Complex Structure in the Nootka Fault Zone Revealed by Double-Difference Tomography and a New Earthquake Catalog
Complex Structure in the Nootka Fault Zone Revealed by Double-Difference Tomography and a New Earthquake Catalog
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DOI：
10.1029/2021gc010205
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发表时间：
2022-02-01
影响因子：
3.5
通讯作者：
Roecker, Steven W.
中科院分区：
文献类型：
--
作者：
Merrill, Reid J.;Bostock, Michael G.;Roecker, Steven W.
我们对不列颠哥伦比亚省西南部2000年至2020年间记录的地震波波形采用了一种自动地震检测算法，与现有加拿大地质调查局目录中的21,538个地震事件相比，我们定位了32,121个至少具有三个配对P波和s波到达时间的地震事件。该增强目录用于温哥华岛的双差地震断层成像，特别关注Nootka断裂带（NFZ）。NFZ是Juan de Fuca板块和Explorer板块在分布的左侧走滑断裂带中的转换边界。层析成像结果表明，NFZ内存在双地震带，与俯冲带中常见的Vp/Vs结构平行。具体来说，高Vp/Vs的倾斜层是由降低Vp/Vs的材料支撑的。3 Mw bbbb60事件及其余震揭示了构造的复杂性。Vp/Vs结构进一步表明探险者板块逆冲下海洋岩石圈延伸至布鲁克斯半岛下方20 km深度。我们的研究结果支持了这样的假设，即NFZ代表了一个结构独立的海洋岩石圈，它表现出(a)比通常描述的更北的轨迹，(b)与胡安·德·富卡或探险家板块相比，板块曲率增加。
We employ an automatic earthquake detection algorithm to seismic waveforms recorded between the years 2000 and 2020 in southwest British Columbia. 32,121 events which possess at least three paired P- and S-wave arrival times are located, compared to 21,538 seismic events in the existing Geologic Survey of Canada catalog. This augmented catalog is employed for double-difference seismic tomography across Vancouver Island, with particular focus on the Nootka Fault zone (NFZ). The NFZ is a transform boundary that separates the Juan de Fuca and Explorer plates in a zone of distributed left-lateral strike-slip faulting. Tomographic results indicate that a double seismic zone exists within the NFZ that parallels Vp/Vs structure typically observed in subduction zones. Specifically, a dipping high Vp/Vs layer is underlain by reduced Vp/Vs material. Structural complexities are revealed by three Mw > 6 events and their aftershocks. The 2004 Mw 6.3 and 2011 Mw 6.4 events are interpreted to reside southeast of the NFZ within the Juan de Fuca plate at depths as shallow as 20 km, and the 2014 Mw 6.6 event is interpreted to reside within oceanic lithosphere of the NFZ at depths >35 km. Vp/Vs structure further indicates that underthrust oceanic lithosphere of the Explorer plate extends to 20 km depth beneath Brooks Peninsula. Our results support the hypothesis that the NFZ represents a structurally independent slice of oceanic lithosphere that exhibits (a) a more northerly trajectory than typically depicted, and (b) increased plate curvature when compared to either the Juan de Fuca or Explorer plates.