Abstract
In this study, we measure the seismic radiation energy, E(subscript s), and seismic moment, M(subscript o), of twenty-two larger-sized after shocks with 5.1≤M(subscript L)≤6.5 of the 1999 M(subscript s) 7.6 Chi-Chi, Tai wan, earth quake from high-quality digital strong-motion data recorded at stations with epicentral distances of less than 50 km through a method pro posed by Andrews (1986). We also eliminate the effects on the measures of E(subscript s) and M(subscript o) due to site amplification and finite frequency band width limitation. Comparison of the values of M(subscript o) obtained in this study and those listed in the Harvard CMT catalogue shows that Andrews' method to mea sure M(subscript o) from lo cal seismograms is acceptable. The measured values are E(subscript s)=2.0×10^18-8.9×10^21 g cm^2 sec^(-2) and M(subscript o)=1.3×10^23-1.4×10^26 g cm sec^(-2) cm^(-1), which give the scaled energy to be E(subscript s)/M(subscript o)=7.4×10^(-6)-2.6×10^(-4). The scaled energies of the 22 events are de pendent upon earth quake magnitude, M(subscript s), when both E(subscript s) and M(subscript o) are evaluated from lo cal seismograms; yet, in de pendent of M(subscript s) when M(subscript o) is estimated from teleseismic data. Scaled energy slightly depends on the depth, h (in km), through the following form: E(subscript s)/M(subscript o)=1.92×10^(-5)e(superscript 0.09h). In addition, the corner frequency, f(subscript c), is also measured. Its value ranges from 0.15 to 1.34. The scaling law between M(subscript o) and f(subscript c) is: M(subscript o) ~ f(subscript c)^(-3.65).
Highlights
The seismic-wave energy, Es, and seismic moment, Mo, are two commonly used parameters quantifying earthquakes and can be directly measured from seismograms
Site amplification and finite frequency bandwidth limitation both influence the measures of scaled energy i.e., the ratio of seismic radiated energy to seismic moment, and the influence is larger for the former than for the latter
The values of Es measured from the S-waves of local seismograms are larger than those calculated from the GutenbergRichter’s energy-magnitude law
Summary
The seismic-wave energy, Es, and seismic moment, Mo, are two commonly used parameters quantifying earthquakes and can be directly measured from seismograms. Several factors could affect the measures of Es and Mo from local, regional, and teleseismic data, resulting in high divergence of Es/Mo (Vassiliou and Kanamori 1982; Kikuchi and Fukao 1988; Choy and Boatwright 1995). Kikuchi and Fukao (1988) stated that the value of Es/Mo is confined to a narrow range of 10-6 - 10-5, with an average of ~5.0 ́ 10-6. They stressed that during an earthquake rupture energy loss due to cohesion cannot be ignored.
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