Collaborative Research: Relationship between plate boundary obliquity, strain accommodation, and fault zone geometry at oceanic-continental transforms: The Queen Charlotte Fault

合作研究：洋-陆转换时板块边界倾斜度、应变调节和断层带几何形状之间的关系：夏洛特皇后断层

• 批准号: 2128783
• 负责人: Emily Roland
• 金额: $ 39.76万
• 依托单位: Western Washington University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-03-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2128783&HistoricalAwards=false
• 关键词: Collaborative; Research; Relationship; between; plate

Often called the "San Andreas of the North", the Queen Charlotte fault (QCF) system is a strike-slip plate boundary that separates the Pacific and North American tectonic plates offshore western Canada and Southeast Alaska. The QCF is arguably the most active fault of its type in the world: the entire ~900 km offshore length has ruptured in seven M7 earthquakes during the last century and it sustains the highest known deformation rates (50 mm/yr). The fault system represents the largest seismic hazard to southeastern Alaska and Canada outside of Cascadia, and caused Canada?s largest recorded earthquake (M8.1) in 1949. Despite rapid response efforts following M7 earthquakes in 2012 and 2013, first-order questions regarding how the fault system deforms and the processes controlling fault failure during earthquakes remain unanswered due to the lack of modern geophysical imaging. This experiment will be the first comprehensive attempt to characterize this plate boundary at depth on a regional scale. Using seismic energy from marine acoustic and earthquake sources, the project will measure the depth and extent of seismicity, image the fault zone at depth, and determine velocity and thermal structure across the fault. All these data will lead to an improved understanding of this, and other major strike-slip fault systems, for better hazard assessment and earthquake forecasting. The science team is a collaborative, international group of US and Canadian researchers, led by three early-career women. Outreach to local communities will be conducted through a residency at the Sitka Science Center in Alaska and lectures at local high schools and community centers. Compared to convergent continental-oceanic plate boundaries, the time-space evolution of continental-oceanic transform margins is understudied, despite their important role in the planet?s plate tectonic system. Continental-oceanic transform faults are potentially one of the most favorable tectonic settings for subduction initiation due to the juxtaposition of lithospheres of contrasting density and thermal structure -- small degrees of convergence can lead to failure. The QCF system provides an ideal location to investigate how a continental-oceanic transform fault responds to systematically increasing degrees of convergence at the lithospheric scale. The study area includes two potential fault segment boundaries that mark abrupt changes in transpressive deformation mechanisms as suggested by changes in seafloor morphology and shallow seismic reflection structure: strain partitioning and underthrusting in the south transition to highly localized strike-slip deformation in the north. Lack of information on microseismic depths and locations, the deformation history and geometries of faults at depth, and lithospheric velocity structure leave multiple fundamental questions unanswered: Why has the QCF formed where it is, and what is its deformation history? What is the history of PAC underthrusting along the margin and the fate of underthrust material north of the area of maximum convergence? What are the primary physical conditions controlling seismogenesis along oceanic-continental transforms? How are strike-slip and compressive strain accommodated and partitioned over geologic and seismogenic timescales? Using a combined active- and passive-source marine seismic imaging strategy, this research will characterize crustal and uppermost mantle velocity structure, fault zone architecture and rheology, and seismicity. Data will be acquired using long-offset 2D seismic reflection and wide-angle reflection-refraction capabilities of the R/V Marcus G. Langseth and a combined US-Canadian broadband ocean bottom seismometer array of 64 instruments deployed for ~1 year.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.

夏洛特皇后断层 (QCF) 系统通常被称为“北方的圣安德烈亚斯”，是一个走滑板块边界，将加拿大西部和阿拉斯加东南部近海的太平洋和北美构造板块分开。 QCF 可以说是世界上同类断层中最活跃的断层：整个约 900 公里的离岸长度在上个世纪的七次 M7 地震中破裂，并且维持着已知的最高变形率（50 毫米/年）。该断层系统是阿拉斯加东南部和加拿大卡斯卡迪亚以外最大的地震危害，并在 1949 年引发了加拿大有记录的最大地震 (M8.1)。尽管在 2012 年和 2013 年发生 M7 地震后迅速做出了反应，但关于由于缺乏现代地球物理成像，断层系统如何变形以及地震期间控制断层破坏的过程仍然没有答案。该实验将是在区域尺度上深度表征该板块边界的首次综合尝试。该项目将利用海洋声波和地震源的地震能量来测量地震活动的深度和范围，对深度断层带进行成像，并确定断层上的速度和热结构。所有这些数据将有助于加深对这一断层系统以及其他主要走滑断层系统的了解，以便更好地进行灾害评估和地震预报。该科学团队是一个由美国和加拿大研究人员组成的国际协作小组，由三名早期职业女性领导。将通过在阿拉斯加锡特卡科学中心的驻场实习以及在当地高中和社区中心的讲座来向当地社区进行推广。与会聚的大陆-海洋板块边界相比，大陆-海洋转换边缘的时空演化尚未得到充分研究，尽管它们在地球板块构造系统中发挥着重要作用。由于密度和热结构不同的岩石圈并置，大陆-海洋转换断层可能是俯冲起始最有利的构造环境之一——小程度的收敛可能导致失败。 QCF 系统提供了一个理想的位置来研究大陆-海洋转换断层如何响应岩石圈尺度上系统性增加的收敛程度。研究区包括两个潜在的断层段边界，这些断层边界标志着海底形态和浅层地震反射结构的变化所表明的压变形机制的突然变化：南部的应变分割和逆冲向北部的高度局部化的走滑变形过渡。由于缺乏微震深度和位置、深部断层变形历史和几何形状以及岩石圈速度结构等方面的信息，导致多个基本问题没有得到解答：为什么 QCF 会在其所在位置形成，其变形历史是什么？ PAC 沿边缘逆冲的历史以及最大汇聚区域以北逆冲物质的命运是什么？控制洋-陆转换地震发生的主要物理条件是什么？ 如何在地质和地震时间尺度上调节和划分走滑应变和压缩应变？这项研究将采用主动和被动源海洋地震成像相结合的策略，描述地壳和上地幔的速度结构、断层带结构和流变性以及地震活动性。将使用 R/V Marcus G. Langseth 的长偏移距 2D 地震反射和广角反射折射功能以及部署约 1 年的由 64 台仪器组成的美国-加拿大宽带海底地震仪组合阵列来采集数据。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。