Researchers have been exploring the use of submarine fiber optic cables to observe earthquakes. Now, scientists from the University of California, Lawrence Berkeley National Laboratory, the Monterey Bay Aquarium Institute and Rice University have conducted a four-day study of a 20-kilometer undersea fiber optic cable and recorded a 3.4-magnitude earthquake in the tectonic fault zone off the coast of California.
They found that any interference or movement in fiber optic cables dispersed and distorted the optical signals used to transmit data in fiber optic technology. This “backscatter” phenomenon was observed using a technique called distributed acoustic sensing (DAS), which transforms a 20-kilometer-long cable into an undersea device of 10,000 motion sensors that can detect seismic activity with the accuracy of a pimeter.
DAS technology involves the use of photonic devices to send short pulsed lasers along fiber optic cables and detect backscatter strains caused by stretching strain. These systems are very sensitive to changes in the length of nanometers to hundreds of pimeters per meter.
This is indeed a cutting-edge study of seismology, the first time anyone has used an undersea fiber optic cable to observe seismic signals or to image fault structures. Scientists also highlighted other benefits of using fiber optic cables for seismology, including the need to use thousands of seismographs in applications. The researchers simply walked to the scene and connected the instrument to the end of the fiber. “
As part of the test, scientists were able to record a wide range of seismic waves, including a 3.4-magnitude earthquake 45 kilometers inland near Gilroy, California, and multiple fault maps in the San Gregorio fault system.