Collaborative Research: Illuminating the Cascadia plate boundary zone and accretionary wedge with a regional-scale ultra-long offset multi-channel seismic study

合作研究：通过区域尺度超长偏移多道地震研究阐明卡斯卡迪亚板块边界带和增生楔

• 批准号: 1827363
• 负责人: Shuoshuo Han
• 金额: $ 9万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-11-01 至 2022-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1827363&HistoricalAwards=false
• 关键词: Collaborative; Research; Illuminating; Cascadia; plate

At the Cascadia Subduction Zone, the slow ongoing descent of the Juan de Fuca plate beneath the northwestern coast of North America has generated large earthquakes and associated tsunami in the past. Geologic records suggest that some sections of the subduction zone fault or "megathrust", which extends ~35-90 miles seaward from the coasts of northern California all the way to southern British Columbia, slipped less than other sections during the last large earthquake (1700 AD), and that in some prior EQ only parts of the subduction zone ruptured. Whether these along-margin variations may persist in future EQ has important implications for quantifying earthquake and tsunami hazards within the heavily populated Pacific Northwest margin. Geologic structure such as seamounts and other topographic features in the descending Juan de Fuca plate, the structure and properties of the thick folded and faulted package of sediments that forms above the subduction zone fault, or the properties of megathrust fault rocks, could contribute to these along-margin variations. However the current observations are limited and allow for a wide range of possible future earthquake scenarios. Modern marine seismic reflection imaging techniques provide the best tools available for illuminating a subduction zone to the depths of the earthquake source region and below. The overall goal of this project is to acquire a regional grid of modern marine seismic reflection data spanning the entire Cascadia Subduction zone to image how the geologic structure and properties of this subduction zone vary both along and across the margin. This project will serve the national interest in that the acquired data will form a foundational dataset for future initiatives focused on hazard assessment in the U.S. Pacific Northwest, including for an earthquake early warning network and deep drilling to sample the fault zone rocks, and it will promote the advancement of science by providing a new regional framework relevant for the wide range of multi-disciplinary onshore and offshore studies conducted in this region over the past several decades.Specifically, this study will use ultra-long-offset multi-channel seismic (MCS) data to characterize subducting plate and accretionary wedge structure, and properties of the megathrust, to address the following specific questions: 1. Are there any systematics in the structure and properties of the incoming Juan de Fuca plate, the megathrust zone, and accretionary wedge associated with inferred paleo-rupture segmentation? 2. Are there down-dip variations in megathrust geometry and reflectivity indicative of transitions in fault properties, and what are the properties of the potentially tsunamigenic shallow portion of the megathrust? Long 15-km-offset MCS data will be acquired along twenty 2-D profiles at 50-100 km spacing oriented perpendicular to the margin and located to provide coverage in areas inferred to be paleo-rupture patches and their boundary zones. The survey will also include one continuous strike line along the continental shelf centered roughly over gravity-inferred fore-arc basins to investigate possible segmentation near the down-dip limit of the seismogenic zone. The margin normal lines will extend approximately 50 km seaward of the deformation front to image the region of subduction bend faulting in the incoming oceanic plate, and landward of the deformation front to as close to the shoreline as can be safely maneuvered. The acquired data will be designed to characterize 1) the deformation and topography of the incoming plate, 2) the depth, topography and reflectivity of the megathrust, 3) sediment properties and amount of sediment subduction, 4) the structure and evolution of the accretionary wedge, including geometry and reflectivity of fault networks, and how these properties vary along strike, spanning the full length of the margin and down dip across what may be the full width of the seismogenic zone at Cascadia. The data will be processed to pre-stack depth migration using state-of-the art seismic processing techniques and will be made openly available to the community, providing a high-quality data set illuminating the regional subsurface architecture all along the Cascadia Subduction Zone.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

在卡斯卡迪亚俯冲带，胡安德富卡板块在北美西北海岸下方缓慢持续下降，过去曾引发过大地震和相关海啸。地质记录表明，俯冲带断层或“巨型逆冲断层”的某些部分从加利福尼亚州北部海岸向海延伸约 35-90 英里，一直延伸到不列颠哥伦比亚省南部，在上次大地震（1700 年）期间，其滑动量比其他部分要少。 AD），并且在一些先前的 EQ 中，只有部分俯冲带破裂。这些边缘变化是否会在未来的EQ中持续存在，对于量化人口稠密的太平洋西北边缘内的地震和海啸灾害具有重要意义。地质结构，例如胡安德富卡下降板块中的海山和其他地形特征，俯冲带断层上方形成的厚厚的褶皱和断层沉积物的结构和性质，或巨型逆冲断层岩的性质，可能有助于这些沿边际变化。然而，目前的观测结果是有限的，并且考虑到了未来可能出现的各种地震情景。现代海洋地震反射成像技术提供了最好的工具，可用于照亮俯冲带至震源区及以下的深度。该项目的总体目标是获取跨越整个卡斯卡迪亚俯冲带的现代海洋地震反射数据的区域网格，以了解该俯冲带的地质结构和特性如何沿边缘和跨边缘变化。该项目将服务于国家利益，因为所获取的数据将为未来专注于美国太平洋西北地区灾害评估的举措形成基础数据集，包括地震早期预警网络和对断层带岩石取样的深钻探，并且它将通过提供一个新的区域框架来促进科学的进步，该框架与过去几十年来在该地区进行的广泛的多学科陆上和海上研究相关。具体来说，这项研究将使用超长偏移距多道地震（ MCS）数据表征俯冲板块和增生楔结构以及巨型逆冲断层的性质，以解决以下具体问题： 1. 传入的胡安·德富卡板块、巨型逆冲断层带和增生楔的结构和性质是否存在与推断古地层相关的系统学-断裂分割？ 2. 巨型逆冲断层的几何形状和反射率是否存在指示断层性质转变的下倾变化，以及巨型逆冲断层的潜在海啸浅部的特性是什么？长 15 公里偏移的 MCS 数据将沿着 20 个 2-D 剖面以 50-100 km 的间距采集，垂直于边缘定向，并定位以提供推断为古断裂斑块及其边界区域的覆盖范围。该调查还将包括沿着大陆架的一条连续走向线，大致集中在重力推断的弧前盆地上方，以调查地震发生带下倾极限附近可能的分割。边缘法线将向变形前缘向海延伸约 50 公里，以对进入的海洋板块中的俯冲弯曲断层区域进行成像，并向变形前缘向陆地延伸至可安全操纵的尽可能接近海岸线的位置。 所获取的数据将用于表征 1) 传入板块的变形和地形，2) 巨型逆冲断层的深度、地形和反射率，3) 沉积物性质和沉积物俯冲量，4) 增生的结构和演化楔形，包括断层网络的几何形状和反射率，以及这些特性如何沿走向变化，跨越整个边缘长度和下倾，跨越可能是卡斯卡迪亚地震发生带的整个宽度。这些数据将使用最先进的地震处理技术进行叠前深度偏移处理，并将向社区公开提供，提供高质量的数据集，阐明卡斯卡迪亚俯冲带沿线的区域地下结构。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。