Seismic Monitoring of Slope Dynamics Caused by a Slow-moving Landslide in the Vorarlberg Alps, Austria

Our work within the research unit ‘Natural Slopes’ is mainly focused on the monitoring of seismic signals caused by the movement of the Heumoes slope in the Vorarlberg Alps, Austria. The slope is set up by weak sediments and moves with several cm per year at the surface. During several field campaigns within the last three years we were able to detect and locate single fracture processes during the movement of the Heumoes slope by applying the method Nanoseismic Monitoring (Joswig, 2008) to the Heumoes slope. Dozens of fractures with magnitudes varying between -0.7 ≤ ML ≤ -2.4 have been detected and located. The spatial distribution of the epicentres correlates with slope areas of higher movement rates. The temporal occurrence of the detected fractures, up to 26 hours after intense rain events, seems to approve the assumption of a rainfall-triggered movement of the slope caused by fast subsurface water dynamics. The epicenters are mainly clustered in the western part of the slope, where the water saturation of the material varies with the season. We therefore preliminary assume, that the recorded fractures have been generated in dependence of the water saturation of the unstable sediments.