Magnitude estimation using the first three seconds P‐wave amplitude in earthquake early warning

[1] Pd is the peak amplitude of displacement in the first three seconds after the arrival of the P wave. We investigated the attenuation of Pd with the hypocentral distance R in southern California as a function of magnitude M, and obtained the following relationship: log (Pd )= � 3.463 + 0.729 � M � 1.374 � log (R) ± 0.305. Given an earthquake location determined by the P-wave arrival times at stations close to the epicenter, this relationship can be used to define a so-called ‘‘Pd magnitude’’ of earthquakes. Our result shows that for earthquakes in southern California the Pd magnitudes agree with the catalog magnitudes with a standard deviation of 0.18 for events less than magnitude 6.5. Therefore, Pd is a robust measurement for estimating the magnitudes of earthquakes and has practical application in earthquake early warning systems. Citation: Wu, Y.-M., and L. Zhao (2006), Magnitude estimation using the first three seconds P-wave amplitude in earthquake early warning, Geophys. Res. Lett., 33, L16312, doi:10.1029/2006GL026871.

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