Ocean Bottom Seismographic Observation at Minami-Hiyoshi Seamount at the Northern End of the Mariana Arc
Minami-Hiyoshi Seamount is located at 1,400 km south of Tokyo, Japan, and it is one of the submarine volcanoes on the volcanic front of the northern Mariana arc. The seamount is also called Hiyoshi-okinoba. Submarine eruption was detected on Aug. 25, 1975 and widespread discolored water phenomenon was observed in 1977. Discolored water phenomena were observed in 1992 and 1996, too. No indications of the submarine eruption were detected since then. We carried out several geophysical surveys to elucidate the present seismic and volcanic activity of Minami-Hiyoshi Seamount in Aug.-Sep. 2001. We deployed nine OBSs on and around MinamiHiyoshi Seamount. Four airgun profiles with lengths of 50-70 km were surveyed. The obtained crustal model shows P wavespeeds are higher just beneath the summit than those around the seamount. The existence of low wavespeed materials was suggested at depths around 6 km beneath the seamount. The seismicity around Minami-Hiyoshi Seamount was low during the observation period from Aug. 4 to Sep. 11, 2001. However, many very small seismic events were detected by the only OBS deployed at the summit of the seamount. Most of the determined hypocenters were located outside of the OBS array and they were distributed near Nikko Seamount located at 60 km southeast from Minami-Hiyoshi Seamount.
| Main Authors: | , , , , |
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| Format: | Journal Contribution biblioteca |
| Language: | Japanese |
| Published: |
2003
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| Online Access: | http://hdl.handle.net/1834/15735 |
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| Summary: | Minami-Hiyoshi Seamount is located at 1,400 km south of Tokyo, Japan, and it is one of the submarine volcanoes on the volcanic front of the northern Mariana arc. The seamount is also called Hiyoshi-okinoba. Submarine eruption was detected on Aug. 25, 1975 and widespread discolored water phenomenon was observed in 1977. Discolored water phenomena were observed in 1992 and 1996, too. No indications of the submarine eruption were detected since then. We carried out several geophysical surveys to elucidate the present seismic and volcanic activity of Minami-Hiyoshi Seamount in Aug.-Sep. 2001. We deployed nine OBSs on and around MinamiHiyoshi Seamount. Four airgun profiles with lengths of 50-70 km were surveyed. The obtained crustal model shows P wavespeeds are higher just beneath the summit than those around the seamount. The existence of low wavespeed materials was suggested at depths around 6 km beneath the seamount. The seismicity around Minami-Hiyoshi Seamount was low during the observation period from Aug. 4 to Sep. 11, 2001. However, many very small seismic events were detected by the only OBS deployed at the summit of the seamount. Most of the determined hypocenters were located outside of the OBS array and they were distributed near Nikko Seamount located at 60 km southeast from Minami-Hiyoshi Seamount. |
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