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

Abstract

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 15 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 20starting 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 7-16×10 10 kg, equivalent to a collapsed volume of 35-80×10 6 m 3 , 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 25 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 30 frequency and magnitude. We introduce the term afterslides for this subsequent, declining slope activity after a large landslide.Earth Surf. Dynam. Discuss., https://doi

Relations Between the Characteristics of Granular Column Collapses and Resultant High‐Frequency Seismic Signals

“…The seismic signals generated by the granular column collapses have an emergent rise and long decay (Figures b, b, and b) and compare well with seismic signals of landslides and rockfalls observed in the field (Dammeier et al, ; Hibert et al, , ; Moretti et al, ; Pérez‐Guillén et al,; Schneider et al, ; Schöpa et al, ). Similarly, as was previously reported by Farin et al (), on an horizontal slope, the shape of the seismic envelope is symmetrical with respect to its maximum.…”

“…Indeed, the seismic signals of Hibert, Ekström, et al () are recorded far from the flows and seismic signals are in a relatively low frequency range (3‐10 Hz) while particle impacts in the field can generate signals of frequency up to 150 Hz (e.g. Dammeier et al, ; Farin et al, ; Helmstetter & Garambois, ; Hibert et al, ; Hibert, Malet, et al, ; Schöpa et al, ).…”

“…Over the last two decades, seismic signals generated by granular flows (e.g., landslides, debris flows, and rockfalls) have been investigated increasingly as a useful complementary tool to sparse visual observations, in order to detect flows and deduce informations about their localization and dynamics (e.g., Arattano, ; Brodsky et al, ; Dammeier et al, ; Durand et al, ; Huang et al, ; Hibert et al, ; Hibert, Ekström, et al, ; Hibert, Mangeney, et al, ; Kean et al, ; Lai et al, ; Schöpa et al, ; Suriñach et al, ; Pérez‐Guillén et al, ; Yamada et al, ; Zhao et al, ).…”

Earthquake‐Induced Chains of Geologic Hazards: Patterns, Mechanisms, and Impacts

“…Post‐seismic landslides can form at higher rates during heavy rainfall, possibly driven by clearing of oversteepened slopes in the crowns of EQTLs, vegetation and groundwater changes, and altered mechanical properties of bedrock and regolith (Marc et al, ). Oversteepened slopes in the crowns of coseismic landslides contributed less than half of the total post‐seismic landslide volume in documented cases (Schöpa et al, ). Vegetation and groundwater level changes have time scales that differ from those of the post‐seismic landslide transient (<10 years).…”

Towards a standard typology of endogenous landslide seismic sources

“…Yamada et al (2016a); Poli (2017); Helmstetter et al (2017a) argued that the high correlation between the repetitive events could only be explained by stick-slip movement of the locked section(s), while a cracking process would imply a migration of the location of the events and a change in the events waveforms. Schöpa et al (2017) argued that the presence of gliding frequencies could only be produced by similar shown that the number of events is significantly correlated with rainfall and displacement rates (Amitrano et al, 2005;Helmstetter and Garambois, 2010;Walter et al, 2012;Brückl et al, 2013;Tonnellier et al, 2013;Vouillamoz et al, 2017) although some increases of seismicity rates are not correlated to any surface displacement (Helmstetter and Garambois, 2010;Walter et al, 2012;Tonnellier et al, 2013;Vouillamoz et al, 2017 the slow motion and fast acceleration toward failure of unstable slopes. Moreover, the condition of occurrence of precursory seismic events during the nucleation phase of the landslide failure must be also better understand.…”