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沿着近300万人和社会基础设施。它们包括温哥华岛和海达岛近海的“巨型逆冲断层”板块边界，以及北美和胡安德富卡板块内更靠近人口中心（如温哥华和维多利亚）的规模较小但危险的结构。建议的研究计划提高了我们对这些结构的理解（以及我们减轻其相关危害的能力）通过A）将最先进的自动地震检测算法应用于公众可访问的地震波形档案，B）同时恢复地球的速度结构和精确的地震重新定位，以及C）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算法的自动化和应用。初步分析表明，大约3倍，目前存在于加拿大地质调查目录中的地震可以检测到使用非特定的自动检测算法，和10倍，目前编目的地震可以确定的因素时，模板匹配算法，搜索波形类似于已知的事件，随后采用。这些算法提供精确的到达时间，振幅和波形的极性，将用于两个后续阶段的分析。首先，高精度的相对到达时间允许详细的地下地质及其与孕震结构的关系，使用双差层析成像的分辨率，使洞察动力学过程负责在不同的构造环境中的地震。其次，我们小组利用小地震的波形振幅和极性进行矩张量反演的最新进展。地震矩张量是断层几何形状和滑动的点源表示。给定区域的多个独立矩张量的可用性使得能够计算区域应力场，从而进行地震危险性评估。由于小地震占压倒性优势的目录，我们的方法将允许详细分析的细尺度，时空变化的应力制度的特点广泛的构造环境，在西部不列颠哥伦比亚省。特别是，由不同的HQP进行的有针对性的区域研究将调查温哥华岛和海达岛近海的板块边界、温哥华岛的地壳断层、努特卡断层带、夏洛特女王三重接合区和海岸剪切带。该计划的结果将在以下方面产生重大影响：a）地震危险性评估，B）导致地震发生的物理过程的理解，以及c）岩石圈结构和演化的描述，沿着加拿大西海岸。