Icequakes coupled with surface displacements for predicting glacier break-off

TL;DR

This study monitored surface displacements and icequake activity over 25 days to identify precursory signals indicating an imminent glacier break-off, revealing specific seismic patterns and a correlation with surface velocity oscillations.

Contribution

It introduces a detailed analysis of seismic precursors and surface displacement signals as predictors of glacier rupture, demonstrating their potential for early warning systems.

Findings

Increased seismic activity precedes break-off.

Decreased waiting times between icequakes signal instability.

Correlation between seismic activity and surface velocity oscillations.

Abstract

A hanging glacier at the east face of Weisshorn (Switzerland) broke off in 2005. We were able to monitor and measure surface motion and icequake activity for 25 days up to three days prior to the break-off. The analysis of seismic waves generated by the glacier during the rupture maturation process revealed four types of precursory signals of the imminent catastrophic rupture: (i) an increase in seismic activity within the glacier, (ii) a decrease in the waiting time between two successive icequakes, (iii) a change in the size-frequency distribution of icequake energy, and (iv) a modification in the structure of the waiting time distributions between two successive icequakes. Morevover, it was possible to demonstrate the existence of a correlation between the seismic activity and the log-periodic oscillations of the surface velocities superimposed on the global acceleration of the glacier during the rupture maturation. Analysis of the seismic activity led us to the identification of two regimes: a stable phase with diffuse damage, and an unstable and dangerous phase characterized by a hierarchical cascade of rupture instabilities where large icequakes are triggered.