Estimating seismic moment magnitude (Mw) of tremor bursts in northern Cascadia: Implications for the “seismic efficiency” of episodic tremor and slip

Authors

  • Honn Kao,

    1. Pacific Geoscience Centre, Geological Survey of Canada, Sidney, British Columbia, Canada
    2. School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada
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  • Kelin Wang,

    1. Pacific Geoscience Centre, Geological Survey of Canada, Sidney, British Columbia, Canada
    2. School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada
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  • Herb Dragert,

    1. Pacific Geoscience Centre, Geological Survey of Canada, Sidney, British Columbia, Canada
    2. School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada
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  • Jason Y. Kao,

    1. Division of Engineering Science, University of Toronto, Toronto, Ontario, Canada
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  • Garry Rogers

    1. Pacific Geoscience Centre, Geological Survey of Canada, Sidney, British Columbia, Canada
    2. School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada
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Abstract

[1] We develop a method to estimate the seismic moments of deep non-volcanic tremor bursts observed in northern Cascadia. For each tremor burst, the maximum amplitudes at individual stations within a time window ±5 s around the predicted arrivals of the S phase are measured and compared to the maximum S amplitudes measured from synthetic seismograms. The proposed method is thoroughly calibrated using 464 local earthquakes and the results show excellent consistency between the reported ML and the estimated Mw. We apply the method to northern Cascadia tremors and infer that most bursts have Mw∼1.0–1.7. The corresponding b value appears to be 1, consistent with that of ordinary earthquakes but over a narrower Mw range. Comparison of cumulative tremor Mw and the Mw estimated from the accompanying slow slip suggests that the “seismic efficiency” of the Episodic Tremor and Slip (ETS) is of the order of 0.1% or less.

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