Explaining Extreme Ground Motion in Osaka Basin during the 2011 Tohoku Earthquake
Despite being 770 km away from the epicenter, observed ground motions due to the Tohoku earthquake in the Osaka Basin were unexpectedly large, with an amplification of more than a factor of 20 compared to immediately outside the basin, and including 2.7 m peak-to-peak roof displacements at one high-rise building. The local ground motions exceeded expectations based on standard computations of site response by a factor of 3, predicted frequencies of peak acceleration were off by at least 50%, and such discrepancies have not yet been explained quantitatively. Here we show that utilizing semianalytic theory for surface-wave amplification, we are able to accurately predict both the amplitudes and frequencies of large ground amplification in the Osaka Basin using only knowledge of the local one-dimensional structure. Comparison between this simple prediction and observed amplification was not expected to be so favorable and suggests that simple one-dimensional surface-wave site amplification factors can be useful in the absence of full three-dimensional wave propagation simulations. Such surface-wave amplification factors can be included in addition to the standard measures of site-specific site amplification and should help explain strong ground motion variability in future large earthquakes that shake Osaka Basin and elsewhere in the world.
Additional Information© 2017 American Geophysical Union. Received 10 MAY 2017; Accepted 18 JUL 2017; Accepted article online 20 JUL 2017; Published online 30 JUL 2017. We thank T. Furumura and two anonymous reviewers for comments that helped improve the manuscript. The KiK-net data used in this study were obtained from the National Research Institute for Earth Science and Disaster Prevention (NIED) data centers, http://www.kyoshin.bosai.go.jp/kyoshin/. This work was partially supported by NSF EAR-1453263.
Published - Tsai_et_al-2017-Geophysical_Research_Letters.pdf
Supplemental Material - grl56214-sup-0001-Text_S01.docx