Volcano-seismic 2020 unrest in Reykjanes Iceland: The MAGIC multi-parametric rapid response during Covid-19 lockdown

The plate boundary between the American and Eurasian plates runs in southwest Iceland along a 5-10 km wide seismicity zone on the Reykjanes Peninsula. There, tectonic spreading events take place as continuous seismic release and seismic episodes (swarms and individual large events) with recurrence interval of about 40 years and volcanic episodes at intervals of 800-1000 years. The crust in Reykjanes is, therefore, particularly thin and hot and geothermal energy is currently harnesses in two areas on the western part of the peninsula in Reykjanes and Svartsengi.Since January 2020, earthquake swarms with larger events up to M5.6 have been occurring frequently over the entire Reykjanes Peninsula, accompanied by unusual uplift (up to 12 cm) and subsidence cycles in the Svartsengi-Eldv&#246;rp fissure swarm. This raises the question whether we might be at the beginning of a new volcanic episode. In order to classify such processes at an early stage, multidisciplinary geophysical measurements are particularly valuable.The Icelandic Meteorological Office (IMO), University of Iceland as well as ISOR and several partners responded immediately after the unrest began. As soon as January 2020, GFZ proposed a rapid response field campaign (MAGIC: MultidisciplinAry imaGIng and Characterization of the magma/fluid reservoir beneath Svartsengi). Only one week after the uplift start and first earthquake swarm, we connected a Distributed Acoustic Sensing interrogator to a 21 km long telecommunication fibre optic cable which crosses the uplift and swarm area. In addition, while we complied to strict constraints due to the Covid-19 pandemic, the rapid response activities comprised deployment of several additional sensors including broadband seismology, rotational seismology and we performed repeated surveys including gas-, gravity-, electromagnetic-, airborne and ground magnetic- measurements. We present preliminary results from various techniques and discuss their role in discriminating different scenarios aiming at explaining the magma-tectonic unrest phase. In particular, we analyze how the combination of airborne snapshots of ground morphology can be combined with the high temporal and spatial resolution deformation fields along the fibre optic cable.

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The possible role of magma and geothermal fluid in the episodic uplift cycles and intense seismicity beneath the Svartsengi high temperature geothermal field, Iceland

10.5194/egusphere-egu21-7870 ◽

2021 ◽

Author(s):

Ólafur Flóvenz ◽

Rongjiang Wang ◽

Gylfi Páll Hersir ◽

Kristján Ágústsson ◽

Magdalena Vassileva ◽

...

Keyword(s):

High Temperature ◽

Large Scale ◽

Earthquake Swarm ◽

Plate Boundary ◽

Geothermal Field ◽

Plate Boundaries ◽

Clear Trend ◽

Tectonic Event ◽

Fibre Optics ◽

Reykjanes Peninsula

The highly productive high temperature geothermal fields in Iceland are located within active volcanic systems on the plate boundaries. When an earthquake swarm or an unusual surface uplift or subsidence occur, it is important to assess the hazards and whether the unrest is triggered or controlled by volcanic or anthropogenic processes, or a combination of both.On January 22nd, 2020, a rapid, large-scale uplift (14 km x 12 km) started at the Svartsengi geothermal field on the plate boundary of the Reykjanes Peninsula, along with an intense earthquake swarm that began simultaneously about 3 km east of the centre of uplift. The centre of uplift was located about 1 km west of Mt. Thorbj&#246;rn, in the middle of the Svartsengi geothermal field, close to the reinjection wells. Over a period of 6 months, three such uplift cycles occurred, each lasting for several weeks and followed by periods of relatively rapid subsidence. The duration and timing of the uplift-subsidence cycles appears to follow a clear trend where the successive inflation episodes lasted longer but with lower inflation rate.The centres of uplift and the deflation cycles are the same and remained stationary. The accompanied intense earthquake swarms migrated along the 40 km long oblique plate boundary of the Reykjanes Peninsula, demonstrating a major plate tectonic event. The maximum depth of earthquakes was close to 4.5 km directly above the centre of uplift but extending to 6-7 km in the surroundings where the maximum magnitudes reached MW 4.8.A few weeks after the onset of the unrest, nine additional seismic stations were deployed to densify the local seismic network in place. In addition, complimentary data from an existing 21 km long fibre optics cable were used to monitor high-frequency linear strain rates. Both measures led to a significant improvement in the earthquake detection and location which predominantly occurred in swarms. Likewise, InSAR data analysis of temporal uplift cycles was performed, repeated gravity measurements at permanent sites were performed, and resistivity was remeasured at chosen sites. &#160;Multiple different elementary models were developed and tested to explain the cyclic excitation of the uplift, subsidence, and seismicity. While the individual unrest episodes might be controlled by possible magma intrusions into the lower crust, our favoured model explains the spatio-temporal pattern of ground uplift by the rise and diffusion of pore pressure in a 4-5 km deep geothermal aquifer. To distinguish between different models, we use multi-disciplinary geophysical datasets, such as deformation, seismicity, and gravity.

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The 2020 volcano-tectonic unrest at Reykjanes Peninsula, Iceland: stress triggering and reactivation of several volcanic systems

10.5194/egusphere-egu21-7534 ◽

2021 ◽

Author(s):

Halldór Geirsson ◽

Michelle Parks ◽

Kristín Vogfjörd ◽

Páll Einarsson ◽

Freysteinn Sigmundsson ◽

...

