Abstract

We apply seismic interferometry based on deconvolution to earthquake data observed in a building at Tokyo Metropolitan University to extract building response and estimate velocities and frequencies of traveling waves inside the building. The building is a 10‐story reinforced concrete structure in Tokyo, Japan. The earthquake data were recorded 2 months before, 6 months after, and 16 months after the Mw 9.0 Tohoku‐Oki earthquake (11 March 2011). The observation period of each acquisition was 20–30 days. We analyze more than 300 earthquakes recorded in these time periods, and we find significant reduction (∼20%) in wave velocities and fundamental‐mode frequencies after the Tohoku‐Oki earthquake. Because deconvolution interferometry separates the response of the building from the effect of complicated wave propagation outside the building, we interpret that this reduction is mostly related to the building. We can also estimate frequencies of the fundamental mode from observed data, and these frequencies contain the responses of building and the ray paths from hypocenters. Therefore, as we find from the data, the frequencies estimated from observed data are generally lower than those from deconvolved waveforms due to the effects of wave propagation. Although the velocities in the building decrease ∼20% after the Tohoku‐Oki earthquake, we cannot find significant reduction in the S‐wave velocities at the near surface (depth shallower than 100 m). This fact indicates the decrease in velocities is mainly related to the building, and hence, with deconvolution interferometry, we can detect damages to the building caused by the Tohoku‐Oki earthquake.

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