Seafloor Seismometers

Robot-Placed Instruments Are Recording
Earthquake Waves From Under the Waves

An international team of scientists and technicians working on the Monterey Bay Ocean Bottom International Seismic Experiment (MOISE) have succeeded in installing a unique combination of scientific instruments on the seafloor.

The first ever deployment of instruments of this size and type by a remotely operated vehicle, MOISE, is part of a global effort to eventually set up seafloor observatories for continuous monitoring of geological activity such as earthquakes.

"The long term goal is to put these packages all over the ocean floor to obtain a better understanding of global seismic events and seismic activity at plate boundaries like that off the California coast," says Barbara Romanowicz, professor of geology and geophysics and director of the campus's Seismographic Station.

Romanowicz originally conceived the idea of placing seismometers on the ocean floor more than a decade ago while heading a French government project to study the Earth's interior. Her former colleagues there are now her collaborators on the MOISE project, from the Institut de Physique du Globe and Division Technique of the Institut National des Sciences de l'Univers.

"If we are ever going to realize the goal of establishing observatories to provide continuous access to the remote ocean floor, then we must learn to deploy these instruments from remotely operated vehicles," says Debra Stakes, geologist and chief scientist at the Monterey Bay Aquarium Research Institute.

Using the Monterey institute's research vessel R/V Point Lobos and its tethered remotely operated vehicle, Ventana, the team has deployed the instruments at a site about 1,015 meters deep in Monterey Bay, 40 km offshore and 10 km west of the San Gregorio fault, which runs from south of Point Reyes to Big Sur. The equipment, which can register both global and local seismic events, will be left at the site to record data until it is recovered in September by Ventana. The centerpiece of the MOISE instrument group, a broadband seismometer similar to ones that serve as the backbone for the global seismic network, was made available by the French collaborators.

About 20 broadband seismometers, which can register sound waves with periods from one-tenth of a second to 100 seconds, are located around Northern California. All but one-an instrument in the Farallon Islands-are at land-based seismic stations on the eastern side of the boundary zone between the Pacific and North American tectonic plates.

A record of seismic signals from the MOISE site, which lies on the western side of the plate boundary zone, will complement data from existing earthquake monitoring stations, allowing scientists to determine more accurately locations of seismic events off the Central California coast. The MOISE data will also add to the Monterey Bay Aquarium Research Institute's study of offshore faults of the westernmost San Andreas system.



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