Impact of topography and near-surface layers on ground motion: a finite difference study of the 2011 Tohoku earthquake
摘要
The 2011 Tohoku earthquake (Mw 9.0) took place in the Northeast Japan (Tohoku) forearc area in a megathrust zone and struck off the Pacific coast of Tohoku. The structural damage was observed in various regions, mostly caused by the ground motion characteristics of the local site. This study investigates the influence of topography and near-surface velocity layers on seismic ground motion, using the 2011 Tohoku earthquake (Mw 9.0) as a case study. The horizontally polarized shear wave (SH) propagation has been modeled using a staggered grid finite difference method (FDM) with 12th-order spatial and second-order temporal differentiation. The computer code-named MSH2DEMEE in FORTRAN language has been used for finite difference modeling. The strong motion data from the KiK-net network, featuring borehole and surface records, enabled detailed analysis of near-surface effects. The significant amplification of ground motion has been observed with amplification factors ranging from 2 to 7 as SH waves travel from borehole to surface. The comparison between observed and simulated records demonstrated a strong correlation in peak ground acceleration (PGA) and response spectra which confirms the validity of the methodology. The effectiveness of MSH2DEMEE is firmly proven by the comparison of the root mean square error of waveforms. This study emphasizes the significant impact of local site effects, such as topographic variations, on seismic response and demonstrate the effectiveness of FDM in modeling realistic ground motion for seismic hazard assessment and earthquake-resistant design.