| 講演要旨(和文) | | 大都市の地下に伏在する断層を調査するために，人工信号源を用いる電磁探査法（CSMT法）を改良し，大都市域での電磁気高雑音地域でも実施可能な電磁探査法を開発した。この装置はGPSを用いた送受信装置間の時刻同期により，高い信号検出能力を有するものであり，開発した装置を大阪平野の都市域に伏在する上町断層の調査へ応用した。調査では，送信源は大和川に，受信点は送信源から北に約15km 離れた淀川長柄橋付近に設け，送信信号が受信点に到達していることを周波数分析により確認して，上町断層を横切る深度800mまでの比抵抗断面を得た。その比抵抗断面は，先行研究の反射法地震探査断面とも整合的であり，東傾斜の上町断層を比抵抗という物理量で描出できた。また，東側の深さ400m以深は高比抵抗となり，東側の花崗岩類の基盤が西側より浅いことを明らかにした。 |
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| | 講演要旨(英文) | | We newly developed a CSMT equipment to explore a concealed fault under a big city with a high amount of electromagnetic noise. The instrument realized high signal detection capability by synchronizing data sampling between the transmitter and receiver by using GPS. This equipment was applied to investigate the Uemachi fault, a concealed fault under Osaka city. The signal source was installed at Yamato-gawa. Receiving points were set up near Yodogawa Nagara-Bashi, which is about 15 km away from the signal source and to its north. The transmitted signal reached the receiving points was checked by conducting the frequency analysis of the received waveforms. The resistivity section across the Uemachi fault was obtained up to a depth of about 800m. The resistivity section is well correlated with the seismic reflection profile obtained in a previous study. It shows a high-resistivity zone inclining northeast in the region where the fault is presumed to be located. There is a high-resistivity region to the northeast of the fault. The former high-resistivity zone coincides with the flexure zone of the Uemachi fault. The latter zone coincides with the granitic rocks as the basement rock to the Osaka Group, indicating that the basement rocks in the northeast site of the fault are shallower than the southwest side. |
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