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Researchers develop earthquake sensors using redundant fibre-optic cable

Researchers at the US Department of Energy’s Lawrence Berkeley National Laboratory have developed a use unused fibre-optic cable for long distance earthquake and groundwater mapping.

Unused fibre-optic cable has been developed in to a test bed to give help researchers capture a detailed picture of how earthquakes travel through the earth’s subsurface in California.

According to the researchers only a few seismic sensors have been installed in remote areas of California, which make it hard to understand the impacts of future earthquakes as well as small earthquakes occurring on unmapped faults.

The researchers have turned parts of a 21,000km of unused fibre-optic cable into a sensitive seismic activity sensor that can help the performance of earthquake early warning systems currently being developed in the western United States.

According to Jonathan Ajo-Franklin, a scientist in Berkeley Lab’s Earth and Environmental Sciences Area who led the study, the researcher can tell the difference between a car or moving train versus an earthquake, and to detect both local and distant earthquakes. The technology can also be used to characterise soil quality, provide information on aquifers, and be integrated into geotechnical studies.

dark fiber map cropped

dark fiber map cropped

Source: Ajo-Franklin/Berkeley Lab

Using distributed acoustic sensing (Das) for imaging of the shallow subsurface by measure seismic wavefields by shooting short laser pulses across the length of the fibre, the researchers were able to they were able to detect both local and distant earthquakes, from Berkeley to Gilroy, California, to Chiapas, Mexico

“The coverage of the ESnet Dark Fibre Testbed provided us with subsurface images at a higher resolution and larger scale than would have been possible with a traditional sensor network,” said co-author and a postdoctoral researcher Verónica Rodríguez Tribaldos.

“Conventional seismic networks often employ only a few dozen sensors spaced apart by several kilometers to cover an area this large, but with the ESnet Testbed and DAS, we have 10,000 sensors in a line with a 2m spacing. This means that with just one fibre-optic cable you can gather very detailed information about soil structure over several months.”

Ajo-Franklin added: “Just by listening for 40 minutes, this technology has the potential to do about 10 different things at once. We were able to pick up very low frequency waves from distant earthquakes as well as the higher frequencies generated by nearby vehicles.”

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