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.

雪板雪崩以明显、宽阔的断裂线为特征，在埋藏在粘性板下方的高度多孔的薄弱雪层中随着反裂缝传播而释放。抗裂机制是由弱层的体积坍塌驱动的，这导致裂纹面的闭合和摩擦接触的开始。在这里，在雪断裂实验、全面雪崩测量和数值模拟的基础上，我们报告了从亚瑞利反裂纹到超剪切裂纹扩展的过渡的存在。这种转变遵循 Burridge-Andrews 机制，其中超剪切子裂纹在主裂缝前沿之前成核，并最终以比剪切波速度更快的速度传播。此外，我们表明，即使由于倒塌过程中摩擦阻力的损失，剪切与法向应力的比率低于静摩擦系数，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具有根本的相似性。