| 講演要旨(和文) | | 2018年北海道胆振東部地震は，厚さ数km以上になる新第三紀〜第四紀の堆積層が堆積する石狩・勇払平野の東縁で発生した．この厚い堆積層の強震動への影響を評価するため，地表／地中スペクトル比とレシーバー関数法を用いて，KiK-net観測点の速度構造を推定した．地表〜地中地震計間の構造は地表／地中スペクトル比のフィッティングにより推定した．地中地震計以深の深部構造はレシーバー関数法により推定した．地震基盤の深さは，平野内では概ね5〜8kmで，山地の観測点では2〜3kmと推定された．同地点で行われた微動アレー探査の位相速度は，高周波数側では本検討の構造モデルから計算される位相速度と良く対応した．低周波数側では，1次モードと対応するものがあった． |
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| | 講演要旨(英文) | | 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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