In addition to sending films, emails, and tweets, fiber-optic cables that go through the ground, along the seafloor, and into our houses have other uses. Anywhere the wire reaches the ground, these signals can also capture ground vibrations as small as a nanometer. Fiber-optic cables have long been used for unanticipated purposes, but only a small number of military and commercial applications have taken use of it.

In a pilot study at the University of Washington, fiber optic sensing is being investigated for seismology, glaciology, and even urban surveillance. The new UW Photonic Sensing Facility is supported in part by a $473,000 grant from the M.J. Murdock Charitable Trust, a non-profit organization based in Vancouver, Washington. It has three decoder devices, or "interrogators," that use photons traveling through a fiber-optic cable to detect ground motions as small as 1 nanomeeter.

According to principal investigator Brad Lipovsky, an assistant professor of Earth and space sciences at the University of Washington, fiber-optic sensing represents the greatest development in ground-based geophysics since the discipline turned digital in the 1970s.  The potential of this technology will be investigated by the UW Photonic Sensing Facility and its collaborators in a variety of scientific domains, such as seismology, glaciology, oceanography, and infrastructure and hydrology monitoring. 

The new facility is one of a few research centres across the world that are starting to look at fiber optics for sensing ground motion. It is the largest in the United States and the first of its kind in the Pacific Northwest. The amount of seismic data could increase thousands of times as a result of this monitoring strategy. For now, one of the three UW interrogators is connected to a "dark fiber", or unused cable, that connects the  campuses of Seattle University and Bothell.To detect volcanic, oceanic, glacial and tectonic systems in Alaska,  researchers will soon connect to a similar undersea cable running through Cook Inlet. The other apparatus will be deployed momentarily.

Seismic waves spread out from the source of the vibration, whether it be from an earthquake, a large truck, or building activities. A very small strain in the fiber optic cable caused by a seismic wave disrupts the photons that are normally reflected back to the source.The location of the cable disruption can be identified by  researchers by detecting this break in the returning light waves.

Because the system is dispersed and can track both sound waves and ground motion, it is known as "distributed acoustic sensing," or DAS.It is also possible to capture more slow motion using the same approach. Glacier expert Lipovsky and UW doctoral student John-Morgan Manos brought equipment up to Mount Baker's Easton Glacier to track the pace of surface melt. To determine how much snow was melting on the glacier, the team installed a cable and used an interrogator.

UW scientists working with the Pacific Northwest Seismic Network are investigating various seismology applications, such as earthquakes, volcanoes, and landslides. UW oceanographers will monitor ocean faults and possibly listen for whales using fiber optic cables connected to an underwater observatory. If this technology could track building and bridge infrastructure, traffic collisions, or both, UW civil engineers will investigate.Semi-permanent observatories in Seattle and other underutilized "dark" fibers, such as a cable running to Whidbey Island, will be  part of the facility. The team is also looking into projects farther away at a fjord in Greenland and at McMurdo Station in Antarctica. They also intend to construct cables for temporary field deployments at Mt. Rainier.

According to Marine Denolle, an assistant professor of Earth and space sciences at the University of Washington, "we're getting to the'smart Earth' concept, where we can listen to the Earth.  "With the help of this technology, seismic sensing may now be used in locations where it was previously impossible or prohibitively expensive to deploy sensors. The other component that is novel is a higher sensor density than before. While fiber optic cables take measurements at different locations along the cable, modern seismometers only record ground motion at one location.The test cable includes 15,000 data channels.Denolle will analyze this new  seismic data stack using computation and machine learning.

Denolle stated, "In seismology, our data used to be merely wiggles. This is the first time that 2D graphics and even films of flowing data are available. Awarded in late 2021, the grant. Last spring, researchers used the funding to connect and test the equipment, and a data-visualization room will shortly be built on campus.

The University of Washington is the first university to have acquired this much equipment for this method thanks to funding from the M.J. Murdock Charitable Trust, according to Lipovsky. We are eager to see where this goes even though it is still in the pilot experiment stage.
The UW and the UW-based Pacific Northwest Seismic Network are other funders.