IS-NOISE: Rannsókn á breytingum í skjálftabylgjuhraða í íslenskri skorpu, með nýtingu á samfelldu jarðskjálftasuði - verkefni lokið

Fréttatilkynning verkefnisstjóra

11.8.2022

Innan IS-NOISE verkefnisins höfum við kannað nýlega reikniaðferð til að fylgjast með örsmáum breytingum á þessu samfellda suði með það að markmiði að finna mikilvæga undanfara náttúruvár, eins og yfirvofandi eldgos og jarðskjálfta.

Niðurstöður: Með því að rannsaka ákveðin svæði og tímabil áhugaverðrar virkni höfum við getað
greint upphaf eldvirkni þar sem ný kvika hefur troðist inní jarðskorpuna, jafnvel á undan
hefðbundnum vöktunaraðferðum. Við höfum líka óvænt uppgötvað leið til að greina óróa (titring)
sem er falinn í suðinu og er of veikur til að sjást með hefðbundnum aðferðum. Við höfum greint óróa sem tengja má við breytingar á vorin nálægt stórum skriðjöklum. Í eldfjallinu Heklu höfum við einnig greint óróa sem kemur fram árlega í maí og standa yfir til október, þó er ekki ljóst hvað veldur honum.

Áhrif: Í heildina litið benda niðurstöður okkar til þess að aðferðin við að nota samfellt suð til að
fylgjast með breytingum í bergi sé mikilvæg viðbót við vöktun á náttúruvá. Auk útgefinna ritrýndra
vísindagreina í alþjóðleg tímarit, er þýðingarmikil útkoma IS-NOISE verkefnisins fullsjálfvirk úrvinnsla sem keyrir daglega fyrir náttúruvárvöktun á Veðurstofunni og miðar að því að greina breytingar á jarðskjálftasuði. Úrvinnsla er miðuð við helstu eldfjallasvæði á Íslandi, með það að markmiði að greina snemma jarðskorpubreytingar sem geta hjálpað til við að vara við yfirvofandi hættu í framtíðinni. Með farsælli teymisvinnu hefur IS-NOISE verið undanfari Öndvegisverkefnisins IS-TREMOR (Rannís) sem hófst vorið 2021 og miðar að því að fá heildarsýn yfir óróaatburði á Íslandi.

English:

Iceland, like most countries, runs a network of instruments to record earthquakes across the island. These instruments also record continuous ground shaking or noise; data which most often is dismissed. However, within that noise, there is valuable information about waves that have been
scanning the subsurface, waves that are sensitive to variations that occur within the crust and will
change its appearance if the underlying rock experiences unrest. Within the IS-NOISE project, we
have investigated a new computational method to track tiny alterations of this continuous noise with the aim of finding valuable precursors of natural hazards, such as impending volcanic eruptions and earthquakes.

Results: By studying targeted areas and time periods of interesting activity, we have detected the
onset of volcanic activity as new magma entered the brittle crust from below, even before traditional monitoring methods. We have also unexpectedly discovered a way of enhancing weak vibrations, hidden within the noise, too weak to be seen with conventional methods. By analysing locating these tremors we have been able to link them to spring melting of the large outlet glaciers. Hekla volcano also shows vibrations that appear annually during the months May-October, it is however not clear what causes them.

Impact: Our findings show that the method of using continuous seismic noise is an important
addition to the operational natural hazard monitoring. Moreover, In addition to published research papers, a valuable outcome of the IS-NOISE project is a fully automated routine based on continuous records of seismic noise that has been added to the operational natural hazards monitoring at the Icelandic Meteorological Office. The processing scheme runs daily for several areas in Iceland, with the aim of detecting early precursors of crustal changes which may help with warning of impending hazards in the future. With successful teamwork, IS-NOISE has been the prelude to the Grant-of-Excellence IRF project IS-TREMOR which started in spring 2021 and aims at getting a holistic view of tremor events in Iceland.

Information on how the results will be applied
The processing, which has been tuned and follows the best practice according to the findings of this project, is now up and running for the operational monitoring for 6 volcanic areas in Iceland at IMO. The results are already being applied to detect precursors of volcanic unrest. A great example of this, is the ongoing uplift at Askja volcano, one of the most active and powerful volcanoes, capable of producing explosive eruptions which may seriously affect aviation, transportation on land, livestock and human lives, mainly in east Iceland. The operational monitoring aims at firstly detecting precursors and secondly, understanding the spatial extension of the signal. Our dv/v addition to the monitoring is an important addition to the natural hazards monitoring at IMO.

