Abstract After several months of eruptive activity, the subaerial cone of Anak Krakatau collapsed on December 22, 2018. The landslide event generated a tsunami that had deadly consequences within the Sunda Strait in Indonesia. Such significant collapse events are common in the geologic record but are a rare phenomenon, in the instrumented record. However, these events can have a potentially large impact on society. We have reconstructed the collapse, along with the activity preceding and following it, by combining information from official reports, remote geophysical observations, and local eyewitness accounts. It appears that the collapse of Anak Krakatau's subaerial cone led to a drastic change in the eruptive style from continuous Strombolian explosions to sustained Surtseyan. Those changes are detectable in the seismo-acoustic measurements, which, when combined with eyewitnesses, allows us to reconstruct the timing and phenomenology of the sequence. Our analysis reveals that intense eruptive activity generated sustained infrasound, unusual but not unique at Anak Krakatau, starting approximately eight hours before the collapse. Within this timeframe, two seismic signals consistent with minor mass movements as well as a momentary quiescence were identified prior to the main collapse. The data presented here indicate that Anak Krakatau failed in one collapse event, producing a tsunami with multiple waves around the volcano, the last one being the largest. Following the collapse, three volcanic plumes could be clearly identified in the satellite data and by eyewitnesses, as well as spectral lines in the seismic data. These lines, observed up to 371 km, suggest a repeating energetic explosive source lasting for seven days. The collapse produced multiple infrasound arrivals observed at regional infrasound stations, but was not recorded on the regional hydroacoustic network. Our analysis of the eruptive sequence demonstrates that a detailed eruption chronology can be reconstructed using remote methods, even in the event of failure or destruction of local monitoring infrastructure. This event also highlights that tsunamigenic flank collapses can occur with little to no warning, and be difficult to interpret in real-time, as a significant amount of non-operational analysis was required after the event, to complete the chronology.

中文翻译：

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根据目击者报告、地震声学和卫星观测，重建 2018 年在喀拉喀托发生的海啸坍塌和喷发活动

摘要 经过数月的喷发活动，喀拉喀托山下锥体于 2018 年 12 月 22 日坍塌。滑坡事件引发了海啸，对印度尼西亚巽他海峡造成了致命后果。这种重大的坍塌事件在地质记录中很常见，但在仪器记录中却是罕见的现象。然而，这些事件可能会对社会产生巨大的影响。我们通过结合官方报告、远程地球物理观测和当地目击者叙述的信息，重建了坍塌及其前后的活动。似乎 Anak Krakatau 的地面锥体的坍塌导致喷发风格从连续的 Strombolian 爆炸到持续的 Surtseyan 爆发发生了巨大变化。这些变化可以在地震声学测量中检测到，当与目击者结合时，我们可以重建序列的时间和现象学。我们的分析表明，在崩塌前大约 8 小时开始，强烈的喷发活动产生了持续的次声波，这在喀拉喀托阿纳克喀拉喀托地区不寻常但并非独一无二。在这个时间范围内，在主要坍塌之前确定了两个与轻微质量运动以及瞬间静止一致的地震信号。这里提供的数据表明 Anak Krakatau 在一次坍塌事件中失败，在火山周围产生了多波海啸，最后一个是最大的。坍塌后，卫星数据和目击者以及地震数据中的谱线可以清楚地识别出三个火山羽流。这些线，观察到长达 371 公里，建议持续 7 天的重复能量爆炸源。坍塌产生了在区域次声站观测到的多次次声到达，但没有记录在区域水声网络上。我们对喷发序列的分析表明，即使在本地监测基础设施出现故障或破坏的情况下，也可以使用远程方法重建详细的喷发年表。该事件还突出表明，海啸引起的侧翼坍塌可能在几乎没有警告的情况下发生，并且难以实时解释，因为在事件发生后需要进行大量的非操作性分析来完成年表。但没有记录在区域水声网络上。我们对喷发序列的分析表明，即使在本地监测基础设施出现故障或破坏的情况下，也可以使用远程方法重建详细的喷发年表。该事件还突出表明，海啸引起的侧翼坍塌可能在几乎没有警告的情况下发生，并且难以实时解释，因为在事件发生后需要进行大量的非操作性分析来完成年表。但没有记录在区域水声网络上。我们对喷发序列的分析表明，即使在本地监测基础设施出现故障或破坏的情况下，也可以使用远程方法重建详细的喷发年表。该事件还突出表明，海啸引起的侧翼坍塌可能在几乎没有警告的情况下发生，并且难以实时解释，因为在事件发生后需要进行大量的非操作性分析来完成年表。