Seismic measurement of fracture speed in a weak snowpack layer

• Published in: Cold regions science and technology Vol. 40; no. 1; pp. 41 - 45
• Main Authors: Johnson, B.Crane, Jamieson, J.Bruce, Stewart, Robert R.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-11-2004
• Subjects: Fracture propagation; Fracture speed; Snowpack stratigraphy; Snowpack stratigraphy; Fracture speed; Fracture propagation
• ISSN: 0165-232X; 1872-7441
• DOI: 10.1016/j.coldregions.2004.05.003

Fractures in weak layers of a snowpack can propagate over distances ranging from meters to kilometers. Occasionally, these weak layer fractures are triggered on low-angled terrain and propagate into steep terrain to release an avalanche. Avalanches released in this way are considered remotely triggered avalanches. This paper describes a new field technique that uses geophones (velocity motion sensors) to measure the speed of a fracture propagating in a weak layer through a horizontal snowpack. In February 2000, six geophones were placed approximately 5 m apart along a transect on the surface of the snow. A fracture in a 10-mm-thick weak snowpack layer was artificially triggered and the motion of the snow surface indicates a propagation speed of 20 m s
−1. The detected flexural wave in the slab supports a recent theory for fracture propagation due to collapse in a weak snowpack layer across horizontal terrain.