Studies on Thermally Induced Fractures and Snowquakes of Polar Snow Cover

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Thermally induced fractures or thermal cracks, and pronounced seismic events as snowquakes were studied at Mizuho Station, East Antarctica from June 1976 to January 1977. Fractures due to thermal stress were found in the uppermost 50 cm of the snow cover as a result of snow temperature decrease at the surface, and fracture under tensile thermal stress occurs when the stress exceeds the tensile strength of snow. Once thermal cracks are initiated, stress concentration occurs at tips of cracks, and fractures occur more easily in the smaller thermal stress than the tensile strength of snow and accompany more easily pronounced seismic events, that is, snowquake. Snowquakes occur during the decrease of temperature and then thermally induced strain rate corresponds to ductile fracture of snow. The individual snowquakes occur in the near surface and the epicenters of snowquakes located by seismic observations are found near thermal cracks, which indicates that snowquake is caused by the formation of cracks. The epicenters are not distributed in a well-ordered sequence, thus the fractures of snow cover occur at random in the near surface which is under the tensile stress during the decrease of snow temperature.
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