| dc.description.abstract |
Strong ground motion parameters (κ0、Q、Mw、M0 and △σ) were measured from seismograms of Taiwan Strong Motion Instrument Program (TSMIP) with local magnitudes (ML) between 3.0–7.1 that occurred between 1993 and 2014 in this study. Meanwhile, inversion technique was also used for testing input for stochastic simulation method.
First, the high frequency decay parameter, kappa (κ) was computed by fitting the Fourier amplitude spectra of each station from TSMIP network. The relation between κ values and the hypocentral distance (Rhyp) were calculated from SH-waves for each individual station. Incidentally, the κ value at Rhyp=0 (denoted as κ0) can be used as site parameter, the range of κ0 for TSMIP stations were from 0.0185 - 0.0939 s in this study and the distribution is highly corresponding to geology and velocity. For instance, low κ0 values that below 0.06 s were occurred in and around the Central Mountain and foothill region, which was basically located in the middle of Taiwan. In contrast, high κ0 values that upon 0.06 s were observed at the alluvial areas, i.e., the Taipei basin and the Ilan plain in the northern Taiwan, the Chianan plain in the southwestern Taiwan, and the longitudinal valley in the eastern Taiwan. The site-specific κ0 values from 426 stations were correlated with the averaged shear wave velocity of the top 30 m of strata (VS30), and the relationship could be described by κ0 =0.163 – 0.077·ln(VS30) ± 0.053 and a high linear correlation (R2 = 0.63) was found.
The second part, the generalized inversion technique (GIT) (Oth et al., 2011) was used for inversion purpose of seimogenic parameters from SH-wave in the frequency range 0.1 to 40 Hz (interval 0.1 Hz) for whole Taiwan region (Taiwan model) and the southern region (regional model). The attenuation characteristics, earthquake source parameters and site amplification functions could be decomposed step by step from GIT. In this study, the characteristics of the site amplification are referred to horizontal-to-vertical (H/V) Fourier spectral ratios of earthquakes for a referent rock site. The basic three effects were are set with the parameters of Boore (2003) to determine the rest seismic moment(M0)、corner frequency(fc)、stress drop(△σ) and Q(f).
Finally, the strong ground parameters obtained by this study are verified from stochastic simulation method. Accordingly to size of seismic source, point source technique (SMSIM) was used for ML<6 and finite-fault technique (EXSIM) with correlated source information (fault plane solution and slip, etc.) was used for ML≧6 events. However, the definition of κ0 obtained from this study is differed from that of previous studies (Boore, 2003; Boore, 2009, SMSIM and EXSIM). Several changes were made in this study, first, the κ0 and site amplification were exclude from waveforms that were generated from SMSIM. Second, different shape of high-frequency decay (related to κ0) spectrum generated from this study and also site amplification function was superposed in the SMSIM simulation spectrum in frequency domain. Finally, the regional parametric model was used to obtain the best simulation results for SMSIM technique. However, if there is no regional parameter model, Taiwan model can also get a good simulation results. When source information could be found for large earthquakes, EXSIM could provide better simulation results. Therefore, the parameters model calibrated in this study can be used to predict ground motion. | en_US |