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Abstract: A hanging glacier at the east face of Weisshorn Switzerland broke off in2005. We were able to monitor and measure surface motion and icequake activityfor 25 days up to three days prior to the break-off. The analysis of seismicwaves generated by the glacier during the rupture maturation process revealedfour types of precursory signals of the imminent catastrophic rupture: i anincrease in seismic activity within the glacier, ii a decrease in the waitingtime between two successive icequakes, iii a change in the size-frequencydistribution of icequake energy, and iv a modification in the structure ofthe waiting time distributions between two successive icequakes. Morevover, itwas possible to demonstrate the existence of a correlation between the seismicactivity and the log-periodic oscillations of the surface velocitiessuperimposed on the global acceleration of the glacier during the rupturematuration. Analysis of the seismic activity led us to the identification oftwo regimes: a stable phase with diffuse damage, and an unstable and dangerousphase characterized by a hierarchical cascade of rupture instabilities wherelarge icequakes are triggered.



Autor: Jerome Faillettaz, Didier Sornette, Martin Funk

Fuente: https://arxiv.org/







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