Magnitudes and moment-duration scaling of low-frequency earthquakes beneath southern Vancouver Island
Magnitudes and moment-duration scaling of low-frequency earthquakes beneath southern Vancouver Island
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DOI：
10.1002/2015jb012195
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发表时间：
2015-09-01
影响因子：
3.9
通讯作者：
Rubin, A. M.
中科院分区：
文献类型：
--
作者：
Bostock, M. G.;Thomas, A. M.;Rubin, A. M.
我们使用 130 个代表温哥华岛南部板块边界上的震源的低频地震 (LFE) 模板来检查 LFE 震级。每个模板由数百到数千个单独的 LFE 组装而成，代表 2003 年至 2013 年间主要阵发性震颤和滑动 (ETS) 事件的超过 269,000 次独立检测。在许多台站，近震中距离处的直接 P 波和 S 波的模板位移波形非常简单，接近均匀介质中点位错源预期的零相位、单脉冲。模板匹配过滤检测的高时空精度有利于各个 LFE 检测和波形分析的精确对准。在对一维几何扩散、衰减、自由表面放大和辐射方向图进行校正后，我们求解了一个大型稀疏线性系统，用于与单个 ETS 模板相对应的所有检测的 3D 路径校正和 LFE 幅度。震级的时空分布表明，当潮汐敏感性较低时，总力矩释放的一半通常发生在 ETS 事件期间 LFE 活动的前 12-24 小时内。其余部分会在几天内爆发式释放，特别是在空间广泛的快速震颤反转（RTR）期间，潮汐敏感性很高。 RTR 的特点是大幅度的 LFE，并且在 ETS 过渡区的上倾部分表达最为强烈，而在下倾水平则组织较少。 LFE 幅度-频率关系可以通过幂律比指数分布更好地描述，尽管它们表现出非常高的 b 值，接近 5。我们通过使用限制幅度范围（M-W）的检测生成模板来检查 LFE 矩-持续时间缩放。
We employ 130 low-frequency earthquake (LFE) templates representing tremor sources on the plate boundary below southern Vancouver Island to examine LFE magnitudes. Each template is assembled from hundreds to thousands of individual LFEs, representing over 269,000 independent detections from major episodic-tremor-and-slip (ETS) events between 2003 and 2013. Template displacement waveforms for direct P and S waves at near epicentral distances are remarkably simple at many stations, approaching the zero-phase, single pulse expected for a point dislocation source in a homogeneous medium. High spatiotemporal precision of template match-filtered detections facilitates precise alignment of individual LFE detections and analysis of waveforms. Upon correction for 1-D geometrical spreading, attenuation, free surface magnification and radiation pattern, we solve a large, sparse linear system for 3-D path corrections and LFE magnitudes for all detections corresponding to a single-ETS template. The spatiotemporal distribution of magnitudes indicates that typically half the total moment release occurs within the first 12-24h of LFE activity during an ETS episode when tidal sensitivity is low. The remainder is released in bursts over several days, particularly as spatially extensive rapid tremor reversals (RTRs), during which tidal sensitivity is high. RTRs are characterized by large-magnitude LFEs and are most strongly expressed in the updip portions of the ETS transition zone and less organized at downdip levels. LFE magnitude-frequency relations are better described by power law than exponential distributions although they exhibit very high b values approximate to 5. We examine LFE moment-duration scaling by generating templates using detections for limiting magnitude ranges (M-W