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https://doi.org/10.5194/esurf-2017-68
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
07 Dec 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Earth Surface Dynamics (ESurf).
Dynamics of the Askja caldera July 2014 landslide, Iceland, from seismic signal analysis: precursor, motion and aftermath
Anne Schöpa1, Wei-An Chao2, Bradley Lipovsky3, Niels Hovius1,4, Robert S. White5, Robert G. Green5,1, and Jens M. Turowski1 1Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, 14473 Potsdam, Germany
2Department of Civil Engineering, National Chiao Tung University, Hsinchu 300, 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. Using data from a network of 58 seismic stations, we characterise a large landslide that occurred at the southeastern corner of the Askja caldera, Iceland, on 21 July 2014, including its precursory tremor and mass wasting aftermath. Our study is motivated by the need for deeper generic understanding of the processes operating not only at the time of catastrophic slope failure, but also in the preparatory phase and during the transient into the subsequent stable state. In addition, it is prompted by the high hazard potential of the steep caldera lake walls at Askja as tsunami waves created by the landslide reached famous tourist spots 60 m above the lake level. Since direct observations of the event are lacking, the seismic data give valuable details on the dynamics of this landslide episode. The excellent seismic data quality and coverage of the stations of the Askja network made it possible to jointly analyse the long- and short-period signals of the landslide to obtain information about the triggering, initiation, timing, and propagation of the slide. The seismic signal analysis and a landslide force history inversion of the long-period seismic signals showed that the Askja landslide was a single, large event starting at the SE corner of the caldera lake at 23:24:05 UTC and propagating to the NW in the following 2 min. The bulk sliding mass was 7–16 × 1010 kg, equivalent to a collapsed volume of 35–80 × 106 m3, and the centre of mass was displaced horizontally downslope by 1260 ± 250 m during landsliding. The seismic records of stations up to 30 km away from the landslide source area show a tremor signal that started 30 min before the main landslide failure. It is harmonic, with a fundamental frequency of 2.5 Hz and shows time-dependent changes of its frequency content. We attribute the complex tremor signal to accelerating and decelerating stick-slip motion on failure planes at the base and the sides of the landslide body. The accelerating motion culminated in aseismic slip of the landslide visible as a drop in the seismic amplitudes down to the background noise level 2 min before the landslide high-energy signal begins. We propose that the seismic signal of the precursory tremor may be developed as an indicator for landslide early-warning systems. The 8 hours 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.

Citation: Schöpa, A., Chao, W.-A., Lipovsky, B., Hovius, N., White, R. S., Green, R. G., and Turowski, J. M.: Dynamics of the Askja caldera July 2014 landslide, Iceland, from seismic signal analysis: precursor, motion and aftermath, Earth Surf. Dynam. Discuss., https://doi.org/10.5194/esurf-2017-68, in review, 2017.
Anne Schöpa et al.
Anne Schöpa et al.
Anne Schöpa et al.

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Short summary
On 21 July 2014, a voluminous landslide entered the caldera lake at Askja, Iceland, and created > 10 tsunami waves inundating famous tourist spots 50 m. 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...
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