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| | Abstract | | The Hokusetsu area located in the northern part of the Osaka Basin, Japan, has the complicated geological structure including graben, called the Imogawa lowland, between the Hokusetsu Mountains and the Senri hill. We estimated the S-wave velocity structures in both the graben site and the hill site by carrying out microtremors array surveys with the maximum radius of around 0.1km (S-array) and 0.5km (L-array), respectively. The observed phase velocity up to 2 km/s was obtained by these microtremor array surveys. On the other hand, the estimated depth of basement rock (Vs > around 3 km/s) is not accuracy enough in the microtremor array surveys. To estimate the deep structures, therefore, we reanalyzed data of two different seismic reflection survey conducted at the Hokusetsu area and integrated the results of the microtremors array surveys and the seismic reflection surveys. As the result, the depth of basement rock of the integrated structural models is about 1km at the Imogawa lowland and about 0.6km at the Senri hill, respectively, indicating the shape inclined bedrock spread in the Hokusetsu area. |
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