Seismic measurement of the propagation speed of a fracture through a weak snowpack layer

Ben Johnson, Bruce Jamieson, Robert R. Stewart

Weak layers in the snowpack can fail, often resulting in a snow fracture and possibly resulting in an avalanche. Occasionally, these weak layer fractures are triggered on horizontal terrain and propagate into steep terrain to release an avalanche. Avalanches released in this type of manner are considered remotely triggered avalanches. A new field technique has been developed using geophones to measure the speed of a propagating fracture through horizontal terrain. We used six geophones placed approximately 5 m apart and artificially triggered a fracture in a weaker layer. During the winter of 1999/2000, a fracture was measured propagating at 19.9 m/s.