Publication Date:
2021-05-19
Description:
In response to the eruption of Miyake-jima volcano starting in June 27, 2000 and the associated
swarm earthquakes in the west of lvliyake-jima island, the comprehensive surveys and ocean
bottom earthquake observation were conducted by the Japanese Hydrographic Department. Some of
the survey results and the derived sub-bottom structure were presented with consideration of
teetonics as to the northern part of the Zenisu ridge inferred from geophysical data of topography,
magnetic and gravity anomalies covering the northern part of the Izu-shoto region The narrow
multi-beam soundings in the west of the Miyake-jima island show the small volcanic cones in the
southeast offing of the Kozu sluma island The seismic records proved the existence of many normal
faults segmenting the sedimentary layers, which may imply the compressive stress field in
NW-SE direction. It is also confirmed that the swarm earthquake region coincides well with the
northeastern edge of magnetic basement high. Magnetic basement highs implying the dyke intru
sion were also recognized between the Nii-jima and Kozu-shima islands. These features may suggest
upwelling of magma through NW SE trending deep fractures caused by regional stress field.
The general distribution of magnetic and gravity anomalies covering the northern part of the Izu
shoto region, show the good correspondence with the tectonic lines mferred from seismic activity
The northern part of the Zenisu ridge has been segmented into three part, Omurodashi ,Ni i jima,
and Kozu-shima blocks, and in between there exist magnetic basement highs implying the dyke
mtrusion thiough the deep fractures in the crust.
The deflection of the major axis of Nii-jima islands is ascribed to the rotational movement caused
by the huge dyke intrusions occurred in the east of the island.
Description:
Published
Repository Name:
AquaDocs
Type:
Journal Contribution
,
Refereed
Format:
pp. 37-56
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