A frequency-based parameter for rapid estimation of magnitude

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