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Scientists seize rare opportunity to map one of largest quakes in recorded history

Scientists will map the rupture site of the 8.8-magnitude earthquake in Chile. Credit and Larger Version

Scientists funded by the National Science Foundation (NSF) and affiliated with the Scripps Institution of Oceanography (SIO) at the University of California at San Diego are undertaking an expedition to explore the rupture site of the 8.8-magnitude Chilean earthquake.

The quake is one of the largest in recorded history.

The scientists hope to capitalize on a unique scientific opportunity to capture fresh data from the event. They will study changes in the seafloor that resulted from movements along faults and submarine landslides. The “rapid response” expedition, called the Survey of Earthquake And Rupture Offshore Chile, will take place aboard the research vessel Melville.  The Melville was conducting research off Chile when the earthquake struck.

“This rapid response cruise is a rare opportunity to better understand the processes that affect the generation and size of tsunamis,” said Julie Morris, NSF division director for Ocean Sciences. “Seafloor evidence of the quake will contribute to understanding similar earthquake regions worldwide.” An important aspect of the rapid response mission involves swath multibeam sonar mapping of the seafloor to produce detailed topographic maps. Data from mapping the earthquake rupture zone will be made public soon after the research cruise ends, Morris said.

The new data will be compared with pre-quake data taken by scientists at Germany’s Leibniz Institute of Marine Sciences (IFM-GEOMAR). Several years ago IFM-GEOMAR researchers conducted a detailed multibeam mapping survey off Chile. Their data will be valuable for comparisons with the new survey to expose changes from the earthquake rupture, say researchers.

“We’d like to know if the genesis of the resulting tsunami was caused by direct uplift of the seabed along a fault, or by slumping from shaking of sediment-covered slopes,” said Dave Chadwell, an SIO geophysicist and chief scientist of the expedition. ”We will look for disturbances in the seafloor, including changes in reflectivity and possibly shape, by comparing previous data with the new [rapid response] data.”

Blog: Research Expedition Off Chile: http://www.siosearch.com/

Fuente -NSF-

The coast of South America is a subduction zone, where the Nazca Plate is plowing under the South America Plate at an average rate of 80 millimeters (3 inches) per year. Their collision gives rise to the spectacular Andes Mountains as well as to devastating earthquakes, such as the 8.8-magnitude quake that struck offshore to the north-northeast of Concepción on February 27, 2010. This map of topography and water depth reveals subduction’s influence on the landscape. Lighter colors indicate higher elevation on land and shallower depth in the water. Quake locations and magnitudes are indicated by black circles. The topography is based on radar data collected during the Shuttle Radar Topography Mission, which flew onboard Space ShuttleEndeavour in mid-February 2002.
The boundary where the two plates converge is marked by a red line, but even without the line, its location would be revealed by the trench located about 100 kilometers (62 miles) offshore. The trench occurs where the Nazca Plate begins its descent beneath the South America Plate. The trench is most sharply defined on the eastern (continental) side: depth plunges rapidly from a few hundred meters (light blue) to several thousand meters (deep blue). In places along their boundary, the two plates may slide easily past each other, but in other locations, they become locked together for a time. Eventually the pressure is too great for the rocks to withstand, and they break. The plates lurch past each other violently: an earthquake. When large quakes occur underwater, the seafloor may heave or sink. The ground movement is what triggers a tsunami.
The Chilean coast has a long history of very large earthquakes. In fact, the February 27 quake occurred about 230 kilometers (140 miles) north of the strongest earthquake ever measured: a magnitude 9.5 event that occurred in 1960. A magnitude 8.5 quake occurred about 870 kilometers (540 miles) farther north in 1922.
References
U.S. Geological Survey. (n.d.). Magnitude 8.8 – OFFSHORE MAULE, CHILE. Earthquake Hazards Program. Retrieved March 1, 2010.

[pers. comment:  Earthquake magnitude was announced by geophysics in scientific paper from march 2009.]

and TIME: Chile Was Prepared for the Quake but Not the Tsunami – TIME

SANTIAGO.- El terremoto que sacudió la zona centro de sur de nuestro país la madrugada del sábado tuvo fuertes repercusiones, no sólo dentro de Chile sino que en todo el mundo.

Porque aparte de las olas gigantes que se reportaron en diferentes países del Pacífico, al parecer el movimiento habría sido tan intenso que habría movido el eje de la Tierra unos 8 centímetros, de acuerdo a Richard Gross, un geofísico de la Nasa, según informó la agencia Bloomberg.

La consecuencia más directa es que el día se podría haber acortado 1.26 microsegundos, según Gross. Agregó que seguramente el eje en el que la masa de la Tierra se balancea se movió unos 8 centímetros. Otros cambios producidos por este temblor, es que las islas pueden haber cambiado su posición. Andreas Rietbrock, profesor de ciencias de la Tierra en la universidad de Liverpool, dice que la Isla Santa María, al frente de Concepción, podría haberse elevado dos metros como resultado del terremoto. Para su cálculo, se basa en el estudio que ha hecho de rocas en el lugar que denotan que con movimientos telúricos pasados la isla ya se había elevado.

Anteriormente, el terremoto en Indonesia de 2004, con una intensidad de 9.1 grados en la escala de Richter, habrían acortado el día en 6.8 segundos, y movió el eje en unos 2.3 millarsegundos. El de Chile, lo movió en 2.7. Esto sucede por el reacomodamiento de la masa de la Tierra producto del movimiento, y se llama el “efecto del patinador de hielo”, ya que al igual que estos patinadores, al acercar sus manos al cuerpo, empiezan a girar más rápido. Algo similar sucede con nuestro planeta.

vía Emol, El Mercurio 01/03/10

[Se hace mención, que el Servicio Sismológico de la Universidad de Chile en nuestro LINKS informa sobre la actividad sísmica nacional en forma automática on line y periódica.]

Actualización  en Abril 2010: El Instituto de Sismología de la Universidad de Chile elaboró un informe técnico el 3 de Abril, que se adjunta aquí mismo.