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，南美西海岸经常发生大地震。 这是因为海洋板正被推向南美洲大陆的（俯冲）下方。 沿智利边缘的高水平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各地的其他俯冲区。 1960年破裂的智利边缘的一部分似乎每100至150年就会产生类似的大地震，而在北部，历史模式不那么规律，几个较小的地震偶尔会偶尔发生较大的地震。该项目的目的是使用Langseth研究船上可用的地震成像工具深入研究该边缘（深度〜15公里），以表征海洋和大陆板之间边界的物理特性，以控制其破裂方式。通过告知全球地震危害的努力，结果将产生广泛的社会影响。这种环境与美国西岸的卡斯卡迪亚俯冲区相似，对智利巨型巨星的更好理解应导致更明智的危害预测和缓解卡斯卡迪亚的缓解计划（以及全球范围内的利润率）。 研究巡游的科学团队将包括来自美国和智利（可能还有其他国家 /地区）的教授和学生，并在地震反射数据获取和处理方面提供动手培训。研究巡游还将是一个实际上（通过学生主导的博客）和与学童和公众的人（通过港口的船舶之旅）联系的机会。 1960年，中南部智利俯冲带（34-47度）在1960年经历了最大的乐器录制地震（MW 9.5），2010年在北部的一个重叠段上是2010年的第六大地震（MW 8.8）。在1960年事件中破裂的部分具有整个1000公里长的段的常规破裂病史，而在2010年事件中破裂的500公里长的段通常在较小（100 km）的斑块和不规则的间隔中破裂。 良好的滑道模型都适用于事件，也可以使用导致2010年事件的车型耦合模型。 由于地震历史悠久，再加上对板间滑动和跨层耦合的广泛现代限制，该区域是比较前臂地质结构中沿袭的绝佳场所，并确定它们在控制这些主要的巨型震颤地震行为方面的作用。 近年来，已经提出了几种观察结果和假设，以解释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，最大的历史地震（例如中南部智利，阿拉斯加，苏门答腊和卡斯卡迪亚）往往是在厚实的俯冲带中，可能是因为厚实的沉积物覆盖层导致光滑的，均匀的均匀板块构成式板块。 该项目将获得地震反射数据，以对深度处的板界边界的详细结构进行成像，并确定输入板上的沉积物如何与地下室地形相互作用，以及沉积物厚度是否控制上层和下部板之间的相互作用，从而导致大地震。