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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Volume 6, issue 2 | Copyright

Special issue: From process to signal – advancing environmental...

Earth Surf. Dynam., 6, 467-485, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 14 Jun 2018

Research article | 14 Jun 2018

Dynamics of the Askja caldera July 2014 landslide, Iceland, from seismic signal analysis: precursor, motion and aftermath

Anne Schöpa1, Wei-An Chao2, Bradley P. Lipovsky3, Niels Hovius1,4, Robert S. White5, Robert G. Green5,1, and Jens M. Turowski1 Anne Schöpa et al.
  • 1GFZ German Research Centre for Geosciences, 14473 Potsdam, Germany
  • 2Department of Civil Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan
  • 3Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
  • 4Institute of Earth and Environmental Science, University of Potsdam, 14476 Potsdam, Germany
  • 5Department of Earth Sciences, University of Cambridge, Cambridge CB3 0EZ, UK

Abstract. Landslide hazard motivates the need for a deeper understanding of the events that occur before, during, and after catastrophic slope failures. Due to the destructive nature of such events, in situ observation is often difficult or impossible. Here, we use data from a network of 58 seismic stations to characterise a large landslide at the Askja caldera, Iceland, on 21 July 2014. High data quality and extensive network coverage allow us to analyse both long- and short-period signals associated with the landslide, and thereby obtain information about its triggering, initiation, timing, and propagation. At long periods, a landslide force history inversion shows that the Askja landslide was a single, large event starting at the SE corner of the caldera lake at 23:24:05UTC and propagating to the NW in the following 2min. The bulk sliding mass was 7–16×1010kg, equivalent to a collapsed volume of 35–80×106m3. The sliding mass was displaced downslope by 1260±250m. At short periods, a seismic tremor was observed for 30min before the landslide. The tremor is approximately harmonic with a fundamental frequency of 2.3Hz and shows time-dependent changes of its frequency content. We attribute the seismic tremor to stick-slip motion along the landslide failure plane. Accelerating motion leading up to the catastrophic slope failure culminated in an aseismic quiescent period for 2min before the landslide. We propose that precursory seismic signals may be useful in landslide early-warning systems. The 8h after the main landslide failure are characterised by smaller slope failures originating from the destabilised caldera wall decaying in frequency and magnitude. We introduce the term afterslides for this subsequent, declining slope activity after a large landslide.

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Short summary
On 21 July 2014, a voluminous landslide entered the caldera lake at Askja, Iceland, and created tsunami waves inundating famous tourist spots. The high hazard potential of the site motivated our study in which we analysed seismic data and found a precursory tremor signal intensifying in the 30 min before the landslide. Our paper shows the potential of seismic monitoring techniques to detect precursory activity before a big landslide that could be used for an early-warning system.
On 21 July 2014, a voluminous landslide entered the caldera lake at Askja, Iceland, and created...