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Full-Waveform Inversion of DAS data on a subglacial volcano: Grímsvötn, Iceland

Sara Klaasen 1, Sebastian Noe1, Solvi Thrastarson1, Yeşim Çubuk-Sabuncu2, Kristín Jónsdóttir2, Andreas Fichtner1

  • Affiliations: 1 Department of Earth and Planetary Sciences, ETH Zurich, Zurich, Switzerland 2 Icelandic Met Office, Reykjavik, Iceland

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 121

  • Programme No: 2.1.31

  • Theme 2 > Session 1

Abstract

We present the results of an experiment with Distributed Acoustic Sensing (DAS) on the Grímsvötn volcano in Iceland, and the potential for Full-Waveform Inversion (FWI) with DAS for source properties and Earth structure.   A 12 km long fibre-optic cable follows the caldera rim and ends near the central point of the caldera on top of the subglacial lake above Grímsvötn, where we acquired data for one month (May 2021). Grímsvötn is one of Iceland's most active volcanoes and is covered by the Vatnajökull ice cap.   Here, we discover previously undetected levels of microseismicity, which we locate probabilistically with first-arrival times and the Hamiltonian Monte Carlo algorithm. The ~2000 detected events have local magnitudes between -3.4 and 1.7, and their locations indicate clear clusters of activity near surface expressions of the caldera fault, such as fumaroles and cauldrons. Combined with a starting model that includes the complex topography and ice sheet, we iteratively optimise the moment tensor components and refine the source locations of ~10 high-quality events in the frequency range of 1.5 -- 3 Hz in an FWI workflow. This source inversion is followed by a proof-of-concept study that inverts DAS data for structure with FWI, showing small-scale velocity anomalies related to the geothermal activity of the subglacial volcano.   The combination of state-of-the-art inversion techniques and DAS has the potential to model volcano-tectonic microseismicity and velocity anomalies in great detail, increasing our understanding of subglacial volcanoes and their geothermal dynamics.