Abstract On 28th September 2018, an earthquake of Mw 7.5 hit the Central Sulawesi province in Indonesia. This was followed by liquefaction-induced large-scale ground flows in several areas in Palu city and its neighborhood. A significant characteristic of the ground flows at these sites was that large volume of soil slid downhill along gentle topographic gradients and travelled long distances (more than several hundred meters). To gain a better understanding of the fundamental mechanisms contributing to ground flows, this geo-disaster report summarizes a site investigation conducted at Sibalaya, one of the sites where massive ground flows were observed. We conducted interviews to reveal the time sequence of the event, including the main shaking that was followed by a sudden drop of the ground surface, the time at which the massive ground flow was initiated (with an extremely loud sound), as well as the change in the water level of wells. Water leakage from the unlined irrigation channel was confirmed to contribute significantly to the increase in the ground water level in this area, which thus increased the liquefaction potential. In situ tests, including eight large trench excavations and dynamic cone penetration tests, were carried out, which helped identify the liquefied and largely sheared layers. An analysis of the change in topography using satellite images and UAV photos also played an important role in capturing the overall picture of the event. Finally, a hypothesized mechanism for the extremely long slide was discussed.

中文翻译：

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2018 年苏拉威西地震导致锡巴拉亚的大规模水流滑坡

摘要 2018 年 9 月 28 日，印度尼西亚中苏拉威西省发生 7.5 级地震。随后在帕卢市及其附近的几个地区发生了液化引起的大规模地面流动。这些地点地流的一个显着特征是大量土壤沿着平缓的地形梯度滑下坡并长距离移动（超过数百米）。为了更好地了解导致地流的基本机制，这份地质灾害报告总结了在 Sibalaya 进行的现场调查，这是观察到大量地流的地点之一。我们进行了采访以揭示事件的时间顺序，包括主要的震动以及随后的地面突然下降，大量地流开始的时间（声音非常大），以及井水位的变化。无内衬灌溉渠道的漏水被证实显着增加了该地区地下水位，从而增加了液化潜力。进行了现场测试，包括八次大型沟槽开挖和动态锥体穿透测试，这有助于识别液化和大剪切层。使用卫星图像和无人机照片对地形变化的分析也在捕捉事件的整体画面方面发挥了重要作用。最后，讨论了超长滑梯的假设机制。无内衬灌溉渠道的漏水被证实显着增加了该地区地下水位，从而增加了液化潜力。进行了现场测试，包括八次大型沟槽开挖和动态锥体穿透测试，这有助于识别液化和大剪切层。使用卫星图像和无人机照片对地形变化的分析也在捕捉事件的整体画面方面发挥了重要作用。最后，讨论了超长滑梯的假设机制。无内衬灌溉渠道的漏水被证实对该地区地下水位的增加有显着贡献，从而增加了液化潜力。进行了现场测试，包括八次大型沟槽开挖和动态锥体穿透测试，这有助于识别液化和大剪切层。使用卫星图像和无人机照片对地形变化的分析也在捕捉事件的整体画面方面发挥了重要作用。最后，讨论了超长滑梯的假设机制。进行了包括 8 次大型沟渠开挖和动态锥体穿透测试，这有助于识别液化和大剪切层。使用卫星图像和无人机照片对地形变化的分析也在捕捉事件的整体画面方面发挥了重要作用。最后，讨论了超长滑梯的假设机制。进行了包括 8 次大型沟渠开挖和动态锥体穿透测试，这有助于识别液化和大剪切层。使用卫星图像和无人机照片对地形变化的分析也在捕捉事件的整体画面方面发挥了重要作用。最后，讨论了超长滑梯的假设机制。