Trottet Bertil, Simenhois Ron, Bobillier Gregoire, Bergfeld Bastian, van Herwijnen Alec, Jiang Chenfanfu, Gaume Johan
École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
Colorado Avalanche Information Center, Boulder, CO USA.
Nat Phys. 2022;18(9):1094-1098. doi: 10.1038/s41567-022-01662-4. Epub 2022 Jul 25.
Snow slab avalanches, characterized by a distinct, broad fracture line, are released following anticrack propagation in highly porous weak snow layers buried below cohesive slabs. The anticrack mechanism is driven by the volumetric collapse of the weak layer, which leads to the closure of crack faces and to the onset of frictional contact. Here, on the basis of snow fracture experiments, full-scale avalanche measurements and numerical simulations, we report the existence of a transition from sub-Rayleigh anticrack to supershear crack propagation. This transition follows the Burridge-Andrews mechanism, in which a supershear daughter crack nucleates ahead of the main fracture front and eventually propagates faster than the shear wave speed. Furthermore, we show that the supershear propagation regime can exist even if the shear-to-normal stress ratio is lower than the static friction coefficient as a result of the loss of frictional resistance during collapse. This finding shows that snow slab avalanches have fundamental similarities with strike-slip earthquakes.
雪板雪崩的特征是有一条明显、宽阔的裂缝线，它是在埋于粘性雪板下方的高度多孔弱雪层中反裂纹扩展后发生的。反裂纹机制是由弱层的体积坍塌驱动的，这会导致裂纹面闭合并引发摩擦接触。在此，基于雪断裂实验、全尺寸雪崩测量和数值模拟，我们报告了从亚瑞利反裂纹到超剪切裂纹扩展的转变的存在。这种转变遵循伯里奇 - 安德鲁斯机制，即超剪切子裂纹在主断裂前沿之前成核，并最终以高于剪切波速度的速度传播。此外，我们表明，由于坍塌过程中摩擦阻力的丧失，即使剪应力与正应力之比低于静摩擦系数，超剪切传播状态也可能存在。这一发现表明雪板雪崩与走滑地震有基本的相似之处。
