Evidence of log-periodic oscillations and increasing icequake activity during the breaking-off of large ice masses

Faillettaz, Jérôme; Pralong, A.; Funk, Martin; Deichmann, Nicholas

doi:10.3189/002214308786570845

Cited by 45 publications

(89 citation statements)

References 27 publications

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“…Despite this complication, the study of basal icequakes is highly valuable to a variety of glaciological aspects. These seismic signals can be related to stick-slip motion (Weaver and Malone, 1979;Roux et al, 2008;Wiens et al [2008]), the failure across basal ice layers during the breaking off of hanging glaciers (Faillettaz et al, 2008), or changes in basal sliding due to changes in basal water pressures (Walter et al, 2008). Thus, icequakes occurring near the glacier bed should be a focus for future efforts of source parameter calculations.…”

Section: Resultsmentioning

confidence: 99%

Moment Tensor Inversions of Icequakes on Gornergletscher, Switzerland

Walter

Clinton²,

Deichmann³

et al. 2009

Bulletin of the Seismological Society of America

109

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We have determined seismic source mechanisms for shallow and intermediate-depth icequake clusters recorded on the glacier Gornergletscher, Switzerland, during the summers of 2004 and 2006. The selected seismic events are part of a large data set of over 80,000 seismic events acquired with a dense seismic network deployed in order to study the yearly rapid drainage of Gornersee lake, a nearby icemarginal lake. Using simple frequency and distance scaling and Green's functions for a homogeneous half-space, we calculated moment tensor solutions for icequakes with M w 1:5 using a full-waveform inversion method usually applied to moderate seismic events (M w > 4) recorded at local to regional distances (≈50-700 km). Inversions from typical shallow events are shown to represent tensile crack openings. This explains well the dominating Rayleigh waves and compressive first motions observed at all recording seismograms. As these characteristics can be observed in most icequake signals, we believe that the vast majority of icequakes recorded in the 2 yr is due to tensile faulting, most likely caused by surface crevasse openings. We also identified a shallow cluster with somewhat atypical waveforms in that they show less dominant Rayleigh waves and quadrantal radiation patterns of first motions. Their moment tensors are dominated by a large double-couple component, which is strong evidence for shear faulting. Although less than a dozen such icequakes have been identified, this is a substantial result as it shows that shear faulting in glacier ice is generally possible even in the absence of extreme flow changes such as during glacier surges. A third source of icequakes was located at 100 m depth. These sources can be represented by tensile crack openings. Because of the high-hydrostatic pressure within the ice at these depths, these events are most likely related to the presence of water lenses that reduce the effective stress to allow for tensile faulting.Online Material: Background information and results of moment tensor inversions.

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Section: Resultsmentioning

confidence: 99%

Moment Tensor Inversions of Icequakes on Gornergletscher, Switzerland

Walter

Clinton²,

Deichmann³

et al. 2009

Bulletin of the Seismological Society of America

109

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“…Striking qualitative analogies with those of the 2005 Weisshorn event (Faillettaz et al, 2008) can be highlighted.…”

Section: The 2014 Break-off Eventmentioning

confidence: 96%

“…Although the break-off event would necessarily occur earlier, this critical time represents the upper limit of the break-off timing. Moreover, an oscillating pattern superimposed on the power law acceleration of the surface displacements was evidenced prior to the 2005 Weisshorn event (Pralong et al, 2005;Faillettaz et al, 2008). This peculiar glacier dynamics was shown to be a log-periodic oscillating process superimposed on this acceleration (for appearance and interpretation see Pralong, 2006 andFaillettaz et al, 2015).…”

Section: Previous Findings On Cold Glacier Break-offmentioning

confidence: 99%

“…12d in Pralong and Funk, 2006). The maturation of the rupture was shown to be associated with a typical time evolution of both surface velocities (Faillettaz et al, 2008) and passive seismic activity (Faillettaz et al, 2011a). This characteristic time evolution can theoretically be used to predict the occurrence of a catastrophic event.…”

Section: Introductionmentioning

confidence: 99%

“…Because of the long distance between the theodolite and the reflectors, a small error in angle measurement has considerable impact on the accuracy of the calculated position. Following Faillettaz et al (2008), two corrections were applied to the raw data to improve the accuracy. First, the distance was corrected using two reference points located on the rock next to the glacier to compensate the meteorological disturbances of the air temperature, humidity and pressure.…”

Section: Previous Findings On Cold Glacier Break-offmentioning

confidence: 99%

See 2 more Smart Citations

Time forecast of a break-off event from a hanging glacier

Faillettaz¹,

Funk²,

Vagliasindi³

2016

The Cryosphere

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Abstract. A cold hanging glacier located on the south face of the Grandes Jorasses (Mont Blanc, Italy) broke off on the 23 and 29 September 2014 with a total estimated ice volume of 105 000 m 3 . Thanks to accurate surface displacement measurements taken up to the final break-off, this event was successfully predicted 10 days in advance, enabling local authorities to take the necessary safety measures. The breakoff event also confirmed that surface displacements experienced a power law acceleration along with superimposed log-periodic oscillations prior to the final rupture. This paper describes the methods used to achieve a satisfactory time forecast in real time and demonstrates, using a retrospective analysis, their potential for the development of early-warning systems in real time.

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Avalanching glacier instabilities: Review on processes and early warning perspectives

Faillettaz

Funk

Vincent

2015

Reviews of Geophysics

Self Cite

103

102

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Avalanching glacier instabilities are gravity-driven rupture phenomena that might cause major disasters, especially when they are at the origin of a chain of processes. Reliably forecasting such events combined with a timely evacuation of endangered inhabited areas often constitute the most efficient action. Recently, considerable efforts in monitoring, analyzing, and modeling such phenomena have led to significant advances in destabilization process understanding, improving early warning perspectives. The purpose of this paper is to review the recent progress in this domain. Three different types of instabilities can be identified depending on the thermal properties of the ice/bed interface. If cold (1), the maturation of the rupture is associated with a typical time evolution of surface velocities and passive seismic activity. A prediction of the final break off is possible using these precursory signs. For the two other types, water plays a key role in the development of the instability. If the ice/bed interface is partly temperate (2), the presence of meltwater may reduce the basal resistance, which promotes the instability. No clear and easily detectable precursory signs are known in this case, and the only way to infer any potential instability is to monitor the temporal evolution of the thermal regime. The last type of instability (3) concerns steep temperate glacier tongues switching for several days/weeks during the melting season into a so-called "active phase" followed in rare cases by a major break-off event. Although the prediction of such events is still far from being achievable, critical conditions promoting the final instability can be identified.

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Evidence of log-periodic oscillations and increasing icequake activity during the breaking-off of large ice masses

Cited by 45 publications

References 27 publications

Moment Tensor Inversions of Icequakes on Gornergletscher, Switzerland

Moment Tensor Inversions of Icequakes on Gornergletscher, Switzerland

Time forecast of a break-off event from a hanging glacier

Avalanching glacier instabilities: Review on processes and early warning perspectives

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