An Open-Access, Controlled-Source Seismic Dataset Across the Cascadia Accretionary Wedge From Multi-Scale Regional OBS and Focused Large-N Nodal Arrays

大型逆冲地震和海啸等地质灾害发生在汇聚的边缘，在那里，构造力量将一个构造板块推拉到另一个板块之下。收敛边缘的一个例子是北美西部的卡斯卡迪亚俯冲区，在那里，胡安德富卡板块在加利福尼亚州、俄勒冈州、华盛顿州和不列颠哥伦比亚省北部沿海地区的缓慢持续下降，过去曾引发过大地震和相关的海啸。了解正在从胡安德富卡板块刮下并推送到北美板块上的沉积物的结构和物理性质是非常重要的，因为厚沉积物的存在增加了发生大地震的可能性。卡斯卡迪亚边缘的沉积物中含有大量的天然甲烷气体和其他流体。这些流体沿边缘的存在和变化对海床在地震期间的反应和震动有很大影响。该项目将沿着从海岸线附近延伸到俄勒冈州、华盛顿州和不列颠哥伦比亚省近海约100英里的一系列线路在海床上部署传感器(海底地震仪和节点)，以记录来自人造声脉冲以及自然发生的地震活动的信号。这些传感器记录的数据将使研究人员能够记录美国西海岸沉积物在地震中震动特性的变化。这些信息对于在未来大地震破裂的假设情景下预测美国西部的震动，以及评估地震造成的海啸和海底滑坡风险至关重要。该项目将与美国地质勘探局合作进行。该项目利用已经资助的卡斯卡迪亚边缘地震反射调查，通过收集一整套新的科学数据并扩大这些互补性开放获取数据集的潜在用户基础来增加科学回报。该项目的目标是获得一个涵盖整个卡斯卡迪亚边缘的开放获取的海洋广角地震反射/折射数据集。这项调查将包括部署和找回使用标准自由落体和声学释放技术的短周期多分量海底地震仪，以及部署和找回使用遥控运载工具从商业供应商处租用的大N个海底节点阵列。传感器将记录计划于2020年夏天在卡斯卡迪亚边缘附近进行的地震反射调查的受控源声波信号。收集的数据将是开放获取的，并将在获取后立即向社区发布，并进行质量控制检查。数据将被缩减为标准的数字格式，并以原始的连续数字时间序列的形式提供。地震仪和节点阵列将在不同的空间尺度上对地震波场进行采样，从而为获得卡斯卡迪亚吸积楔在三个互补尺度上的地震纵波和横波速度模型提供最佳的数据集：1.包含俯冲带全长的边缘尺度模型(约100公里横向分辨率)。2.从深海平原到大陆架的区域中分辨率断面(横向分辨率约10公里)。3.三条横断面的局部高分辨率模型(横向分辨率为数百米)，代表了明显的沉积楔形构造样式和已知的构造非均质性。该项目将提供急需的数据，以建立准确、多分辨率的卡斯卡迪亚吸积棱镜地下结构模型，填补改善卡斯卡迪亚地震和海啸危险评估的关键知识空白。这些数据将使研究人员能够利用各种最先进的方法在互补的空间尺度上开发模型，包括多参数二维弹性全波形反演，以解决多个高度重要的科学问题，例如：(A)记录沉积楔形场地响应的变化，这对于预测美国西部地震引发的震动和在未来大地震破裂的假设情景下评估海啸/山体滑坡危险至关重要，并测试拟议的古大地震与浊流分布之间的联系。(B)确定指示流体排出和/或滞留、排水网络及其与结构风格和海底流体海侵的关系的沉积属性(Vp、Vs、密度、孔隙度和流体孔压)。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。

Geologic hazards such as large megathrust earthquakes and tsunamis occur at convergent margins where tectonic forces push and drag one tectonic plate beneath another. One example of a convergent margin is the Cascadia Subduction Zone off western North America, where the slow ongoing descent of the Juan de Fuca plate beneath coastal northern California, Oregon, Washington and British Columbia has generated large earthquakes and associated tsunamis in the past. Knowledge of the structural and physical properties of the sediments that are being scraped off the Juan de Fuca plate and pushed onto the North American plate is of great importance because the presence of thick sediments increases the potential for great megathrust earthquakes. The scraped off sediments along the Cascadia margin contain significant amounts of naturally occurring methane gas and other fluids. The presence and variations of these fluids along the margin have a large impact on how the seabed responds and shakes during an earthquake. This project will deploy sensors (ocean bottom seismometers and nodes) on the seabed along a series of lines extending from near the coastline out to ~100 miles offshore Oregon, Washington and British Columbia to record signals from human-made acoustic pulses as well as from naturally occurring seismicity. The data recorded by these sensors will allow researchers to document variations in earthquake shaking properties of the sediments off the US west coast. Such information is critical for predicting shaking along the western US under hypothetical scenarios of future large earthquake rupture and assessing tsunami and submarine landslide hazards caused by earthquakes. This project will be conducted in partnership with the USGS. The project leverages an already funded seismic reflection survey of the Cascadia margin, increasing the scientific return by enabling a whole new suite of scientific data to be collected and broadening the base of potential users for these complementary open-access data sets.The goal of this project is to acquire an open-access, marine wide-angle seismic reflection/refraction dataset across the Cascadia accretionary wedge encompassing the full length of the margin. This survey will consist of the deployment and recovery of short-period multicomponent ocean bottom seismometers using standard free-fall and acoustic release techniques, and the deployment and recovery of large-N arrays of ocean bottom nodes leased from a commercial provider using a remotely operated vehicle. The sensors will record the controlled-source acoustic signals of a seismic reflection survey off the Cascadia margin planned for summer 2020. The data collected will be open-access and will be released to the community immediately after acquisition and checked for quality control. The data will be reduced to standard digital formats as well as provided as a raw continuous digital time series. The seismometer and nodal arrays will sample the seismic wavefields at different spatial scales, thus providing a data set that is optimal for obtaining seismic compressional- and shear-wave velocity models of the Cascadia accretionary wedge at three complementary scales: 1. A margin-scale model (~100-km lateral resolution) encompassing the full length of the subduction zone. 2. Regional, intermediate-resolution transects (~10-km lateral resolution) from the abyssal plain to the continental shelf. 3. Local, high-resolution models (hundreds-of-meters lateral resolution) across three transects representative of distinct accretionary wedge structural style and known structural heterogeneities. The project will provide much needed data to create accurate, multi-resolution models of the subsurface structure of the Cascadia accretionary prism, filling a critical knowledge gap for improving earthquake and tsunami hazard assessments for Cascadia. The data will enable researchers to develop models at complementary spatial scales using a variety of state-of-the-art methodologies, including multi-parameter 2-D elastic full waveform inversion, to address multiple scientific problems of high importance, such as: (a) Documenting variations in accretionary wedge site response, which is critical for predicting earthquake-triggered shaking along the western US and assessing tsunami/landslide hazards under hypothetical scenarios of future megathurst rupture, and to test proposed linkages between paleo great earthquakes and distribution of turbidites. (b) Determining accretionary sediment properties (Vp, Vs, density, porosity, and fluid pore pressure) indicative of fluid expulsion and/or retention, drainage networks, and their relation to structural style and seafloor fluid seepage.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.