Analysis of amplified ground motion in Bangkok from recent earthquakes (2023)

Summary

The horizontal elastic response spectrum of earthquake ground shaking recorded at TMDA recorded from all six considered events in Table 2 from 2007 to 2016 are displayed in Fig. 8. The thick black lines show the pseudo-spectral acceleration of TMDA (surface) while the thick black dash lines show horizontal elastic response spectra of TMDB (borehole) for the RotD50 component of horizontal SA directions. In addition, the grey lines show spectrum at SRDT and PRAC stations. It could be clearly observed that the spectrum in Bangkok is much larger than those from outside basin stations located at a similar distance for most structural periods. Furthermore, the horizontal spectra of TMDA show high energy at long periods observed between 0.5 and 2 s, similar to those reported using microtremor observations by Bidhya et al. (2021). It is interesting to note also that the amplification at spectral ordinate between 4 and 6 s could be observed from TMDB records from both 2008 and 2009 events. However, the spectral amplification at other periods, between 0.5 and 0.7 s, observed from all considered events in TMDA (surface) are missing from TMDB (borehole) spectrums. These results indicate that the top 47-m surface layer plays a key role in determining the pattern of the observed spectrum at short structural periods.Fig. 8Horizontal elastic spectral acceleration motion at TMDA (thick black line), SRDT, and PRAC (grey lines) during six events in Table 2 with 5% damping ratio. The thick dot lines show horizontal spectrum for selected windows contains only the body waves (without surface waves). The estimated median horizontal spectrum computed from Boore et al. (2014) and Zhao et al. (2006) are shown in red and green, respectively. The thick black dash lines show horizontal elastic response spectra of TMDB (borehole)In order to investigate the long period energy content within the basin, the calculated horizontal spectrum of the TMDA station using different parts of accelerogram are...