| dc.description.abstract | The seismic radiated energy, Es, and seismic moment, Mo, are two fundamental parameters of an earthquake. The scaled energy, Es/Mo, is defined to be the ratio of seismic radiated energy to seismic moment, denotes the radiated energy per unit seismic moment of an earthquake. Several factors could affect the measures of Es and Mo from local, regional, and teleseismic data, thus, resulting in high divergence of Es/Mo. The strong site effect, especially at higher frequencies, can produce an over-estimates of source parameters; while finite frequency bandwidth limitation leads to an opposite effect.
Based on the quarter-wavelength approximation method proposed by Boore and Joyner (1997), the site amplifications at 87 strong-motion stations in central Taiwan are evaluated from the velocity and density structures constructed from well-logging data in the topmost 30-m and 3D velocity models inferred from earthquake data.
In addition, the formulas used to eliminate the effects on Es, Mo, and Es/Mo caused by finite frequency bandwidth limitation based on the w-squared source model are presented.
In this study, we measure the values of Es and Mo for 22 aftershocks with 5.1£ML£6.8 of the 1999, Chi-Chi, Taiwan earthquake based on the local seismograms from the Central Weather Bureau. The method proposed by Andrew (1986) is used. After the corrections, i.e., the radiation pattern, free surface amplification, Q-factor, the site effects, and finite frequency bandwidth limitations, the results are Es=2.0´1018 – 8.9´1021 ergs and Mo=1.3´1023 – 1.4´1026 dyne-cm. This gives Es/Mo=7.4´10-6 – 2.6´10-4, with an average of ~7.9´10-5. Es/Mo slightly increase with earthquake magnitude. The Mo – fc scaling almost has the following relation: Mo~fc-3.65. In addition, Es/Mo slightly depends on the depth in the following form: Es/Mo=1.92´10-5e0.09h, where h is focal depth. | en_US |