A research team led by a UC Berkeley doctoral student found that marine fiber-optic cables could be used to detect seismic waves and record information on earthquakes that occur far offshore.
In the study — published in Science magazine — researchers from campus, Rice University, the Monterey Bay Aquarium Research Institute and the Lawrence Berkeley National Laboratory, or Berkeley Lab, established a 20-kilometer-long seismological array to record geological data along the ocean floor. According to campus doctoral student and lead author Nate Lindsey, the study showed how fiber-optic cables could be used as seismic sensors in areas that were previously unexplored.
“Today, land surveys may involve hundreds of seismic stations covering, but in the oceans it is too expensive to achieve this type of station coverage,” Lindsey said in an email.
Most of the networks that exist to monitor seismic activity are on land, according to Lindsey. The use of these marine fiber-optic cables would allow scientists to expand these networks beyond the shoreline to the ocean floor.
The fiber-optic cable used in the study relies on a technique known as Distributed Acoustic Sensing, or DAS.
According to Jonathan Ajo-Franklin, a professor of geophysics at Rice University and faculty scientist at Berkeley Lab, DAS utilizes short bursts of laser light to measure any disturbances or strain on the cable caused by vibrations. This would, in turn, provide detailed information on any seafloor seismic activity.
The cable had a total of 10,000 seismic stations spaced 2 meters apart, which, according to Lindsey, is much more than the number of stations involved in conventional marine geophysics methods. He added that the most common method of recording information from the seafloor relies on using only a few stations across a large area.
One important aspect of using fiber-optic cables is their ability to record large amounts of information over a short period of time, Lindsey said in the email. In the study, the array was able to generate about 3.5 terabytes of data in the span of four days, with each component recording 500 samples every second.
Ajo-Franklin added that these fiber-optic cables could be used to analyze more than just seismic waves.
“The cable can be used to measure the waves from local or distant earthquakes as well as processes in the water column, such as ocean waves, or seismic waves which travel along the ocean floor,” Ajo-Franklin said in an email. “Anything which generates a vibration can be recorded including the sounds of the surf or ships.”
During the experiment, researchers were able to record information on a minor earthquake that occurred in Gilroy, California. According to Lindsey, the data collected by the marine array allowed scientists to determine the location of both known and previously unidentified seafloor fault lines.