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| | Abstract | | The 2018 Hokkaido Eastern Iburi earthquake occurred at the southeastern part of the Ishikari and Yufutsu plains that have thick (> few km) Neogene-Quaternary sediments. In order to investigate effect of the thick sediments to the strong motion, we estimated velocity structure below KiK-net seismic stations by using surface-to-borehole spectra and receiver function method. Shallow structure between the surface and borehole seismometer depth were estimated from fitting of surface-to-borehole spectral ratio. Deep structure between borehole seismometer and seismic bedrock were inferred from receiver function analysis. The estimated depths of seismic bedrock were approximately 5 to 8 km for the sediment sites, but were about 2 to 3 km for the mountain sites. Phase velocities calculated from the estimated velocity structure were consistent with the ones obtained from SPAC microtremor observations in the higher frequencies. In the lower frequencies, phase velocities of the SPAC observations correspond to ones of the first higher mode of Rayleigh wave. |
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