Effect of Finite Frequency Bandwidth Limitation on Evaluations of Seismic Radiation Energy of the 1999 Chi-Chi Earthquake

Abstract

Based on the ω−2 and ω−3 source models, we explore the effect on estimates of seismic radiation energy, Es , caused by finite frequency bandwidth limitation of source spectra. Let fc be the corner frequency of a source spectrum and fu and fc are, respectively, the upper and lower bounds of a frequency band in use. Results show that the effect depends on fu/fc and fl/fc , and Es is under-estimated when fl > 0 and fu < ∞. When fu/fc < 20, the effect is sensitive to both fl/fc and fu/fc for the ω−2 source model, but mainly to fl/fc for the ω−3 model. When fu/fc > 20, the effect is insensitive only to fu/fc for the two models. Let Es' be the seismic radiation energy estimated without removal of finite frequency bandwidth limitation. Results show: (1) Es'/Es first slightly increases and then decreases with increasing fc ; or (2) Es'/Es monotonously decrease with increasing fc. For the 1999 Ms 7.6 Chi-Chi earthquake, Taiwan, Es was under-estimated by Hwang et al. (2001), and the degree of under-estimates varies from station to station.

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