Earthquake and eruption off east Izu Peninsula.

Komiya, Manabu

doi:10.5026/jgeography.99.123

Cited by 2 publications

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“…These occurrences were in 1870, 1930, and from 1978 to 1989. In the twelve-year period of the latest activity, the Japan Meteorological Agency observed 12 earthquake swarms (Komiya, 1990). On June 30, 1989, an earthquake swarm began late in the day.…”

Section: Introductionmentioning

confidence: 99%

“…This was caused by right-slip motion along a fault (RF in Fig. 1), (Komiya, 1990;Tada and Hashimoto, 1989). Seismic activity decreased after the main shock and the number of earthquakes, measured in three-hour periods, decreased to less than 50 by July 11th.…”

Section: Introductionmentioning

confidence: 99%

“…From 20h 38m of July 11, seismometer at Kamata station began to record tremors with large amplitudes. Several periods of these large-amplitude tremors were recorded from July 11 to 13 (Komiya, 1990).…”

Section: Introductionmentioning

confidence: 99%

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Birth of a Submarine Volcano "Teisi Knoll".

Oshima¹,

Tsuchide²,

Kato³

et al. 1991

J,Phys,Earth

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Frequent sea bottom surveying in an area of earthquake swarms in Sagami Bay about 2 to 3km from the east coast of Izu Peninsula clearly disclosed the birth of a new submarine volcano and processes of its formation. Bathymetric soundings, taken on July 9, 1989, showed that the seafloor, where the new volcano was to be born, was characterized by undeformed sedimented bottom in depths of about 100m. Large-amplitude tremors, beginning on the evening of July 11, were associated with the formation of a new volcanic knoll (cryptodome). This was confirmed by the survey vessel "Takuyo" on July 13 at 18 h 28m when it was found that the knoll had risen 25m above the surrounding seafloor. Five minutes later, after the existence of this newly formed bulge was established, a submarine eruption from the knoll began. While escaping from the hazardous area, Takuyo took photographs and made video tape recordings of the effects of the eruption on the sea surface and in the atmosphere. In addition, audio records of a series of frightening acoustic shocks of the volcanic activity were made. These shocks suggest frequent discharges from the seafloor of high pressure gasses associated with sub-bottom phreatomagmatic eruptions. On July 15, an unmanned automated survey craft, the Manbou, recorded a column of gas bubbles rising from the 200m diameter crater in the center of the knoll. The eruption of July 13 had lowered the height of the dome from 25 to 10m. Three months later a detailed bathymetric survey, using a highly accurate multibeam sounding system, Hydrochart, confirmed the maar-like topography of the volcano and also recorded the weakened emission of gasses.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Birth of a Submarine Volcano "Teisi Knoll".

Oshima¹,

Tsuchide²,

Kato³

et al. 1991

J,Phys,Earth

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Undersea Seismic Observation of 1989 Volcano-Seismic Activity, off Ito, Izu Peninsula, Central Japan.

et al. 1991

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Volcano-related seismicity associated with the July 13, 1989, submarine eruption off Ito, Izu Peninsula, central Japan, began with a swarm activity on June 30. Two ocean bottom seismometers (OBSs) deployed near the future eruptive vent observed several precursor explosive activities during the two days preceding the surface eruption. OBS records show precursor waveforms, called "spindle packets," which resemble those during the surface eruption. After the eruption, a sonobuoy was repeatedly deployed above the vent and, finally a cable OBS was deployed 1km NW of the vent. Isolated volcanic explosions show high frequency sound arrivals and low frequency (1.2Hz) coda on the vertical seismometer; this coda, which has a group velocity of approximately 330m/s, is identified as a Rayleigh wave. The high frequency arrivals result from the propagation of sound waves through the water column. Hypocenters before the surface eruption trended WNW-ESE and had depths between the ocean bottom and 6km. After the eruption, earthquakes occurred around the vent with depths a few kilometers below the surface.Sonobuoy records show an X phase. Assuming the X phase is generated by the conversion of an S wave to a P wave at the magma surface, the depth to the top of the magma is estimated as 1km below the hypocenter. Quiet vent site hydrothermal activity was observed one and half months after the surface eruption. Although rising bubbles were seen, no earthquake was located beneath the vent site.

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Earthquake and eruption off east Izu Peninsula.

Cited by 2 publications

References 0 publications

Birth of a Submarine Volcano "Teisi Knoll".

Birth of a Submarine Volcano "Teisi Knoll".

Undersea Seismic Observation of 1989 Volcano-Seismic Activity, off Ito, Izu Peninsula, Central Japan.

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