Fiber optic sensing detects tremor from Icelandic subglacial volcano — ScienceDaily


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Researchers used a fiber optic cable on the ice cap of an Icelandic subglacial volcano to detect low-frequency volcanic tremor, suggesting this expertise could possibly be helpful in monitoring different ice-covered volcano methods.

Their analysis revealed in The Seismic File signifies that the floating ice cap, a part of the Vatnajökull glacier, acted as a pure amplifier of the tremor indicators generated by the Grímsvötn volcano, considered one of Iceland’s most hazardous.

This seems to be the primary remark of a floating ice sheet performing as an amplifier of tremor, mentioned Andreas Fichtner, a professor of seismology and wave physics at ETH Zürich. “Oscillations of ice cabinets in Antarctica or Greenland have been recognized for a very long time,” he defined, “however they’re largely excited by ocean waves.”

Though the precise mechanisms behind volcanic tremor can differ, it may be an indicator of deep volcanic or geothermal exercise, Fichter mentioned. “Along with offering details about the underlying processes, tremor may function a precursor of volcanic eruptions that must be monitored carefully.”

Grímsvötn is considered one of Iceland’s largest and most lively volcanoes, with main eruptions going down on common each ten years. Geothermal heating melts the ice cap, making a subglacial lake on the volcano that sometimes bursts forth and floods the coastal plains. Its explosive eruptions create towering ash plumes that have an effect on agriculture, human well being and aviation. Ash from the final main eruption in Could 2011 closed Iceland’s essential airport and led to the cancellation of 900 flights.

Researchers want to be taught extra concerning the seismic surroundings of Grímsvötn, however putting in a conventional seismic community is pricey and tough within the distant and harsh circumstances on the subglacial volcano. As an alternative, Fichtner and colleagues turned to Distributed Acoustic Sensing.

Distributed Acoustic Sensing, or DAS, makes use of the tiny inner flaws in a protracted optical fiber as 1000’s of seismic sensors. An instrument referred to as an interrogator at one finish of the fiber sends laser pulses down the cable which are mirrored off the fiber flaws and bounced again to the instrument. When the fiber is disturbed by seismic exercise, researchers can study modifications within the timing of the mirrored pulses to be taught extra concerning the ensuing seismic waves.

The researchers deployed a 12.5 kilometer-long fiber-optic cable on Grímsvötn in Could 2021 and picked up information from the DAS system for 3 weeks.

“We needed to know if a big DAS experiment in such a difficult and distant surroundings would really be possible in any respect and if it would educate us one thing new,” mentioned Fichtner. “Now, having analyzed the information intimately, we all know that the discoveries we made wouldn’t have been potential with standard stations. This contains not solely the tremor-related ice sheet oscillations but additionally the practically 3000 native earthquakes that we detected inside the three weeks of the experiment.”

After analyzing the densely sampled DAS information, the researchers realized that the floating ice sheet was performing as a pure resonator of seismic indicators, permitting them to detect the volcanic tremor which may have in any other case been overwhelmed by different ambient or instrument “noise” in a conventional seismic community.

The analysis group acquired fortunate with unusually good climate — together with analysis huts outfitted with a geothermally heated sauna on the best level of the Grimsvötn caldera — in the course of the fiber optic deployment. A trenching sled developed by researchers on the Icelandic Meteorological Workplace, which ploughed and positioned the cable on the similar time, additionally helped.

“The actual problem was splicing within the discipline,” Fichtner recalled. “Since we had three cable drums with 4 kilometers of cable on every of them, we needed to join the fibers, which is named splicing. An optical fiber is thinner than a human hair, and due to this fact it’s tough to deal with on a glacier.”


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