| Summary: | 碩士 === 國立中央大學 === 地球科學學系 === 102 === The 1909 Taipei earthquake (M6.8) occurred beneath the Taipei Metropolitan Area (TMA), the possible seismic hazard similar to the 1909 Taipei earthquake would require special attention. According to the hypocenter relocated from historical archived travel times of the 1909 Taipei earthquake by Kanamori et. al (2012), we simulated ground motions in TMA by using Spectral Element Method (SEM). A 3D velocity structure with topography and sediment layers in Taipei basin was also included in the simulation.
As the results of point-source simulations, the tension type mechanism may cause larger ground motions than the subduction zone type mechanism. The higher peak-ground-motion values occurred in the western part of Taipei basin with both two types of focal mechanisms. This distribution might correspond to the thicker sediment layers in the western part of the basin. The finite fault simulation showed that the high PGV area spread wider than the results from point-source assumption, and the coda waves became more obvious and caused longer shaking duration at station TAP than point-source assumption with the same focal mechanism.
SEM could provide us good prediction of low frequency ground motions, however, for real earthquakes, waveforms consist of broad frequency band signals. In order to obtain the information in a broad frequency band we simulated waveforms with hybrid method, which is a combination of SEM and empirical Green’s function method (EGFM). For higher frequency components, we chose a recently happened deep event (2013/10/11 M4.9 Depth:143.8 km) in Taipei area as the empirical Green’s function for the 1909 Taipei earthquake. We corrected the amplitude of the broadband records with hypocentral distance from depth 143.8km to 75km and modified the magnitude from ML4.9 (CWB) and Mw4.2 (RMT) to target magnitude (Mw6.8 and Mw7.3) by using EGFM. An east-dipping (δ=344°, λ=57°, φ=103°) finite fault was considered in the SEM simulation to obtain the lower frequency components. We also moved the hypocenter to the relocated hypocenter from Kanamori et al. (2012) and simulated both higher and lower frequency components.
By combining the time series of lower (SEM) and higher (EGFM) frequency components, the model of modifying the magnitude from Mw4.2 to target magnitudes (Mw6.8 and Mw7.3) has more reasonable PGA values and response spectra curves than from ML4.9 to target magnitude (Mw6.8 and Mw7.3). The observed PGA values from literature are 59.3 gal at station TAP and 67.0 gal at station KEE. According to the simulation results, the PGA values (TAPB/TAP：59.9 gal；WSFB/KEE：140.4 gal) from the model with target magnitude Mw7.3 and higher stress drop are closest to the observed values. For the analysis of strong shaking durations and PGA values, the station inside Taipei basin (TAPB) has lower PGA values but longer strong shaking durations.
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