期刊
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
卷 120, 期 9, 页码 6329-6350出版社
AMER GEOPHYSICAL UNION
DOI: 10.1002/2015JB012195
关键词
low-frequency earthquakes; moment magnitude; moment-duration scaling; slow earthquakes; subduction zone
资金
- NSERC [RGPIN 138004]
- NSF EAR-PF [1249775]
- NSF [EAR 1344948]
- Directorate For Geosciences
- Division Of Earth Sciences [1344948] Funding Source: National Science Foundation
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<1.5, M(W)2.0). LFE duration displays a weaker dependence upon moment than expected for self-similarity, suggesting that LFE asperities are limited in fault dimension and that moment variation is dominated by slip. This behavior implies that LFEs exhibit a scaling distinct from both large-scale slow earthquakes and regular seismicity.
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