Marine Ecosystems Research Department - jamstec japan agency ...

Japan Marine Science and Technology Center
Deep Sea Research Department
(Figure ). A larger scale electromagnetic survey was
made using ocean bottom electromagnetometers to
obtain mantle electric conductivity distribution (Figure
). In order to obtain a similar scale seismological
structure, the next survey aims to record natural earthquake
signals, which will be carried out in -.
2. Observation Networks on Deep Sea Floor
a) Development of sea floor earthquake observation
systems
JAMSTEC has continued to operate major fiber
optic cabled observation systems south off Muroto of
Shikoku Island over the Nankai Trough forearc
(a)
(b)
N
20˚
19˚
18˚
17˚
16˚
15˚
14˚
140˚
141˚
142˚ 143˚ 144˚ 145˚ 146˚ 147˚ 148˚ 149˚ E
-10000 -8000 -6000 -5000 -4000 -3000 -2000 -1000 0
Fig. 3 (a) Map of the experimental area. A main seismic line shown by a blue line runs from the eastern end of the forearc region
to the Parece Vela basin through the Mariana arc and trough. An airgun shooting by R/V Kaiyo was limited from the eastern
end of the line to OBS#45 due to bad weather from an unexpected typhoon. We deployed 106 OBSs as shown by open
circles. All OBSs ware recovered, but six OBSs data shown by black circles were unavailable due to recorder troubles. Red
stars indicate long term OBSs retrieved during KY03-01 cruise. Contour interval is 500 m. (b) Preliminary seismic velocity
structure model obtained by the OBS experiment. Contour interval is 0.1km/s. We imaged variations of the crustal thickness
and the velocity structure. The upper figure is from forward modeling, and the lower figure from inversion using first
arrivals. The white broken line is the estimated Moho.
(a)
(b)
Site 8
Site 9
(East Mariana Trough) (Mariana Islands)
0
FLX2
(Forearc)
Depth (km)
50
100
150
200
-100 -50 0
50 100 150
Distance (km)
Ohm-m
10 5
10 4
10 3
10 2
10 1
10 0
Fig. 4 (a) Large scale electric conductivity experiment using
OBEM (ocean bottom electro-magnetometers). (b)
Two-dimensional electrical conductivity model beneath
the red rectangle in (a). White broken line is the top of
the subducting Pacific Plate inferred from seismicity.
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