Seismotectonics of Canada's West Coast

加拿大西海岸的地震构造

• 批准号: RGPIN-2021-03039
• 负责人: Bostock, Michael
• 金额: $ 2.62万
• 依托单位: University of British Columbia
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=742343
• 关键词: Seismotectonics; Canada; West; Coast

Seismically active faults associated with plate tectonic processes endanger almost 3M people and societal infrastructure along Canada's west coast. They include "megathrust" plate boundaries offshore Vancouver Island and Haida Gwaii as well as smaller scale but comparably hazardous structures within the North American and Juan de Fuca plates in closer proximity to population centers like Vancouver and Victoria. The proposed research program improves our understanding of these structures (and so our ability to mitigate their associated hazards) through A) application of state-of-the-art automatic earthquake detection algorithms to publicly accessible seismic waveform archives, B) simultaneous recovery of Earth's velocity structure and precise earthquake relocation, and C) automation and application of a novel algorithm that we recently developed for quantifying fault parameters and the stress regime of small earthquakes. Preliminary analyses demonstrate that approximately 3 times as many earthquakes as currently exist in the Geological Survey of Canada catalogue can be detected using non-specific automatic detection algorithms, and that a factor of 10 times as many earthquakes as currently catalogued can be identified when template matching algorithms that search for waveforms similar to known events are subsequently employed. These algorithms supply accurate arrival-times, amplitudes and polarities of waveforms that will be used in two subsequent stages of analysis. First, high-precision relative arrival-times permit the resolution of detailed subsurface geology and its relation to seismogenic structures using double-difference tomography, enabling insights into dynamic processes responsible for earthquakes in different tectonic environments. Second, recent advances in moment tensor inversion by our group harness waveform amplitudes and polarities of small earthquakes. An earthquake moment tensor is a point-source representation of fault geometry and slip. The availability of multiple independent moment tensors for a given area enables calculation of the regional stress field and therefore seismic risk assessment. Since small earthquakes overwhelmingly dominate catalogues, our approach will allow detailed analysis of fine-scale, spatio-temporal variations in the stress regime characterizing the wide range of tectonic environments represented in western British Columbia. In particular, regionally targeted studies undertaken by diverse HQP will investigate the plate boundaries offshore Vancouver Isand and Haida Gwaii, crustal faults on Vancouver Island, the Nootka Fault Zone, the Queen Charlotte triple junction region, and the Coast Shear zone. Results from this program will lead to significant impacts in  a) assessment of seismic hazard, b) understanding of the physical processes leading to seismogenesis, and c) description of lithospheric structures and evolution, along Canada's west coast.

与板块构造过程相关的地震活动断层危及加拿大西海岸近 300 万人和社会基础设施，其中包括温哥华岛和海达瓜伊近海的“巨型逆冲断层”板块边界，以及北美和胡安德富卡境内规模较小但相对危险的结构。拟议的研究计划通过 A）最先进的应用提高了我们对这些结构的了解（以及减轻其相关危害的能力）。自动地震检测算法可公开访问的地震波形档案，B）同时恢复地球速度结构和精确的地震重定位，以及C）自动化和应用我们最近开发的用于量化断层参数和小地震应力状态的新颖算法。初步分析表明，使用非特定自动检测算法可以检测到加拿大地质调查局目录中现有地震数量的大约 3 倍，并且可以识别出当前目录中地震数量的 10 倍当随后采用搜索与已知事件相似的波形的模板匹配算法时，这些算法提供将在两个后续分析阶段中使用的准确的到达时间、幅度和极性。使用双差层析成像技术解析详细的地下地质及其与发震结构的关系，从而能够深入了解不同构造环境中地震的动态过程。其次，我们小组利用波形进行矩张量反演的最新进展。小地震的振幅和极性。地震矩张量是断层几何和滑移的点源表示，给定区域有多个独立的矩张量，可以计算区域应力场，从而进行小地震风险评估。压倒性地主导目录，我们的方法将允许对描述不列颠哥伦比亚省西部广泛的构造环境的应力状态的精细尺度、时空变化进行详细分析，特别是由不同的 HQP 进行的区域有针对性的研究。调查温哥华岛和海达瓜伊近海的板块边界、温哥华岛的地壳断层、努特卡断层带、夏洛特皇后三重交界区和海岸剪切带。该计划的结果将对 a) 地震评估产生重大影响。灾害，b) 了解导致地震发生的物理过程，以及 c) 描述加拿大西海岸的岩石圈结构和演化。