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

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 M-L and the estimated M-w. We apply the method to northern Cascadia tremors and infer that most bursts have M-w similar to 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. Citation: Kao, H., K. Wang, H. Dragert, J. Y. Kao, and G. Rogers (2010), Estimating seismic moment magnitude (Mw) of tremor bursts in northern Cascadia: Implications for the seismic efficiency of episodic tremor and slip, Geophys. Res. Lett., 37, L19306, doi: 10.1029/2010GL044927.