Seismotectonics of Canada's West Coast

与板块构造过程相关的地震活跃断层危及加拿大西海岸近300万人和社会基础设施。它们包括温哥华岛和海达瓜伊附近的“巨型逆冲”板块边界，以及北美板块和胡安·德·富卡板块内规模较小但相对危险的结构，这些板块更靠近温哥华和维多利亚等人口中心。拟议的研究计划通过A)应用最先进的自动地震检测算法来公开访问地震波形档案，B)同步恢复地球的速度结构和精确的地震定位，提高了我们对这些结构的理解（从而提高了我们减轻其相关危害的能力）。C)自动化和应用我们最近开发的一种新算法，用于量化断层参数和小地震的应力状态。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目前存在的大约3倍的地震，并且当随后使用模板匹配算法搜索与已知事件相似的波形时，可以识别出目前目录中地震数量的10倍。这些算法提供了精确的到达时间、振幅和波形的极性，这些波形将在随后的两个分析阶段使用。首先，高精度的相对到达时间允许使用双差层析成像技术来解析详细的地下地质及其与发震构造的关系，从而能够深入了解不同构造环境中导致地震的动态过程。第二，本小组利用小地震波形振幅和极性反演矩张量的最新进展。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可以计算区域应力场，从而进行地震风险评估。由于小地震在地震目录中占绝大多数，我们的方法将允许详细分析英属哥伦比亚西部大范围构造环境特征的应力状态的精细尺度、时空变化。特别是，由不同HQP进行的区域针对性研究将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、努特卡断裂带、夏洛特女王三重接合区和海岸剪切带。该项目的研究结果将对以下方面产生重大影响：1)地震危险性评估；2)了解导致地震发生的物理过程；3)描述加拿大西海岸岩石圈结构和演化。

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.