Abstract The 2018 MW 7.5 Palu-Donggala, Indonesia earthquake initiated a series of catastrophic flowslides that claimed the lives of several thousand people, making it the deadliest natural disaster of 2018. Three of the most significant flowslides, which occurred in the communities of Petobo, Jono Oge, and Lolu Village, were clustered within alluvial sediments of the Palu River Valley. Post-earthquake field reconnaissance, subsurface investigation, eyewitness interviews, and geomechanical analyses indicate that the failure sequence began when the earthquake ground motion raised pore water pressures in the saturated interbedded alluvial sediments. The flowslides were not coseismic but instead occurred several minutes after earthquake shaking ended. We hypothesize that high excess pore pressures created large hydraulic gradients within the alluvial sediments, which ultimately triggered progressive liquefaction that led to a redistribution of stresses and accumulation of shear strains. The flowslides were then initiated as gravitational driving stresses began to exceed the residual strength of the liquefied soil. Given the interbedded stratigraphy, we speculate that void redistribution and the development of water films possibly contributed to low residual strengths. An adjacent unlined agricultural canal played a critical role in the failure sequence by artificially raising the groundwater level, thereby increasing the susceptibility to liquefaction and attendant strength loss.

中文翻译：

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2018 年 M 7.5 帕卢-东加拉地震引发的东帕卢河谷水流滑坡

摘要 2018 年 7.5 兆瓦的印度尼西亚帕卢-东加拉地震引发了一系列灾难性水流滑坡，夺走了数千人的生命，使其成为 2018 年最致命的自然灾害。发生在 Petobo 社区的三起最严重的水流滑坡， Jono Oge 和 Lolu Village 聚集在帕卢河流域的冲积沉积物中。震后实地勘察、地下调查、目击者访谈和地质力学分析表明，当地震地面运动提高饱和互层冲积沉积物中的孔隙水压力时，破坏序列就开始了。流滑坡不是同震的，而是在地震结束后几分钟发生的。我们假设高超孔隙压力在冲积沉积物中产生了大的水力梯度，最终引发了逐渐液化，导致应力重新分布和剪切应变的积累。当重力驱动应力开始超过液化土壤的残余强度时，流动滑坡就开始了。鉴于互层地层，我们推测空隙重新分布和水膜的发展可能导致低残余强度。相邻的无衬里农业运河通过人为地提高地下水位在失败序列中发挥了关键作用，从而增加了液化的敏感性和随之而来的强度损失。最终引发逐渐液化，导致应力重新分布和剪切应变的积累。当重力驱动应力开始超过液化土壤的残余强度时，流动滑坡就开始了。鉴于互层地层，我们推测空隙重新分布和水膜的发展可能导致低残余强度。相邻的无衬里农业运河通过人为地提高地下水位在失败序列中发挥了关键作用，从而增加了液化的敏感性和随之而来的强度损失。最终引发逐渐液化，导致应力重新分布和剪切应变的积累。当重力驱动应力开始超过液化土壤的残余强度时，流动滑坡就开始了。鉴于互层地层，我们推测空隙重新分布和水膜的发展可能导致低残余强度。相邻的无衬里农业运河通过人为地提高地下水位在失败序列中发挥了关键作用，从而增加了液化的敏感性和随之而来的强度损失。我们推测空隙的重新分布和水膜的形成可能导致残余强度低。相邻的无衬里农业运河通过人为地提高地下水位在失败序列中发挥了关键作用，从而增加了液化的敏感性和随之而来的强度损失。我们推测空隙的重新分布和水膜的形成可能导致残余强度低。相邻的无衬里农业运河通过人为地提高地下水位在失败序列中发挥了关键作用，从而增加了液化的敏感性和随之而来的强度损失。