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Terre Univers Environnement

Seismic monitoring of a rocky glacier

toward understanding an emerging risk.

par Encadrants de stages - 20 octobre 2016

Title : Seismic monitoring of a rocky glacier : toward understanding an emerging risk.

Laboratory : ISTerre

Advisors : Agnès HELMSTETTER
Laurent BAILLET
Eric LAROSE

key words : Natural Hazards, seismic noise, micro-seismicity,

context and objectives of the internship :
Rocky glaciers are mountain areas where rocks and ice accumulate together in variable respective proportions. From the surface they look like rocky scree and there actual movement was detected only recently (after 1970’s for most of them). With global warming, the ice cementing the rocky landslide progressively vanishes and the slope destabilizes. This phenomenon is the basis of what we can call a new « merging » natural hazard that was inexistent or extremely rare some decades ago.

Within the partnership with the Valais geological service, the Research Center for Alpine Environment (CREALP), and the Environmental and Risk Geophysics team at ISTerre, we set an array of 6 seismic sensors on the Gugla Glacier above Zermatt (altitude ranging from 2700m to 3200m). The internship will consist in processing one year of seismic ambient noise and the micro-seismic activity. This dataset is unique in the world.

The goals of the internship are based on two strategies:1) analyzing the micro-seismicity ; 2) evaluate the relative seismic velocity changes form daily ambient noise cross-correlation. The questions to address are the following : Where are located the seismic events and do they help to better understand the mechanical deformation of the rocky glacier at depth ? Does a sliding layer exist ? Does the micro-seismic activity relate to surface deformation, including spring acceleration in connection to melting ? Do relative velocity changes connect to a rigidity reduction (internal ice melt) or to an increase in water content (increase of density) ? In the end, is it possible to use seismology as a precursor signal of slope destabilization/slope failure ?

requested skills : good knowledge in data processing, wave physics, geophysics, seismology, acoustics, and mechanics. Fieldwork skills are appreciated but not mandatory.

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