Shunroku Yamamoto
William L. Ellsworth
Shunta Noda
2016
<p><span>We propose a simple approach to measure earthquake magnitude </span><i>M</i><span> using the time difference (</span><i>T</i><sub><span>op</span></sub><span>) between the body‐wave onset and the arrival time of the peak high‐frequency amplitude in an accelerogram. Measured in this manner, we find that </span><i>M</i><sub><span>w</span></sub><span> is proportional to 2log</span><i>T</i><sub><span>op</span></sub><span> for earthquakes 5≤</span><i>M</i><sub><span>w</span></sub><span>≤7, which is the theoretical proportionality if </span><i>T</i><sub><span>op</span></sub><span> is proportional to source dimension and stress drop is scale invariant. Using high‐frequency (>2  Hz) data, the root mean square (rms) residual between </span><i>M</i><sub><span>w</span></sub><span> and </span><i>M</i><sub><span><i>T</i><span>op</span></span></sub><span>(</span><i>M</i><span> estimated from </span><i>T</i><sub><span>op</span></sub><span>) is approximately 0.5 magnitude units. The rms residuals of the high‐frequency data in passbands between 2 and 16 Hz are uniformly smaller than those obtained from the lower‐frequency data. </span><i>T</i><span>op</span><span> depends weakly on epicentral distance, and this dependence can be ignored for distances <200  km. Retrospective application of this algorithm to the 2011 Tohoku earthquake produces a final magnitude estimate of </span><i>M</i><span> 9.0 at 120 s after the origin time. We conclude that </span><i>T</i><sub><span>op</span></sub><span> of high‐frequency (>2  Hz) accelerograms has value in the context of earthquake early warning for extremely large events.</span></p>
application/pdf
10.1785/0120150108
en
Seismological Society of America
Rapid estimation of earthquake magnitude from the arrival time of the peak high‐frequency amplitude
article