Seismic wavefield imaging of long‐period ground motion in the Tokyo metropolitan area, Japan

Abstract

Long‐period ground motions due to large earthquakes can cause devastating disasters, especially in urbanized areas located on sedimentary basins. To assess and mitigate such damage, it is essential to rapidly evaluate seismic hazards for infrastructures, which can be simulated by seismic response analyses that use waveforms at the base of each infrastructure as an input ground motion. The present study reconstructs the seismic wavefield in the Tokyo metropolitan area located on the Kanto sedimentary basin, Japan, from seismograms of the Metropolitan Seismic Observation network. The obtained wavefield fully explains the observed waveforms in the frequency band of 0.10–0.20 Hz. This is attributed to the seismic wavefield imaging technique proposed by Kano et al. (2017), which implements the replica exchange Monte Carlo method to simultaneously estimate model parameters related to the subsurface structure and source information. Further investigation shows that the reconstructed seismic wavefield lower than 0.30 Hz is of high quality in terms of variance reduction, which quantifies a misfit in waveforms but that the variance reduction rapidly worsens in higher frequencies. Meanwhile, the velocity response spectra show good agreement with observations up to 0.90 Hz in terms of the combined goodness of fit, which is a measure of misfit in the velocity response spectra. Inputting the reconstructed wavefield into seismic response analyses, we can rapidly assess the overall damage to infrastructures immediately after a large earthquake.

Observations and Modeling of Long‐Period Ground‐Motion Amplification Across Northeast China

“…increase amplitudes and durations of ground shaking from moderate to large earthquakes. Similar basin resonance effects have been widely documented in other sedimentary basins (e.g., Borcherdt, 1970;Frankel et al, 2009;Galetzka et al, 2015;Kano et al, 2017;Olsen et al, 2006;Pratt et al, 2017). Here we emphasize that surface waves are amplified differently compared to vertically incident shear waves, as indicated by both the observed and predicted site amplifications.…”

“…Similar basin resonance effects have been widely documented in other sedimentary basins (e.g., Borcherdt, 1970;Frankel et al, 2009;Galetzka et al, 2015;Kano et al, 2017;Olsen et al, 2006;Pratt et al, 2017). Similar basin resonance effects have been widely documented in other sedimentary basins (e.g., Borcherdt, 1970;Frankel et al, 2009;Galetzka et al, 2015;Kano et al, 2017;Olsen et al, 2006;Pratt et al, 2017).…”

“…Basin resonances are well-recognized seismic hazards, which can significantly amplify and prolong long-period (< 1 Hz) ground motions from moderate to large regional events (e.g., Asano et al, 2016;Borcherdt, 1970;Galetzka et al, 2015) and thus potentially cause devastating damage to large manmade constructions, for example, high-rise buildings, large-storage oil tanks, and long-span bridges (Hatayama, 2008;Kano et al, 2017;Pratt et al, 2017). Usually, the seismic response of sedimentary basins from large shallow earthquakes is dominated by surface waves.…”

Early Forecast of Long‐Period Ground Motions via Data Assimilation of Observed Ground Motions and Wave Propagation Simulations

“…Therefore, future data assimilation studies should also focus on structural revisions of the model by analyzing waveform records from much denser seismic network such as MeSO-net deployed in the Kanto Basin (Kano, Nagao, Ishikawa, et al, 2017;Kano, Nagao, Nagata, et al, 2017). Therefore, future data assimilation studies should also focus on structural revisions of the model by analyzing waveform records from much denser seismic network such as MeSO-net deployed in the Kanto Basin (Kano, Nagao, Ishikawa, et al, 2017;Kano, Nagao, Nagata, et al, 2017).…”

“…The reliability of a forecast strongly depends on the resolution of the subsurface structure model used in the 3-D FDM simulation. Therefore, future data assimilation studies should also focus on structural revisions of the model by analyzing waveform records from much denser seismic network such as MeSO-net deployed in the Kanto Basin (Kano, Nagao, Ishikawa, et al, 2017;Kano, Nagao, Nagata, et al, 2017).…”