Earthquake Magnitudes Based on Coda-Derived Source Spectra in Taiwan

• Main Authors: Feng-Shan Tu, 涂鳳珊
• Other Authors: 龔源成
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/55114757034282242900

碩士 === 國立臺灣大學 === 地質科學研究所 === 99 === We apply the coda-derived source spectrum method to estimate earthquake magnitudes in Taiwan. 76 events occurred during the time period from 1996 to 2010 around west-south Taiwan recorded by BATS (Broadband Array in Taiwan for Seismology) with magnitudes between Mw 3.2 and 6.21 are used in this study. From two horizontal components of waveform data, we extract the coda envelopes at 12 frequency bands between 0.05 and 8.0 Hz. We construct the synthetic coda-envelope by using various empirical distance-frequency-dependent corrections. The derived synthetic coda envelops are compared to the observed coda-envelope to evaluate the dimensionless coda amplitudes. With further considerations on path effects, site effects and source-to-coda transfer functions, the dimensionless coda amplitudes at each frequency band are used to construct the source spectra, which is then used to determine the earthquake magnitudes. The 76 derived coda-magnitudes (MC) are consistent with corresponding moment magnitudes (Mw). Our result also shows the overall deviations between MC and local magnitude (ML) reported from Central Weather Bureau are less than those between Mw and ML. While the implications need further investigation, the results indicate that the broad-band coda information does reconcile, to some extent, the long-lasting discrepancy between the low frequency magnitude (Mw) and the high frequency magnitude (ML) in Taiwan. Moreover, we found out that there is a very stable linear relationship between coda-derived source amplitudes at 2.5 Hz and the ML scale, implying that the source information is well maintained by the high-frequency coda, and this property shows it is potentially very feasible to extend this method to smaller earthquakes in Taiwan.