  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.
