NERC Urgency Sulawesi tsunami 2018

当地时间2018年9月28日下午6点，印度尼西亚苏拉威西岛西部发生了一次走滑地震，震级为Mw 7.5。地震震动立即摧毁了帕卢市的大片地区，帕卢市是最近的一个拥有135，000人口的大城镇。进一步的破坏是由下面的细粒河流沉积物液化造成的，这些沉积物引发了席卷整个城市的泥石流。地震后不久，高达11米的海啸淹没了当地海岸线，造成进一步的破坏，特别是对帕卢市和更北部的东加尔。目前，已知有2,100人在这起事件中死亡，700多人失踪。最近的海啸提供了有关机制和影响的重要信息，为通报灾害和风险提供了必要的数据。苏拉威西地震的机制是重要的，因为它不同于最近的破坏性事件，如巴布亚新几内亚（1998年），印度洋（2004年）和日本（2011年），这些事件是由逆冲断层触发的。苏拉威西是一个以水平运动为主的走滑断裂。目前对地震海啸生成的理解表明，由于没有显著的垂直海底海拔，它不应该产生有记录的海啸（高达11米）。初步的海啸数值模拟证实了这一认识。需要一个额外的海啸机制，海底滑坡是最有可能的。海啸的数值模拟需要通过实地观测进行验证，以确认其准确性。这些观测必须在海啸发生后尽快进行，因为有关海啸及其规模的许多证据都极其脆弱和短暂。例如，水流的方向可以通过压平的草来确定;海啸水流的深度和高度可以通过建筑物上的水痕或建筑物损坏、植被剥离和树木或灌木丛中的碎片来确定。沉积的沉积物，特别是在季风条件下，很快被侵蚀或移走。因此，在发生大海啸后，必须尽快进行实地观察和研究。在这里，对于苏拉威西岛，我们提出了一个紧急响应现场调查，调查前的解释之前和之后的高分辨率卫星图像的基础上。研究结果将详细确定海啸淹没的地理变化，这将为海啸的影响、潜在的海啸机制提供信息，并为海啸数值模型提供验证。这一方法（案头研究后开展实地工作）已成功应用于2011年日本海啸，是朝着开发一个可互操作的数字实地数据收集综合系统迈出的关键第一步。从目前的实地调查中可以了解到大部分但不是全部受海啸影响地区的情况（见2）。近海走滑破裂（由遥感干涉合成孔径雷达数据绘制）和洪水测量的海啸现场证据之间存在密切的相关性。近海破裂和海岸沉降之间也存在相关性，这支持海岸/海底滑坡作为海啸机制。对于拟议的调查，PI Tappin领导了一项国际和多学科倡议（英国，印度尼西亚，美国和波兰），以研究苏拉威西海啸。这种方法最有可能充分了解这一事件，也是必要的，因为目前印度尼西亚的海啸预警是基于远场地震。当地触发的事件，如苏拉威西岛，警报最低，目前没有得到处理。更广泛地说，该项目将有助于更好地了解当地的，走滑触发，海底滑坡海啸及其危害。该项目将为这方面改进的缓解战略提供信息。这项研究将为今后更深入的研究奠定基础。

At 6pm local time on the September 28th 2018, a strike-slip earthquake, Mw 7.5, struck the west of Sulawesi Island in Indonesia. Earthquake shaking immediately destroyed large areas of Palu City, the nearest large town of 135,000 people. Further damage was caused by liquefaction of underlying, fine-grained fluvial sediments, which mobilised mudslides that swept through the city. Soon after the earthquake, tsunamis, with elevations of up to 11 m inundated local coastlines causing further destruction, especially to Palu City, and Donggal farther north. At present, 2,100 people are known to have died in the event with over 700 missing. A significant number of these died in the tsunamis.Recent tsunamis provide critical information on mechanisms and impacts which provide essential data on informing on hazard and risk. The mechanism of the Sulawesi earthquake is significant because it is different to recent devastating events, such as Papua New Guinea (1998), Indian Ocean (2004) and Japan (2011), which were triggered by thrust faulting. Sulawesi is a strike-slip rupture with dominantly horizontal movement. Present understanding of earthquake tsunami generation suggests that, because of the absence of significant vertical seabed elevation, it should not have generated the recorded (up to 11m) tsunamis. Preliminary numerical tsunami modelling confirms this understanding. An additional tsunami mechanism is required, and submarine landslides are most likely. Numerical modelling of tsunamis require validation from field observations to confirm their accuracy. These observations have to be made as soon as possible after impact because much of the evidence on the tsunami and its' scale is extremely fragile and short-lived. For example, the directions of flow may be identified by flattened grass; tsunami flow depth and elevation may be identified from water marks on buildings or building damage, vegetation stripping and debris caught in trees or bushes. Sediment deposited, especially in monsoonal conditions, is rapidly eroded or removed. It is vital therefore that after a major tsunami, field observations are made and the research carried out as soon as practicable. Here, for Sulawesi, we propose an urgent response field survey, based on pre-survey interpretations of before and after high-resolution satellite imagery. The results will identify in detail geographical variations on tsunami inundation which will inform on the impact, potential tsunami mechanisms and offer validation for numerical tsunami models. This methodology (desk study followed by field work) was successfully applied to the Japan 2011 tsunami, and is a first critical step towards developing an integrated system for interoperable digital field data collection. From the present field surveys there is information over much, but not all, of the area impacted by the tsunami (see 2). There is a close correlation between the offshore strike-slip rupture (mapped from remote - inSAR data) and field evidence for a tsunami from inundation measurements. There is also correlation between the offshore rupture and coastal subsidence, which supports coastal/submarine landslides as the tsunami mechanism. For the proposed survey, PI Tappin leads an international and multidisciplinary initiative (UK, Indonesia, US and Poland) to study the Sulawesi tsunami. This approach is most likely to fully understand the event, and is required because, at present tsunami warning in Indonesia is based on far-field earthquakes. Locally triggered events, such as Sulawesi, where there was minimal warning, are not at present addressed. More broadly, the project will contribute to an improved understanding of locally, strike-slip triggered, submarine landslide tsunamis and their hazard. The project will inform on improved mitigation strategies in this context. The research will form the basis for future, more in depth research.