The installation of a fiber optic cable atop the ice cap of an Icelandic subglacial volcano by researchers to identify low-frequency volcanic tremor raises the possibility that additional ice-covered volcano systems may benefit from the use of similar technology.
Their study, which was published in The Seismic Record, showed that the Vatnajökull glacier's floating ice crown, one of Iceland's most dangerous volcanoes, served as a natural amplifier of the seismic signals.
According to Andreas Fichtner, a professor of seismology and wave physics at ETH Zürich, this looks to be the first observation of a floating ice sheet serving as an amplifier of tremor.
He noted that although ice shelf oscillations in Antarctica and Greenland have long been recognized, they are often triggered by ocean waves.
Using fiber optics to detect a tremor in an Icelandic subglacial volcano
HALLDOR KOLBEINS/AFP via Getty Images
Although the exact mechanisms behind volcanic tremors can differ, they can be an indicator of deep volcanic or geothermal activity, Fichter said.
"In addition to providing information about the underlying processes, tremor may also serve as a precursor of volcanic eruptions that should be monitored closely," the scientist further noted via ScienceDaily.
Grímsvötn is one of Iceland's largest and most active volcanoes, with major eruptions take place on average every ten years.
Geothermal heating melts the ice cap, creating a subglacial lake on the volcano that occasionally bursts forth and floods the coastal plains.
Its explosive eruptions create towering ash plumes that affect agriculture, human health, and aviation.
Ash from the last major eruption in May 2011 closed Iceland's main airport and led to the cancellation of 900 flights.
Researchers are interested in learning more about the seismic environment of Grímsvötn, but setting up a conventional seismic network is expensive and challenging due to the subglacial volcano's distant location and harsh climate.
Fichtner and associates chose Distributed Acoustic Sensing as an alternative.
The minuscule internal imperfections in a lengthy optical fiber are used as many seismic sensors in a technique called distributed acoustic sensing, or DAS.
At one end of the fiber, a device known as an interrogator, fires laser pulses down the cable, which are reflected off the faults in the fiber and returned to the interrogator.
Researchers can investigate modifications in the timing of the reflected pulses when the fiber is shaken by seismic activity to discover more about the ensuing seismic waves.
After carefully examining the data, the scientists can clearly say that using traditional stations would not have allowed them to make the findings that they did.
This covers both the almost 3000 local earthquakes that they have recorded throughout the experiment's three weeks, as well as the tremor-related oscillations of the ice sheets.
The researchers discovered after studying the highly sampled DAS data that the floating ice sheet was functioning as a natural resonator of seismic signals, enabling them to identify the volcanic tremor that could have otherwise been masked by other ambient or instrument "noise" in a traditional seismic network.
Extrinsic sensing is the process of communicating with an external sensor via a test station over a fiber-optic connection.
Intrinsic fiber sensing, on the other hand, occurs when the fiber itself serves as the fiber optic sensing system.
This form of fiber sensing technology has the advantage of simplifying and being less expensive since distinct connections between the fiber and external sensors are not necessary.
In order to make this conceivable, observable external stimulus, like temperature and strain variations, must affect the light source within the wire.
Raleigh scattering occurs when light photons randomly disperse after interacting with fiber-bound particles.
Since the volume, wavelength, and location of light backscattered to the detector may be used to identify the magnitude and location of attenuation events inside an optical fiber, this approach has proven effective with a variety of fiber testing procedures, including OTDR fiber testing.
Similar variations in photons scattered back to the source in the Stokes band are brought on by temperature in Raman scattering.
The temperature may be precisely measured at any point along the fiber by comparing the intensity of backscattered light in the Stokes and anti-Stokes bands.
