Empirical Estimation of Long-Period (1-10 Sec.) Earthquake Ground Motion on Hard Rocks

Abstract eng:
As a basic approach to understand long-period (1-10 sec.) ground motion (LPGM), we obtained a spectral LPGM attenuation model on hard rocks using the downhole data registered by the KiK-net (NIED) hard rock sites of which S-wave velocity exceeds 2.0 km/s. The data from earthquakes of larger magnitudes than 5.9 were used. Next, we estimated the shakeability at arbitrary sites using K-NET and KiK-net surface recordings by taking spectral ratio to the proposed model for hard rocks. A very strong spatial variation of shakeability was found in and around large basins. The shakeability at thick sediment sites exceeding more than 10 times of rock sites is not rare and it also depends strongly on period. The obtained shakeability may be useful for assessing seismic safety of long-period structures. To use the average with one standard deviation is recommended as a standard predictive model for hard rock sites. In addition, site amplifications by including one standard deviation with the average are recommended for safer consideration of LPGM.

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