A list of the project’s outputs
● Monitoring products: New real-time products which are running daily for the operational natural
hazards monitoring at the Icelandic Meteorological Office:
o Every minute: Tremv for the monitoring room
o Every minute: Tremv-ALERT for the monitoring room
o Every day: Dv/v monitoring of six different volcanic settings

● Github Open access software:
o Tremv (https://github.com/tremv)
o Tremv-ALERT (https://github.com/tremv)
o MSNoise updates (http://github.com/ROBelgium/MSNoise)

● Peer reviewed Research papers
o 7 accepted or published in open access journals
o 1 in review

● Conference Proceedings
o 7 major global Societies’ or Icelandic conferences proceedings available online

● Report
o VI Report about the TREMV project (2021)

● Websites
o https://is-noise.earth (open access)
o Slack.com (Web-based platform for the project IS-NOISE)
o Twitter: @isnoise1

● Students
In total 7 students:
o 2 MSc thesis
o 1 PhD (in progress)
o 2 BSc students (2019): Rannis Student Innovation Grant, TREMV.
The project was nominated for the presidential awards in 2020
o 2 BSc students (2019): Rannis Student Innovation Grant, Hydroex.
Students studied seismic noise/tremor of hydrothermal explosions
o 2 BSc students (2020): Rannis Student Innovation Grant, TREMV-ALERT

● New Projects: New professional relationships and international collaborative work in Iceland
were added to the IS-NOISE team. In total 3 new projects have been established in addition to 3
new student projects.
o DAS-BúmmBúmm: ETH-Zurich group addition to the IS-NOISE team. Fibre optic cable
deployed in Grímsvötn. Recorded tremor.
o FagraDASfjall: ETH-Zurich group addition to the IS-NOISE team. Fibre optic cable recorded
tremor in Fagradalsfjall.
o IS-TREMOR - Grant of Excellence (2021-2024)
IS-NOISE project led to Grant of Excellence RANNIS project IS-TREMOR

● Workshops
o 3 Workshops (one in Iceland, one in Brussels and one online) with project participants
and other international researchers in the field.

Within the IS-NOISE project; ambient noise-based temporal seismic wave velocity variations (dv/v)
provided significant insights into the 2020 Mt. Þorbjörn-Svartsengi volcanic unrest, also during the
March 2021 Fagradalsfjall eruption. The dv/v variations allowed us to measure differences in the
speed of seismic waves before and after the magmatic activity in the Reykjanes Peninsula. Our analysis was used in near-real time to assist the Iceland Civil Protection Science Board with the joint interpretation of different data sets during the volcanic unrest.

Geothermal analysis
The Hellisheiði geothermal field is located near a triple junction of three different types of plate
boundaries and is both seismically and tectonically very active. The Hellisheiði power plant started
operations in 2016 and injection started in the Húsmúli injection field just northeast of the power
plant in September 2011. As soon as the injection started, seismic activity in the injection field
increased greatly, with thousands of events recorded in the following months. At the time a dense
temporary seismic network was in operation in the area, run by Uppsala University, Massachusetts
Institute of Technology, Reykjavik University, Iceland GeoSurvey, and the Icelandic Meteorological
Office (IMO). We used data from this network to estimate the velocity changes in the injection field
to determine if there is a relationship between the injection of large volumes of geothermal fluid into the subsurface and a change in velocity.

Our first results were promising. A clear decrease in velocity of ~ 0.15% is seen on stations close to
the injection site a few weeks after the injection starts. However, a decrease is also noted on
stations further away from the injection field, indicating that the source of the velocity decrease is
not confined to the injection area. A seasonal change in the microseisms, the source of the signal
used to calculate the velocity change, might be the reason. To explore this further we calculate the power spectrum density for a six-year period of data from six of IMO’s seismic stations. The power
spectrum plots show a clear annual change which shows the different frequency content of the
microseisms, lower frequency in the winter and higher in the summer. The same frequency
pattern is seen on ocean buoys which are located just offshore near Grindavík on the Reykjanes
Peninsula and Höfn in Hornafjörður in the southeast of Iceland.

We are working on re-calculating the velocity changes using correlograms where the seasonal effect has been removed by whitening the time series. Exploring the effect of the change in the microseism on velocity changes could prove useful for future application of the MSNoise method in geothermal areas as well as other types of research.

Heiti verkefnis: IS-NOISE: Rannsókn á breytingum í skjálftabylgjuhraða í íslenskri skorpu, með nýtingu á samfelldu jarðskjálftasuði / IS-NOISE: Investigation of seismic velocity changes in Icelandic crust, using ambient noise
Verkefnisstjóri: Kristín Jónsdóttir, Veðurstofu Íslands, Thomas Lecocq, Royal Observatory of Belgium
Tegund styrks: Verkefnisstyrkur
Styrktímabil: 2018-2020
Fjárhæð styrks: 51,725 millj. kr. alls
Tilvísunarnúmer Rannís: 185209