted about 11 inches to the west-southwest. The cities of Valparaiso and Mendoza, Argentina, northeast of Concepcion, also readjusted significantly.

The quake's epicenter was in a region of South America that is part of the so-called "ring of fire," an area of major seismic stresses that encircles the Pacific Ocean. All along this line, the tectonic plates on which the continents move press against each other at fault zones. The Chilean quake occurred where the Nazca tectonic plate was squeezed under, or "subducted," below the adjacent South American plate. Quakes routinely relieve pent-up geologic pressures in these convergence zones.

The research team deduced the cities' movement by comparing precise global positioning satellite locations known prior to the major quake to those almost 10 days later. The U.S. Geological Survey reported that there have been dozens of aftershocks, many exceeding magnitude 6.0 since the initial Feb. 27 event.

Mike Bevis...