Undersea vehicle installs seismic monitor

By Robert Sanders, Public Affairs

17 April 2002 | Twenty-five miles off the Monterey coast and 3,000 feet down, a remotely operated vehicle, the Ventana, has placed the first permanent broadband earthquake monitor on the California seafloor.

The instrument will help Berkeley seismologists and Mon-terey Bay Aquarium Research Institute geologists measure earthquake activity from the ocean side of the fractured fault zone running up and down the coast. Hopefully, the monitor will reveal new information about seismic activity on the Pacific Plate, which slides past the North American Plate and generates periodic earthquakes.

“It’s hard to look at the plate boundary in detail, and in particular at the San Andreas and San Gregorio faults, without instruments on the other side — the ocean side — of the fault zone,” said project leader Barbara Romanowicz, a professor of earth and planetary science and director of the Berkeley Seismological Laboratory. “Without these types of seafloor monitors, we don’t have good information on the location and depth of earthquakes, and type of faulting involved, or the level of seismic activity on these faults.”

“We have learned from our temporary seismometer deployments that many earthquakes are either poorly located or completely overlooked on the segments of these major faults” added Debra Stakes, a geologist with the Monterey Bay research institute and co-principal scientist on the project.

While scientists and engineers watched aboard the Monterey Bay Aquarium Research Institute’s ship, Point Lobos, the Ventana placed a state-of-the-art digital broadband seismometer on the ocean floor April 9 and deployed a separate recording system the following day. On the next day, the system was instructed to start collecting data.

Romanowicz said the oceans represent a big gap in the global network of seismic monitoring stations, limiting the ability of geophysicists to create three-dimensional pictures of the interior of the Earth.

An off-shore component to Berkeley’s regional broadband network would help seismologists better understand the deep crustal transition zone between the North American and the Pacific plates, as well as associated earthquake hazards, Romanowicz said.

Installation of the monitor is the first of what Romanowicz hopes will be a 20-instrument network comprising an undersea observatory along a portion of the coast where there are no islands. The Berkeley Seismological Laboratory already operates one instrument, which is part of the Berkeley Digital Seismic Network, on the edge of the Farallon Islands. Those islands are part of the Pacific plate 30 miles west of San Francisco.