Aletschgletscher

The study of small earthquakes related to glacier flow, so-called icequakes, can reveal important insights into the dynamics and hydraulics of glaciers. Icequakes near the glacier bed are particularly interesting, because they may be a manifestation of microseismic stick-slip sliding. This phenomenon is not fully understood and has yet to be captured in ice flow models. At the same time, basal seismicity can be a manifestation of hydraulic fracturing as melt water opens up new water channels within and beneath the glacier, a process, which is analogous to the hydraulic stimulation within geothermal reservoirs.

This project focuses on the occurrence of sliding-related stick-slip icequakes beneath Aletschgletscher. Whereas these events have been confirmed beneath the polar ice sheets (e.g. Smith et al., 2015; Roeoesli et al., 2016), it is to date not clear if they also exist beneath relatively flat Alpine glaciers. To this end, the SED conducted a two-step seismometer deployment on the glacier tongue. In a first step, three shallow borehole seismometers were installed and maintained for 1.5 years (January 2015-July 2016). These data identified an icequake cluster at the glacier bed, which was monitored in near-real time with the help of state-of-the-art real-time data communication. In June 2016, an additional network with six seismometers was installed above the cluster to confirm that the recorded icequakes are indeed stick-slip events and to provide better hypocenter locations.

The seismic Aletschgletscher record is unique in that it contains stick-slip icequakes recorded at an unrivaled quality over more than a year. This will provide an unprecedented look at seismogenic stick-slip sliding and its changes over the course of a full year. As a result of harsh weather conditions in high-melt areas, on-ice seismometer installations are extremely difficult on Alpine glaciers. Consequently, the Aletschgletscher data set offers a first-of-its-kind view on how stick-slip seismicity changes as the glacier reacts to climatic changes.

Our project is embedded in cross-disciplinary collaborative research between the Glaciology division at the Laboratory of Hydraulics, Hydrology, and Glaciology (VAW) at ETH Zurich and the Exploration and Environmental Geophysics group at the Institute of Geophysics at ETH Zurich. In the past, these groups have collected milestone records in the field of glacier seismology (Podolskiy and Walter, 2016). The joint interpretation of the Aletschgletscher data will help to improve our understanding of glacier flow and its reaction to climate change and glacier retreat, also affecting the Swiss Alps.