Slidequake Generation versus Viscous Creep at Softrock-landslides: Synopsis of Three Different Scenarios at Slumgullion Landslide, Heumoes Slope, and Super-Sauze Mudslide

In this study, we describe conditions for slidequake generation at three different creeping softrock landslides: the Slumgullion landslide in the San Juan Mountains, Colorado, U.S., the Heumoes slope in the Austrian Alps, and the mudslide in Super-Sauze, French Alps. From a geomorphologic point of view, all three landslides are classified as creeping landslides with average velocities between centimeters to meters per year. Associating creep with viscous flow, and considering the largely saturated, clayey consistency of the slope body, one would not expect any brittle behavior. Thus, it came as a surprise that impulsive seismic signals indicative of shear fracture could be discovered by sensitive passive monitoring methods at all three slopes. These fracture signals occur in episodes, have similar signatures as small earthquakes, and could be located within the slide bodies, Le., are evidence of slidequakes. Our investigations identified seismic and aseismic slip in each slide, with slidequakes focusing at significant bedrock structures or at lateral boundaries. Synoptic comparison of three scenarios underlines the importance of landslide-bedrock and landslide-lateral boundary interactions under gravitational loading and Mohr-Coulomb-type failure. Comparison to frictional and asperity models of crustal- and plate-scale boundaries may pave the way to a comprehensive understanding of slidequake generation, and future slope failure prediction.