A frequency-based parameter for rapid estimation of magnitude

Abstract

This study introduce a new frequency parameter called s fcwt , 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 s fcwt within the initial 4 s of a waveform and magnitude was obtained. To evaluate the precision of s fcwt , we also calculated parameters s max p and s c . The average absolute values of observed and estimated magnitude differences (jM est À M obs j) were 0.43, 0.49, and 0.66 units of magnitude, as determined using s max p , s c , and s fcwt , respectively. For earthquakes with magnitudes greater than 6, these values were 0.34, 0.56, and 0.44 units of magnitude, as derived using s max p , s c , and s fcwt , respectively. The s fcwt parameter exhibited more precision in determining the magnitude of moderate-and small-scale earthquakes than did the s c -based approach. For a general range of magnitudes, however, the s max p -based method showed more acceptable precision than did the other two parameters.