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

Schöpa, Anne and Chao, Wei-An and Lipovsky, Bradley P. and Hovius, Niels and White, Robert S. and Green, Robert G. and Turowski, Jens M. (2018) Dynamics of the Askja caldera July 2014 landslide, Iceland, from seismic signal analysis: precursor, motion and aftermath. Earth Surface Dynamics, 6 (2). pp. 467-485. ISSN 2196-632X DOI https://doi.org/10.5194/esurf-6-467-2018

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Official URL: https://doi.org/10.5194/esurf-6-467-2018

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 23:24:05 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. The sliding mass was displaced downslope by 1260 ± 250 m. At short periods, a seismic tremor was observed for 30 min before the landslide. The tremor is approximately harmonic with a fundamental frequency of 2.3 Hz 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 2 min before the landslide. We propose that precursory seismic signals may be useful in landslide early-warning systems. The 8 h 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.

Item Type: Article
Uncontrolled Keywords: 2018AREP; IA72
Subjects: 02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
07 - Gold Open Access
Journal or Publication Title: Earth Surface Dynamics
Volume: 6
Page Range: pp. 467-485
Identification Number: https://doi.org/10.5194/esurf-6-467-2018
Depositing User: Sarah Humbert
Date Deposited: 08 Jul 2018 21:31
Last Modified: 08 Jul 2018 21:31
URI: http://eprints.esc.cam.ac.uk/id/eprint/4299

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