Previous Story  ||  Headlines  ||  Next Story

Scripps scientists study earthquakes off the coast

Scientists at UC San Diego's Scripps Institution of Oceanography have been depositing instruments on the sea floor to study the Oceanside Fault, which lies 30 miles off the North County shore.

The National Science Foundation is funding the development of the versatile desk-sized instruments, which hold devices for detecting earthquakes. On the side, the Scripps researchers are taking the opportunity to start a longer project to study offshore faults.

On Tuesday, the group dropped the second installment of eight instruments.

"We're trying to get a better assessment as to what kind of activity our offshore faults have here," said Jeff Babcock, the Scripps geophysicist who is leading the project. "What are the seismic hazards? What are the risks?

"This is a reconnaissance mission," he said.

Babcock said the public largely ignores offshore faults, leading to less backing for research in the field. But underwater faults are just as capable of causing earthquakes as other faults, which are the boundaries along which the plates of the planet's crust shift.

The Oceanside Fault, for example, may have been the cause of a magnitude-5.3 quake in 1986 that damaged 50 homes and caused nearly $1 million in damages.

"It's close enough that a magnitude-6.5 or 7 event could do some damage ---- though it's 30 miles off, so it's not likely to do a huge amount of damage," said Peter Shearer, a professor at Scripps who has done land-based studies of offshore faults in the region.

He said motion on the Oceanside Fault could cause a tidal wave. The Oceanside Fault is a thrust fault, where one plate moves above or below another plate at an angle, Shearer said. An upward motion ---- or a temblor-triggered landslide ---- can shift water to create a giant wave.

Such risks make scientists eager to study the many underwater faults up close with ocean-bottom instruments.

"It's hard to get good locations of the offshore events using just the stations that are on land because when you don't have stations that are close to the events, it's hard to be sure what the depths of the events are," said Shearer, who is helping analyze data from the new instruments.

"One of the things we're hoping to improve by having the instruments offshore is that we'll be able to record much closer to the offshore earthquakes."

Babcock said the instruments his team uses have three components: an anchor, four floats and two sensors. The battery-powered instruments store information from the sensors on disks.

One sensor is a seismometer, which detects ground movement. The other sensor is a hydrophone, which detects sound of all sorts ---- from whale songs to earthquakes. Sound is simply vibrations transmitted through a medium such as air, water or rock.

At the end of the experiment, the instruments will release their anchors and return to the surface via the floats.

"As far as testing instruments, if we just put them down in a bland vanilla bottom to see if they worked, that would be just fine," said Babcock. "But by taking advantage of the situation and putting them near faults, we can get a little bit of science out of doing our instrument tests as well."

Babcock said his group will then try to find more money to pursue a study of the shallower Rose Canyon Fault, which runs right along the coast of North County, using other methods.

"By looking at both the bigger faults ---- your Oceanside thrust faults ---- and your smaller faults ---- your Rose Canyon faults ---- we can get a better idea of how much offshore activity we really do have," he said.

Contact staff writer Katie Burns at (760) 740-5442 or kburns@nctimes.com.

8/3/01

Previous Story  ||  Headlines  ||  Next Story