Icequakes as precursors of ice avalanches

TL;DR

This study monitored seismic activity of a hanging glacier over 21 days, identifying precursors such as increased seismic activity, energy distribution changes, and oscillating patterns that signal an imminent ice avalanche.

Contribution

It presents a novel analysis of icequake signals as early indicators of glacier rupture, highlighting specific seismic precursors and regimes leading to avalanches.

Findings

Seismic activity increases before rupture.

Energy distribution shifts prior to failure.

Oscillating seismic patterns indicate unstable regimes.

Abstract

A hanging glacier at the east face of Weisshorn broke off in 2005. We were able to monitor and measure surface motion and icequake activity for 21 days up to three days prior to the break-off. Results are presented from the analysis of seismic waves generated by the glacier during the rupture maturation process. Three types of precursory signals of the imminent catastrophic rupture were identified: (i) an increasing seismic activity within the glacier, (ii) a change in the size-frequency distribution of icequake energy, and (iii) a log-periodic oscillating behavior superimposed on power law acceleration of the inverse of waiting time between two icequakes. The analysis of the seismic activity gave indications of the rupture process and led to the identification of two regimes: a stable one where events are isolated and non correlated which is characteristic of diffuse damage, and an unstable and dangerous one in which events become synchronized and large icequakes are triggered.