The United States witnessed its deadliest landslide on March 22, 2014 in Oso, Washington. Forty-three people were killed and the direct financial damage exceeded 170 million dollars. The topography of the slope prior to this landslide was complex due to the occurrence of several historical landslides on the same slope and three-dimensional (3D) features of the slope. This paper utilizes an inverse 3D limit equilibrium analysis to propose a 3D failure mechanism and sequence for the 2014 Oso Landslide. The 3D mechanism consists of two main phases (Phase I and II) with three retrogressive slides that were identified during field reconnaissance and confirmed via the 3D limit equilibrium slope stability analyses. The 3D analysis suggests that Phase II of the Stark et al. (2017) mechanism consists of two separate retrogressive slides instead of a single slide. The two slides of Phase II are referred to as Phase IIa and Phase IIb herein for comparison with Stark et al. (2017). Photographs herein show the geometry and runout of Phases IIa and IIb. After Phase IIa, sloughing of the steep scarp in the upper plateau onto the Phase IIb slide mass continued for months. The 3D analysis includes the complexities of the ancient landslide bench along with surrounding slope geometry and features, which help explain the initiation and direction of slide movement.

美国于2014年3月22日在华盛顿的奥索目睹了最致命的山体滑坡。造成43人死亡，直接经济损失超过1.7亿美元。该滑坡之前的斜坡地形非常复杂，原因是同一斜坡上发生了几处历史滑坡，并且具有该斜坡的三维（3D）特征。本文利用逆3D极限平衡分析为2014年Oso滑坡提出了3D破坏机理和序列。3D机制由两个主要阶段（第一阶段和第二阶段）组成，三个阶段分别是在野外侦察过程中确定并通过3D极限平衡边坡稳定性分析确定的。3D分析表明，Stark等人的第二阶段。（2017）机制由两个独立的递归幻灯片组成，而不是由单个幻灯片组成。为了与Stark等人进行比较，在本文中将阶段II的两个玻片称为阶段IIa和阶段IIb。（2017）。本文中的照片显示了相IIa和相IIb的几何形状和跳动。在阶段IIa之后，高原上陡峭的陡崖向阶段IIb滑动块的塌陷持续了几个月。3D分析包括古代滑坡台的复杂性以及周围的斜坡几何形状和特征，这有助于解释滑坡运动的产生和方向。高原上陡峭的陡崖向IIb期滑坡体的塌陷持续了数月之久。3D分析包括古代滑坡台的复杂性以及周围的斜坡几何形状和特征，这有助于解释滑坡运动的产生和方向。高原上陡峭的陡崖向IIb期滑坡体的塌陷持续了数月之久。3D分析包括古代滑坡台的复杂性以及周围的斜坡几何形状和特征，这有助于解释滑坡运动的产生和方向。