Investigating Brittle Fracture during Viscous Creep at the Super-Sauze Mudslide by a Comprehensive Field Laboratory

Applying Nanoseimic Monitoring by seismic small-arrays at the soft rock Super-Sauze mudslide in the French Alps, we observed fracture processes of slope material, also called slidequakes. The time-frequency signature of these events resembles the impulsive signals from local earthquakes by brittle fracture of Earth crust. We could locate the slidequakes up to some hundred m off the arrays, and determine ML between –3 and –1. However, due to the very poor SNR neither precise depths nor moment tensors could be derived. Thus seismological tools alone will not answer the open questions on source mechanism, and how these fractures relate to slope movement. We decided to conduct additional geophysical mapping complemented by high-resolution aerial reconnaissance. The field laboratory was established for eight weeks at a prominent spot of Super-Sauze where mudslide channeling by in-situ crests caused many slidequakes. Besides slidequakes, we observed another type of signal resembling ETS which might be related to scratch of embedded rocks creeping along the in-situ crests, and coincided with fissure opening at surface. Additional monitoring of slope movement, pore water pressure build-up, and soil moisture will help to relate our observations to spatial-temporal variation of material properties.