NERC Urgency Sulawesi tsunami 2018

当地时间2018年9月28日下午6时，印度尼西亚苏拉威西岛以西发生7.5级走滑地震。地震震动立即摧毁了帕鲁市的大片地区，帕鲁市是距离最近的13.5万人的大镇。进一步的破坏是由底层细粒河流沉积物的液化造成的，这引发了席卷全市的泥石流。地震发生后不久，海拔高达11米的海啸淹没了当地的海岸线，造成了进一步的破坏，特别是对帕卢市和更靠北的东加尔。目前，已有2100人在这起事件中死亡，700多人失踪。最近的海啸提供了关于机制和影响的重要信息，为通报灾害和风险提供了基本数据。苏拉威西地震的机制意义重大，因为它不同于最近发生的破坏性事件，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引发的。苏拉威西是一个以水平运动为主的走滑断裂。目前对地震海啸产生的理解表明，由于没有显著的海床垂直高度，它不应该产生记录在案的(最多11米)海啸。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，最有可能的是海底山体滑坡。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。这些观察结果必须在海啸发生后尽快做出，因为关于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识别；海啸的深度和高度可以通过建筑物上的水痕或建筑物损坏、植被剥落和树木或灌木丛中捕获的碎片来识别。沉积的沉积物，特别是在季风条件下沉积的沉积物，会迅速被侵蚀或清除。因此，至关重要的是，在发生重大海啸后，应尽快进行实地观察和研究。在这里，对于苏拉威西，我们建议进行一次紧急响应实地调查，基于调查前对高分辨率卫星图像前后的解释。结果将详细确定海啸淹没的地理变化，这将提供有关影响、潜在海啸机制的信息，并为数值海啸模型提供验证。这一方法(先进行案头研究，然后进行实地工作)被成功地应用于2011年日本海啸，这是朝着开发可互操作的数字实地数据收集综合系统迈出的关键的第一步。从目前的实地调查中，有关于受海啸影响的大部分地区的信息(见2)。近海走滑破裂(从遥感干涉合成孔径雷达数据绘制的地图)与淹没测量的海啸现场证据之间存在密切的相关性。近海破裂与海岸下沉之间也存在相关性，支持海岸/海底滑坡作为海啸机制。在拟议的调查中，Pi Tappin领导了一个国际和多学科倡议(英国、印度尼西亚、美国和波兰)来研究苏拉威西海啸。这种方法最有可能完全了解这一事件，而且是必要的，因为目前印度尼西亚的海啸预警是基于远场地震。当地引发的事件，如苏拉威西，在那里只发出了最低限度的警告，目前没有得到解决。更广泛地说，该项目将有助于更好地了解当地由走滑引发的海底山体滑坡海啸及其危害。该项目将在这方面通报改进的缓解战略。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.