Keyword(s):

Earthquake Swarm ◽

Plate Boundary ◽

Tectonic Activity ◽

Volcanic System ◽

Multiple Systems ◽

The North ◽

Stress Changes ◽

Uplift Rates ◽

Source Models ◽

Reykjanes Peninsula

The Reykjanes Peninsula in south-west Iceland straddles the North-America - Eurasia plate boundary and hosts several active volcanic systems, including the Svartsengi volcanic system. The last eruption in this area took place around 1240 CE, with eruptive episodes recurring every 800-1000 years, affecting one volcanic system at a time, but spanning multiple systems &#160;with activity spaced ~100 to 200 years. In January 2020, unrest was identified in Svartsengi, characterized by intense seismicity and inflation at a rate of 3-4 mm per day. This area is located within 5 km of several important infrastructures: a) the town of Grindav&#237;k; b) the Svartsengi geothermal power plant; c) and the Blue Lagoon geothermal spa, which had over a million annual visits before the Covid pandemy.&#160;Two continuously recording GNSS stations were installed in the Svartsengi geothermal area in 2013-2015 to monitor geothermally-induced subsidence.&#160; Coinciding with the onset of an earthquake swarm starting on January 21 (M<4), uplift of about 3-4 mm/day was noticed in automated GNSS and InSAR results. The uplift rates in this first inflation phase decreased after January 31 and reverted to slight subsidence in early February. Interestingly, the most intense seismicity was offset from the uplift center by about 2-4 km to the southeast. Geodetic source models from the initial two weeks indicate the deformation is the result of a sill intrusion at a depth of about 4 km &#160;with a volume change of approximately 3 &#160;million m3. The resulting stress changes from this intrusion act to increase seismicity at the sill edges, thus offering an explanation for why the seismicity is offset from the center of uplift. The location of the sill coincides roughly with a crustal volume with a high Vp/Vs ratio.&#160;Two more inflation-deflation episodes have occurred at Svartsengi in 2020 and the total uplift amounts to approximately 12 cm. Additionally, at least one inflation episode occurred in the Reykjanes system, in February 2020, and inflation started in the Kr&#253;suv&#237;k system in mid-July 2020, culminating in a M5.6 earthquake on October 20. The Fagradalsfjall system, between Kr&#253;suv&#237;k and Svartsengi, has shown high seismicity in 2020, but does not display detectable inflation nor deflation. Therefore, the volcano-tectonic activity in 2020 spans the entire western part of the Reykjanes Peninsula. The stress changes for each of these events are too small to explain the cross-system activity, hence we suggest the entire unrest is &#160;by deep magma migration beneath the entire western Reykjanes Peninsula.&#160;&#160;

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Fibre optic communication subsystem basic test procedures. Fibre optic cable plant

10.3403/01956117u ◽

2015 ◽

Keyword(s):

Fibre Optic ◽

Test Procedures ◽

Fibre Optic Cable ◽

Optic Communication ◽

Basic Test

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Myth: Light Travels to and from the Sample in a Fibre-Optic Cable without Problems

NIR news ◽

10.1255/nirn.1475 ◽

2014 ◽

Vol 25 (6) ◽

pp. 25-26 ◽

Cited By ~ 1

Author(s):

Kim H. Esbensen ◽

Paul Geladi ◽

Anders Larsen

Keyword(s):

Fibre Optic ◽

Fibre Optic Cable

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95/04283 Aerial fibre optic cable systems

Fuel and Energy Abstracts ◽

10.1016/0140-6701(95)95859-4 ◽

1995 ◽

Vol 36 (4) ◽

pp. 300

Keyword(s):

Fibre Optic ◽

Fibre Optic Cable ◽

Cable Systems

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Fibre-Optic Cable Types and Installations

Photonics ◽

10.1201/9780849382949-29 ◽

2017 ◽

pp. 513-528

Author(s):

Abdul Al-Azzawi

Keyword(s):

Fibre Optic ◽

Fibre Optic Cable

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Wave-selective beamforming with Distributed Acoustic Sensing

10.5194/egusphere-egu21-12216 ◽

2021 ◽

Author(s):

Daniel C. Bowden ◽

Sara Klaasen ◽

Eileen Martin ◽

Patrick Paitz ◽

Andreas Fichtner

Keyword(s):

Real Data ◽

Primary Sources ◽

Seismic Sources ◽

Fibre Optic ◽

Wave Type ◽

Matched Field Processing ◽

Fibre Optic Cable ◽

Secondary Scattering ◽

Distributed Acoustic Sensing ◽

Beamforming Algorithm

As fibre-optic DAS deployments become more common, researchers are turning to tried-and-true methods of locating or characterizing seismic sources such as beamforming. However, the strain measurement from DAS intrinsically carries its own sensitivities to both wave type and polarization (Martin et al. 2018, Paitz 2020 doctoral thesis). Additionally, a measurement along a conventional fibre-optic cable only provides one component of motion, and so certain azimuths may be blind to certain types of seismic sources, unless the cable layout can be designed to be oriented in multiple directions.In this work, we explore the development and application of a beamforming algorithm that explicitly searches for multiple wavetypes. This builds on 3-component beamforming or Matched Field Processing (MFP) algorithms by Riahi et al. (2013), and Gal et al. (2018), where in addition to gridsearching over possible source azimuths, a distinct gridsearch is performed for each possible wavetype of interest. This does not solve the problem that a given cable orientation might be less sensitive to certain directions, but at least an array-response function can be robustly defined for each type of seismic excitation. This might help further distinguish whether beamforming observations are dominated by primary sources or by secondary scattering (van der Ende and Ampuero, 2020 preprint).Much of this work uses analytic theory and synthetic examples. Time permitting, the enhanced algorithm will also be applied to data from the Mt. Meager experiment to explore its feasibility and efficacy with real data (EGU contribution from Klaasen et. al, 2021).

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