Collaborative Research: Deep imaging of the south-central Chile margin to understand plate boundary development and its control on megathrust slip behavior

合作研究：智利中南部边缘深度成像，以了解板块边界发育及其对巨型逆冲滑动行为的控制

• 批准号: 1559293
• 负责人: Nathan Bangs
• 金额: $ 52.81万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-07-01 至 2021-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1559293&HistoricalAwards=false
• 关键词: Collaborative; Research; Deep; imaging; south

As part of the "ring of fire," the western coast of South America is subject to frequent large earthquakes. This is because the oceanic plate is being thrust under (subducted) beneath the continent of South America. The high level of activity along the Chile margin makes it an excellent place to study how geologic structure can influence earthquake behavior, knowledge that can be transferred to other subduction zones around the world. The portion of the Chile margin that ruptured in 1960 seems to produce similar great earthquakes every 100 to 150 years whereas to the north the historical pattern is less regular, with several smaller earthquakes interspersed with occasional larger earthquakes. The goal of this project is to use seismic imaging tools available on the research vessel Langseth to look deep into this margin (up to ~15 km in depth) to characterize the physical properties of the boundary between the oceanic and continental plates that may control how it ruptures. The results will have broad societal impact by informing efforts to evaluate seismic hazards globally. This setting is a good analog to the Cascadia subduction zone off the westcoast of the US, and a better understanding of the Chilean megathrust should lead to more informed hazard forecasts and mitigation plans for Cascadia (and margins around the globe). The science team for the research cruise will include professors and students from the US and Chile (and possibly other countries) and provide hands-on training in seismic reflection data acquisition and processing. The research cruise will also be an opportunity to reach out both virtually (through student-led blogs) and in person (through ship tours in port) with school children and the general public. The south-central Chile subduction zone (34-47 degrees S) experienced the largest instrumentally-recorded earthquake (Mw 9.5) in 1960 and the sixth largest (Mw 8.8) in 2010 on an adjacent, overlapping segment to the north. The segment that ruptured during the 1960 event has a history of regular rupture of this entire 1000-km long segment, while the 500-km long segment that ruptured during the 2010 event usually ruptures in smaller (100 km) patches and at irregular intervals. Good slip models are available for both events as well as a model for interplate coupling leading up to the 2010 event. Because of the long earthquake history coupled with extensive modern constraints on interplate slip and interseismic coupling, this region is an excellent place to compare the along-strike differences in forearc geologic structure and determine their role in controlling these major along-strike differences in megathrust earthquake behavior. Several observations and hypotheses have been presented in recent years to explain the different slip behaviors observed in subduction zones globally. Foremost among these is the observation that the largest historic earthquakes (e.g. south-central Chile, Alaska, Sumatra and Cascadia) tend to be in thickly-sedimented subduction zones, possibly because a thick sediment cover leads to a smooth, homogeneous plate-boundary. This project will obtain seismic reflection data to image the detailed structure of the plate boundary at depth and determine how sediment on the incoming plate interacts with basement topography and whether sediment thickness controls the interaction between the upper and lower plates that leads to great earthquakes.

作为“火环”的一部分，南美洲西海岸经常发生大地震。 这是因为海洋板块被推入（俯冲）南美洲大陆下方。 智利边缘的高强度活动使其成为研究地质结构如何影响地震行为的绝佳场所，这些知识可以转移到世界其他俯冲带。 1960 年破裂的智利边缘部分似乎每 100 至 150 年就会产生类似的大地震，而在北部，历史模式不太规律，有几次较小的地震，偶尔也有较大的地震。该项目的目标是利用 Langseth 号研究船上提供的地震成像工具深入研究该边缘（深度可达约 15 公里），以表征海洋和大陆板块之间边界的物理特性，这些特性可能控制如何控制海洋板块和大陆板块之间的边界。它破裂了。研究结果将为全球地震灾害评估工作提供信息，从而产生广泛的社会影响。这种环境很好地模拟了美国西海岸附近的卡斯卡迪亚俯冲带，更好地了解智利的巨型逆冲断层应该可以为卡斯卡迪亚（以及全球边缘）提供更明智的灾害预测和缓解计划。 研究巡航的科学团队将包括来自美国和智利（可能还有其他国家）的教授和学生，并提供地震反射数据采集和处理方面的实践培训。这次研究巡游也将提供一个机会，通过虚拟方式（通过学生主导的博客）和面对面（通过港口的船舶游览）与学童和公众进行接触。 智利中南部俯冲带（南纬 34-47 度）在 1960 年经历了仪器记录的最大地震（兆瓦 9.5 级），并在 2010 年在北部相邻的重叠部分经历了第六次大地震（兆瓦 8.8 级）。 1960 年事件期间破裂的路段具有整个 1000 公里长的路段定期破裂的历史，而 2010 年事件期间破裂的 500 公里长的路段通常以较小的（100 公里）斑块和不规则的间隔破裂。 良好的滑移模型可用于这两项活动，以及 2010 年活动之前的板间耦合模型。 由于悠久的地震历史，加上现代对板间滑移和震间耦合的广泛限制，该地区是比较弧前地质结构沿走向差异并确定其在控制巨型逆冲地震中这些主要沿走向差异中的作用的绝佳场所行为。 近年来，人们提出了一些观察结果和假设来解释在全球俯冲带中观察到的不同滑移行为。其中最重要的是观察到历史上最大的地震（例如智利中南部、阿拉斯加、苏门答腊岛和卡斯卡迪亚）往往发生在沉积物厚的俯冲带，可能是因为厚的沉积物覆盖导致了光滑、均匀的板块边界。 该项目将获得地震反射数据，对板块边界的深度结构进行成像，并确定传入板块上的沉积物如何与基底地形相互作用，以及沉积物厚度是否控制了上下板块之间的相互作用，从而导致大地震。