!! DESCRIPTION OF THE EXPERIMENT AND FAQ HERE !!
We're back for now but will probably be offline on the 27th Feb to move the interrogator.
Live waterfall plot of 20 seconds of raw data from a DAS deployment in a dark fibre. The interrogator is located at the Svartsengi Geothermal Power Plant and the cable stretches all the way down to the sea west of Grindavik (see yellow line in the figure). The red line in the top left figure shows the approximate location of the dike intrusion.
An explanation of DAS acquisition for Seismology: www.astronomy.com/science/fib...
Example application in Iceland:
doi.org/10.1029/2022EO220007
For an interactive map of the earthquakes in Iceland: vafri.is/quake/
For more details on what is going on in general, Iceland Met Office: en.vedur.is/
Near real-time spectral analysis of the DAS data: sans.ethz.ch/iceland/
---------------------------------------- FAQ ------------------------------------------------
Q: What is the purpose of this experiment?
A: The purpose of this project is to aid the monitoring efforts of the ongoing unrest by the Icelandic Met Office (IMO: en.vedur.is ). Hopefully, the data will help them to make more informed decisions about the hazards in the area.
Q: What is this data?
A: We are recording ground deformation along the fibre-optic cable. This is raw and unfiltered data, without any processing.
Q: What instrument is used?
A: We use a Silixa iDAS 2 interrogator.
Q: How should I interpret the figure?
A: Time is on the horizontal axis, and the vertical axis is the distance along the cable (location 0 is at the interrogator, and the cable extends from there to the coast). The cable is roughly 8 km.
The colours are proportional to the recorded strength in strain rate. More shaking of the earth will cause higher amounts of deformation and more intense colours.
Q: What are the slanted lines that are continuously present?
A: These are strong noise sources. The upper half of the data is dominated by the noise of the geothermal power plant, which is still operational. The lower half of the figure is dominated by ocean noise, coming from the coast. The lines are slanted as we can see them travel along the cable.
Q: How deep is the cable?
A: This is a dark fibre, we are using a fibre from HS-ORKA, which had already been deployed. Usually, these cables are not too deep: less than a few meters.
Q: What do the earthquakes look like?
A: They are near-vertical lines, typically coloured more intense than blue (yellow, or red). Strong events might appear more intense, last longer, and have clear reverberations.
Q: Do people feel these earthquakes?
A: The intensity of the earthquakes varies a lot, most smaller ones will not be noticeable. We can record these small earthquakes because we are close to their sources, only the larger earthquakes will be felt at further distances.
Q: Are you running any analysis on this data?
A: Yes, except for plotting the data, we also look at the lower frequency content by looking at the past hour of data. We also plot a spectrogram of the past hour of data, and a power spectrum density plot here: sans.ethz.ch/iceland/ . This shows us the frequency content over time and along the cable.
We are currently unable to automatically detect and locate the earthquakes. However, IMO maintains a catalogue with detections, locations and magnitudes, that is automatically created and manually verified: skjalftalisa.vedur.is
Q: Would we be able to see tremor?
A: Whether we can see any tremor in the raw data depends on the strength of the signal, but this would be likely. For example, during the Fagradalsfjall eruption in 2021 we saw the eruption tremor extremely clearly in the data. We also expect tremor to show up in the frequency plots, we especially look to frequencies between 0.7 - 10 Hz. Papers 1 & 2 show examples of DAS data with tremor.
------------------------ RELEVANT PUBLICATIONS --------------------------------------------
Literature from our group:
(1) doi.org/10.1029/2021JB022358
(2) doi.org/10.1785/0320220010
(3) doi.org/10.30909/vol.06.02.30...
cos.ethz.ch/media.html
General DAS literature:
doi.org/10.1785/0220190112
www.nature.com/articles/s4146...
opg.optica.org/jlt/abstract.c...
www.nature.com/articles/s4146...
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