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Quake moved whole city: scientists

March 8, 2010
Courtesy of Ohio State University
and World Science staff

The mas­sive earth­quake that struck the west coast of Chile last month moved the whole city of Con­cep­cion at least 10 feet (3 me­ters) to the west, sci­en­tists say. It al­so shifted oth­er parts of South Amer­i­ca that are far re­moved from the cen­ter of the dis­tur­bance.

The pre­lim­i­nar­y find­ings, based on da­ta gath­ered by re­search­ers from four uni­vers­i­ties and sev­er­al agen­cies, il­lus­trate the pow­er be­hind the tem­blor, meas­ured at mag­ni­tude 8.8 and thought to be the fifth-most-pow­erful since mea­sure­ments have been pos­si­ble.

Map showing the move­ments of cities, as re­pres­ent­ed by the red ar­rows, which are exag­gerated in length for visi­bility. The ar­row at the lower right shows the scale, with its length re­pre­sen­ting a 5-cm (2-in) move­ment. A blue star marks the epi­cen­ter of the quake.
Buenos Aires, the cap­i­tal of Ar­gen­ti­na and across the con­ti­nent from the quake’s ep­i­cen­ter, moved West about an inch (2.5 cm), re­search­ers said. Chile’s cap­i­tal, San­ti­a­go, moved about 11 inches (28 cm) west-south­west, and the cit­ies of Val­pa­rai­so and Men­do­za, Ar­gen­ti­na, north­east of Con­cep­cion, al­so moved.

The ep­i­cen­ter was in a South Amer­i­can re­gion that lies in the “ring of fire,” an ar­ea of ma­jor seis­mic pres­sures en­cir­cling the Pa­cif­ic Ocean. Such pres­sures are rou­tinely re­lieved by earth­quakes. Along this ring, the tec­ton­ic plates on which the con­ti­nents move press against each oth­er at so-called fault zones. 

The Feb­ru­ary Chil­ean quake oc­curred where the Nazca tec­ton­ic plate was squeezed un­der, or “sub­duct­ed,” be­low the ad­ja­cent South Amer­i­can plate, ge­ol­o­gists said.

Re­search­ers de­duced the cit­ies’ move­ment by com­par­ing GPS, or 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 or great­er, since the in­i­tial event Feb. 27, cen­tered off the coast of Maule, Chile.

“The Maule earth­quake will ar­guably be­come one of the, if not the most im­por­tant great earth­quake yet stud­ied. We now have mod­ern, pre­cise in­stru­ments to eval­u­ate this event,” said Ohio State Uni­vers­ity earth sci­ent­ist Mike Be­vis, who has led a proj­ect since 1993 meas­ur­ing crus­tal mo­tion and de­forma­t­ion in the Cen­tral and South­ern An­des. The effort is known as the Cen­tral and South­ern Andes GPS Project.
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The massive earthquake that struck the west coast of Chile last month moved the entire city of Concepcion at least 10 feet (3 meters) to the west, scientists say. It also shifted other parts of South America as far apart as the Falkland Islands and Fortaleza, Brazil. The preliminary findings, based on data gathered by researchers from four universities and several agencies, illustrate the power behind the temblor, measured at magnitude 8.8 and thought to be the fifth-most-powerful since measurements have been possible. Buenos Aires, the capital of Argentina and across the continent from the quake’s epicenter, moved West about an inch (2.5 cm), researchers said. Chile’s capital, Santiago, moved about 11 inches (28 cm) west-southwest, and the cities of Valparaiso and Mendoza, Argentina, northeast of Concepcion, also moved. The epicenter was in a South American region that lies in the “ring of fire,” an area of major seismic pressures encircling the Pacific Ocean. Such pressures are routinely relieved by earthquakes. Along this ring, the tectonic plates on which the continents move press against each other at so-called fault zones. The February Chilean quake occurred where the Nazca tectonic plate was squeezed under, or “subducted,” below the adjacent South American plate, geologists said. Researchers deduced the cities’ movement by comparing GPS, or global positioning satellite, locations known prior to the major quake to those almost 10 days later. The US Geological Survey reported that there have been dozens of aftershocks, many exceeding magnitude 6.0 or greater, since the initial event Feb. 27. “By reoccupying the existing GPS stations, CAP can determine the displacements, or ‘jumps’, that occurred during the earthquake,” said Ohio State University earth scientist mike Bevis, who has led a project since 1993 measuring crustal motion and deformation in the Central and Southern Andes. “The Maule earthquake will arguably become one of the, if not the most important great earthquake yet studied. We now have modern, precise instruments to evaluate this event.” The quake occurred off the coast of Maule, Chile. Along with Ohio State University and the University of Hawaii, scientists from the University of Memphis, the California Institute of Technology, and the Chilean institutions Instituto Geografica Militar, Universidad de Concepcion and Centro de Estudios Cientificos are participating in the measuring project. The researchers have built a map showing the relative movement of locations after earthquake.