New Instruments Will Help Scientists Understand Earthquakes
Washington File Staff Writer
Washington - Hundreds of earthquakes occur every day around the globe, most of them underneath the oceans. But most seismometers - the instruments used to record earthquakes - are on land.
Scientists are improving this situation by developing an instrument that records small and large earthquakes on the seafloor, according to a February 22 press release from Woods Hole Oceanographic Institution in Massachusetts.
Jeff McGuire and John Collins at the Woods Hole Oceanographic Institution (WHOI) plan to deploy 40 ocean-bottom seismometers (OBSs) on the seafloor along the East Pacific Rise in the Eastern Pacific Ocean.
The East Pacific Rise is a long north-south ridge made by the spreading seafloor that roughly parallels the Pacific coast of South America. The rise is at the boundaries of some of the vast tectonic plates that make up the Earth’s surface and that lie along the eastern margin of the Pacific Ocean basin.
The new instruments will use a pair of seismometers - one called a broadband seismometer, the other a strong-motion accelerometer - to record ground movements from undersea earthquakes, as seismic arrays do on land.
The seismometers will be placed on the Quebrada/Discovery/Gofar (QDG) transform fault system in the equatorial Pacific Ocean for a year starting in early 2007.
Transform faults are found where two tectonic plates slide past and against each other. Because the edges of the plates are rough, they can catch and hold, allowing stress to build. When the stress is released suddenly, earthquakes can occur.
One of the most famous transform faults is in California - the San Andreas fault – but the technology will have broad application to other fault zones.
The QDG area is known to have large earthquakes, greater than 5.0-magnitude, preceded by foreshocks, or small shocks around 3.0-magnitude, in the last hour before a large rupture occurs.
Current ocean bottom seismometers record moderate ground motions from nearby small earthquakes and can register the foreshocks, but cannot record the main shocks, McGuire said.
McGuire and Collins received a $1 million grant from the W.M. Keck Foundation in California, which supports discoveries in science, engineering and medical research, to develop a new suite of OBSs that accurately can record foreshocks and main shocks.
Ten will be built, for use with instruments from the U.S. National Ocean Bottom Seismograph Instrument Pool (OBSIP), which supplies OBSs to researchers around the country for research projects.
“Together with existing pool instruments and ship time, both supported by the National Science Foundation, we will be able to record large undersea earthquakes directly on top of the faults that generate them,” McGuire said.
Advances in electronics over the past five years, including electronics that need less battery power, have made a new generation of OBSs possible.
The new OBSs will be tested later in 2006 and prepared for deployment on the East Pacific Rise in water depths of 3,500 meters to 4,000 meters.
Information about the Ocean Bottom Seismic Instrumentation Pool is available on a special Web site.
Images of the seismometers are available on the Woods Hole Oceanographic Institution Web site.