Submarine seismographs

News

A new set of ocean bed seismographs are to be deployed to give a better understanding of basic earthquake processes.

A new set of ocean bed seismographs (OBSs) are to be deployed to give a better understanding of basic earthquake processes. Jeff McGuire and John Collins at the

Woods Hole Oceanographic Institution

(WHOI) plan to set up 40 ocean-bottom seismometers on the ocean floor along the East Pacific Rise in the

Eastern Pacific Ocean

.

The majority of earthquakes in the world occur under the oceans, but most seismographs are on land. As a result, advances in understanding basic earthquake processes have been limited by the available data. Scientists are improving this situation by developing an instrument that records both small and large earthquakes on the seafloor.

The instruments will use a pair of seismometers, one known as a broadband seismometer, the other as a strong-motion accelerometer, to record the ground movements from undersea earthquakes, just like seismic arrays on land. They will be placed on the Quebrada/Discovery/Gofar (QDG) transform fault system for one year starting in early 2007. This area is known to have large earthquakes, greater than magnitude 5, preceded by foreshocks, or small shocks around magnitude 3, in the last hour before a large rupture occurs.

“Although our test area is in the middle of the Pacific Ocean, this technology will have broad application to other faults zones, including those of significant societal relevance such as the nearshore subduction zone off Oregon and Washington,” McGuire said.

Current ocean bottom seismometers record moderate ground motions from nearby small earthquakes and can register the foreshocks, but do not have the range to record the main shocks.

Advances in electronics in the past five years or so, including electronics that require less battery power, have made a new generation of OBSs possible. While some parts of the new OBSs will be bought from commercial firms, other aspects of the instruments will be designed and built by WHOI scientists and engineers. The new generation OBS will be tested this summer and autumn, and prepared for deployment on the East Pacific Rise in water depths of 3,500 to 4,000 metres.