Rapid Estimation of Earthquake Magnitude from the Arrival Time of the Peak High-Frequency Amplitude

摘要

We propose a simple approach to measure earthquake magnitude M using the time difference (T-op) 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 M-w is proportional to 2 log T-op for earthquakes 5 <= M-w <= 7, which is the theoretical proportionality if T-op is proportional to source dimension and stress drop is scale invariant. Using high-frequency (>2 Hz) data, the root mean square (rms) residual between M-w and M-Top (M estimated from T-op) 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. T-op 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 M 9.0 at 120 s after the origin time. We conclude that T-op of high-frequency (>2 Hz) accelerograms has value in the context of earthquake early warning for extremely large events.