Sediment signatures of the 2010 Chile Mw 8.8 earthquake

大地震（8级及以上）和相关的海啸是在地球构造板块碰撞的地方产生的，对震区和邻近海域人口稠密的海岸线都造成了重大危害。2010年2月27日，智利中部发生8.8级地震。这是有史以来第五或第六大地震，造成500多人死亡，50万所房屋严重受损，初步估计经济损失在150亿至300亿美元之间。我们寻求紧急资金，以便对海岸陆地隆起和下沉的沉积记录进行快速实地评估。我们将收集海啸沉积的沉积物和后来由每日潮汐沉积的沉积物。对这些沉积物的实验室分析将首次提供现代地质记录，用于调查这些大地震的长期记录，不仅在智利，而且在类似构造环境下的海岸，如阿拉斯加、华盛顿、俄勒冈、不列颠哥伦比亚省、日本、印度尼西亚和汤加。评估太平洋和印度洋周围未来的地震和海啸风险需要知道大地震发生的频率，间隔时间以及不同事件中陆地运动的模式如何变化。我们只能从近5000年的沉积物积累的地质调查中获得长期的模式。陆地和海平面的运动，以及海岸沉积（和恢复/重建工作）意味着地震后的现场观测对我们的古地震重建至关重要。这一点最近在印度洋海啸后的当代采样中得到了证明，但这发生在与智利明显不同的海岸和气候条件下。对智利沉积物的分析将帮助我们验证所使用的方法，并适用于所有这些其他地区。这些结果将有助于验证以下方法的有效性：(1)估算过去几千年来这些地区以前地震的隆起和沉降量；(2)确定每次大地震受抬升或下沉影响的区域，(3)确定每次是否有类似大小的区域破裂，或者当构造板块边界的两个相邻部分同时破裂时，我们是否会发生更大的地震。紧迫感有三个关键原因。首先，随着智利的恢复，我们预计随着农田的恢复和潮间带盐沼放牧的恢复，原始沉积物将会减少。其次，中等规模海啸的沉积物痕迹往往是短暂的，在那里，上升延伸到潮上带。大雨在智利的这个地区很常见，可能会在几个月内摧毁海啸的沉积证据。第三，断裂带南端的地点可能会保留1960年智利地震（9.5级，仪器记录的最大地震）证据的重叠、混合或分离，因为这些地点位于间隔50年可能记录两次地震的地区。这将为分离几千年来保存在沉积记录中的多段和单段大地震的测试方法和模型提供独特的沉积证据。在评估地震危险、海啸产生和构造板块碰撞边界的长期发展方面，这是一个关键的争论。

Great earthquakes (Magnitude 8 and above) and related tsunami, generated where the Earth's tectonic plates collide, produce major hazards for both the earthquake area and heavily populated coastlines across much of the adjacent ocean. On 27th February 2010, a Mw 8.8 earthquake struck central Chile. This is the 5th or 6th largest earthquake ever recorded and resulted in over 500 deaths, with 500,000 homes significantly damaged and initial estimates of the financial cost ranging from $15bn to $30bn. We seek urgency funding to make a rapid field assessment of the sedimentary record of land uplift and subsidence at the coast. We shall collect sediments deposited by the tsunami and those deposited later by daily tides. Laboratory analyses of these sediments will provide, for the first time, the modern equivalent of geological records used to investigate the long-term record of these large earthquakes, not just in Chile but coasts in similar tectonic settings, e.g. Alaska, Washington, Oregon, British Columbia, Japan, Indonesia and Tonga. Evaluating future earthquake and tsunami risk around the Pacific and Indian Oceans requires knowing how frequently great earthquakes occur, at what intervals and how the patterns of land movement vary in different events. We can only obtain the long term patterns from the geological investigations of sediments accumulating of the last 5000 years. Land and sea-level motions, as well as coastal sedimentation (and restoration / reconstruction efforts) mean that field observations from the immediate post earthquake event are critical to our palaeoseismic reconstructions. This has been recently shown in the contemporary sampling that followed the Indian Ocean tsunami but this took place in a markedly different coastal and climate regime to that in Chile. Analysis of the sediments from Chile will help us to validate methods used and applicable to all these other areas. The results will help validate methods to (1) estimate the amount of uplift and subsidence in previous earthquakes over the past few thousand years in these areas; (2) determine the area affected by uplift or subsidence in each great earthquake, and (3) determine whether similar sized areas rupture each time, or can we have even greater earthquakes when two adjacent parts of the tectonic plate boundaries rupture at the same time. There are three key reasons for urgency. First, as restoration takes place in Chile we expect to see the loss of pristine sediments as farmland is recovered and grazing resumes on intertidal salt marshes. Second, sediment traces of medium sized tsunami are often ephemeral, where the run-up extends into the supratidal zone. Heavy rainfall, which is common in this area of Chile, will likely destroy sedimentary evidence of the tsunami within a few months. Third, sites at the southern end of the rupture will potentially preserve the overlap, mixing or separation of evidence of the 1960 Chile earthquake (Magnitude 9.5, the largest ever recorded by instrumentation) as these sites lie in the area potentially recording two earthquakes 50 yr apart. This will provide unique sedimentary evidence for testing methods and models for separating multi-segment from single-segment great earthquakes preserved in the sedimentary record for the last few thousand years. This is a critical debate in assessing earthquake hazard, tsunami generation and the long-term development of the boundaries where tectonic plates collide.