Studies of Seismogenesis and Plate Boundary Structure on Canada's West Coast

加拿大西海岸地震成因和板块边界结构研究

• 批准号: RGPIN-2016-04239
• 负责人: Bostock, Michael
• 金额: $ 3.5万
• 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: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=614932
• 关键词: Studies; Seismogenesis; Plate; Boundary; Structure

Plate boundary faults endanger over 3 million people and societal infrastructure along Canada's west coast. The greatest seismic hazard arises from the Cascadia Subduction Megathrust that extends from northern California to northern Vancouver Island, approximately ~150 km west of the coastline. This plate boundary has experienced M=9+ earthquakes at intervals averaging ~550 years and is capable of generating tsunamis and ground shaking comparable to recent great earthquakes in Japan (2011) and Indonesia (2004). The second plate boundary of concern is the Queen Charlotte Fault that extends north of Vancouver Island along the coast of Haida Gwaii. In 1949 this fault generated Canada's largest historically recorded earthquake (M=8.1). On October 27 2012, a M=7.8 earthquake beneath Haida Gwaii spawned a small tsunami and highlighted the existence of an additional, major thrust fault dipping to the northeast beneath Moresby Island. The Cascadia Megathrust was once thought to be quiescent between major earthquakes. In 2001, Canadian scientists discovered a new form of deformation on deeper portions of this fault in the form of a quasi-periodic release of stress coined episodic tremor and slip (ETS). Every ~14 months the plate boundary between 25 and 40 km depth slips a few cm over a few days. This motion is equivalent to a "silent" M=6.5 earthquake but goes unnoticed by the general public as it fails to radiate significant seismic waves. It is accompanied, however, by a weak, quasi-harmonic tremor that has been shown to comprise a cascade of many repeating and interfering low frequency earthquakes (LFEs). The study of ETS and LFEs is important because they i) afford constraints on the area (and so ultimate magnitude) of megathrust rupture, ii) may act as triggering agents for megathrust rupture and, iii) provide insight into how plate boundaries operate at depth. This proposal seeks funding to investigate earthquake processes, and ETS in particular, with the ultimate objective of better informing earthquake hazard assessment on Canada's west coast. The research is divided into 5 objectives: a) employ scattered waves within tremor to image fine details of plate boundary faults and elucidate the physical conditions leading to ETS; b) perform tomography using LFEs, regular earthquakes and data from previous seismic experiments to image fluid generation, migration and consumption within the Cascadia subduction zone; c) undertake comparison studies of LFE/tremor scaling relations across multiple plate boundaries (Cascadia, Japan, San Andreas) to constrain underlying generative mechanisms; d) use repeating earthquakes on the Queen Charlotte fault as creep meters to constrain fault motions and stress regime over the past 20 years, in particular, before and after the October 2012 event; and e) develop new methods to analyze finite-dimensional characteristics of Cascadia earthquakes.

板界断层危害了300万人和加拿大西海岸的社会基础设施。最大的地震危险源于卡斯卡迪亚俯冲巨像，从北加州到北温哥华岛，在海岸线以西约150公里。该板边界以平均约550年的时间间隔经历了M = 9+地震，并且能够产生海啸和地面摇动，可与日本最近的大地震（2011）和印度尼西亚（2004年）相提并论。关注的第二个板块边界是夏洛特皇后的断层，该断层沿着海达·格瓦伊（Haida Gwaii）海岸延伸到温哥华岛以北。 1949年，这一故障产生了加拿大历史上最大的地震（M = 8.1）。 2012年10月27日，Haida Gwaii下方的A M = 7.8地震产生了一小块海啸，并强调了存在额外的大推力断层，浸入了莫尔斯比岛下方的东北部。 卡斯卡迪亚巨星曾经被认为是主要地震之间的静止。 2001年，加拿大科学家发现了一种新的形式的变形形式，以更深的部分的形式，其形式是应力造成的情节震颤和滑移（ETS）的准周期释放。每14个月，板块的深度在几天内就会在25至40公里的深度之间滑动几厘米。这种运动等同于“沉默” M = 6.5地震，但由于公众未能散发出明显的地震波，因此没有被公众注意到。但是，它伴随着弱的准谐波震颤，该震颤已被证明包括许多重复和干扰低频地震（LFES）的级联。对ETS和LFE的研究很重要，因为它们i）对大型破裂的区域（以及最终的幅度）构成限制，ii）可能是触发巨型破裂和iii的触发剂，并洞悉板边界如何在深度上运行。 该提案寻求资金来调查地震过程，尤其是ETS，其最终目标是更好地告知对加拿大西海岸的地震危险评估。该研究分为5个目标：a）在震颤中采用散射波，以图像板边界断层的细节并阐明导致ETS的物理条件； b）使用LFE，常规地震和来自以前的地震实验的数据进行层析成像，以图像Cascadia俯冲带内的流体产生，迁移和消耗； c）对多个板块边界（Cascadia，Japan，San Andreas）进行LFE/震颤缩放关系的比较研究来限制潜在的生成机制； d）使用夏洛特女王断层的重复地震作为蠕变仪，以限制过去20年中的断层动作和压力制度，特别是在2012年10月的活动之前和之后； E）开发新方法来分析卡斯卡迪亚地震的有限维度。