A Stanford University team of scientists has been working on developing a new way of detecting earthquakes, more in advance, by using already existing technology.
To do so, the researchers took a look at optic fiber cables and considered the possibility of using them instead of the already utilized seismometers.
Optical Fibers, and the Utility of Their Sensitivity
Currently used seismometers function by picking up the tremors of the earth. However, they are also somewhat short-ranged, and their alert time is rather short.
The Stanford study changed direction and decided to take a look at an existing technology that is already underground and very sensitive.
Internet-transmitting optical fibers “bounce” light signals down a glassy cable. As they do so, they can also register and then measure any minor disturbances to the signal as is coming back. The technology, in itself, is called distributed acoustic sensing or DAS and is currently being used by the gas and oil industries.
“If the fiber were totally stationary, that ‘backscatter’ signal would always look the same. But if the fiber starts to stretch in some areas — due to vibrations or strain — the signal changes,” explains Eileen Martin, the study co-author.
The study team decided to test the possible utility of optical fibers in monitoring and measuring earthquakes. To do so, they installed three miles of such fibers, shaped in a figure eight, under Stanford. These were also fitted with laser interrogators, which helped record their every movement.
This technology was called optic seismic observatory by the team and has been active since September 2016. It has captured over 800 seismic events since then, in just a year of operation.
The seismic observatory has been detecting anything from small rumbles to big magnitude events, such as the 8.2 magnitude earthquake on September 08, in Mexico.
It can also distinguish between different kind of waves, from S to P ones. These are shockwaves that pass through the grounds at different speeds. Usually, P waves arrive earlier than S ones, so capturing them might help detect earthquakes earlier.
As such, this might be ‘an effective early warning system’. Still, this research is still in its early stages, and the optic fibers are rather less sensitive than the currently used seismometers.
Details on the current study findings are available in the SEG Technical Program Expanded Abstracts 2017.
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