Constructive Intereference of Long-Period Seismic Waves in Horizontal Plane in Urbanized Area During 2011 Tohoku Earthquake in Japan

Abstract eng:
The anomalous amplification of the long-period ground motions in the Osaka and Ise Bay areas in the western part of mainland Japan during the 2011 Tohoku earthquake was investigated in this study. One of the most symbolic phenomena during the 2011 Tohoku earthquake was the strong motion recorded at the top of a 55-story steel office building located in the Osaka Bay area more than 700 km away from the epicenter and the damage to the inside of the building. The top of the building experienced large drift, and the records indicate one-sided displacement exceeding 1.3 m, which is the largest disclosed displacement of any super high-rise building in Japan. This can only be explained by the targeted amplification of the long-period ground motions within the sedimentary layers of the Osaka Basin. Similar site amplification was also observed in the Ise Bay area. The contours of the peak values of the pseudo velocity response spectra with a 5% damping factor in the Osaka and Nobi Plain areas indicate the local anomalous amplification of long-period ground motions with a predominant period of 6–7 s at coastal sites. To elucidate the interference mechanism of the long-period seismic waves in the Osaka and Nobi Plains, the threedimensional (3D) finite difference method was used for wave propagation analysis incorporating an arbitrarily heterogeneous geologic structure. This method requires a large amount of computational time and storage to simultaneously consider the rupture of the seismic faults for the 2011 Tohoku earthquake and geologically model the Osaka and Nobi Plains. Therefore, the sedimentary basin-like structure of the Osaka and Nobi Plains is considered assuming the incident wave field from the epicenter of the 2011 Tohoku earthquake. The ground motions recorded at sites in the Osaka and Nobi Plains during the 2011 Tohoku earthquake were well reproduced by the 3D calculations. The agreement between the observed and calculated ground motions at the coastal sites indicates that the large amplification of the ground motions was caused by the 3D effect of the wave interference in the complex subsurface structure of the Osaka and Nobi Plains. This paper focuses on the amplification mechanism of long-period ground motions in the Osaka Plain. The 3D effect of the ground motion amplification in the Osaka Plain was compared with the 2D model results using soil responses at horizontally arrayed sites under Ricker wavelet incidence. At sites in the Osaka Bay area, the peak amplitudes of 3D response waveforms and their Fourier amplitude were larger than those of the 2D response. Snapshots of the wave components reveal that the third pulse has a distinctive amplitude because of the constructive interference of the multiple passing waves in the 3D structure. The amplification area was small and limited partly by the concentration of the multiple passing waves in the Osaka Bay area.

• Export as: BibTeX | MARC | MARCXML | DC | EndNote | NLM | RefWorks
• Add to your basket