| 講演要旨(和文) | | 2016年熊本地震の発生時には、布田川断層帯東部の布田川区間において地表に地震断層が現れており、余震活動も盛んであったことが知られている。一方、同じ布田川断層帯西部の宇土半島北岸区間では、断層変位はみられず、余震活動も活発ではない。このため、この区間での将来の地震発生や、それに伴う強振動と大きな地表変位が懸念されている。そこで、宇土半島において行われたAMT探査データを解析し、宇土区間での浅部比抵抗構造を推定した。その結果、活断層沿いに低比抵抗帯が分布することが明らかとなった。この低比抵抗帯の規模は、布田川区間と比べて小規模であった。このことから、宇土半島北岸区間では布田川断層の活動は盛んではなく、地表付近まで地震断層が達する可能性も低いことが推測できた。 |
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| | 講演要旨(英文) | | At occurrence of the 2016 Kumamoto earthquake, the large ruptures appeared on the ground surface along the eastern part of Futagawa fault zone, called as the Futagawa segment. The aftershock activity was also high along the segment. On the other hand, the western part of Futagawa fault zone, called as the Uto Peninsula north-coast segments, has no fault displacement at the earthquake and no aftershock activities. This feature implies that the western segment still has the risk of future earthquakes with strong shakings and large surface displacement. Therefore, we analyzed audio-frequency magnetotelluric data obtained in the Uto Peninsula, and estimated the shallow resistivity structure across the Kamiouda fault, a part of Uto Peninsula north-coast segments. We found a low resistivity zone distributed along the active fault, interpreted as sub-surface damaged zone with a large amount of pore water. It is also found that the spatial scale of the low resistivity zone is smaller than ones along the Futagawa segments, having a obvious surface ruptures at the Kumamoto earthquake. As conclusion, we infer that the activity of the Uto Peninsula north-coast segments is not high, and the possibility of the surface rupture at future earthquake will low. |
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