A frequency-based parameter for rapid estimation of magnitude

This study introduce a new frequency parameter called sfcwt, which can be used to estimate earthquake magnitude on the basis of the first few seconds of P-waves, using the waveforms of earthquakes occurring in Japan. This new parameter is introduced using continuous wavelet transform as a tool for extracting the frequency contents carried by the first few seconds of P-wave. The empirical relationship between the logarithm of sfcwt within the initial 4 s of a waveformand magnitude was obtained. To evaluate the precision of sfcwt, we also calculated parameters smax p and sc. The average absolute values of observed and estimated magnitude differences (jMest Mobsj) were 0.43, 0.49, and 0.66 units of magnitude, as determined using smax p , sc, and sfcwt, respectively. For earthquakes with magnitudes greater than 6, these values were 0.34, 0.56, and 0.44 units of magnitude, as derived using smax p , sc, and sfcwt, respectively. The sfcwt parameter exhibited more precision in determining the magnitude of moderate- and small-scale earthquakes than did the sc-based approach. For a general range of magnitudes, however, the smax p -based method showed more acceptable precision than did the other two parameters.