Marine Ecosystems Research Department - jamstec japan agency ...

Japan Marine Science and Technology Center
Institute for Frontier Research on Earth Evolution (IFREE)
E (Fig.). This result indicates the intensities of
39˚ 00'N
39˚ 06'N
39˚ 12'N
39˚ 18'N
39˚ 24'N
reflected waves have a relation to the spatial micro-
143˚ 12'E
seismicity variations.
143˚ 18'E
143˚ 24'E
143˚ 30'E
Time (sec)
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
(sec)
39.0 39.1 39.2 39.3 39.4
Fig.20 Mapping of a strong reflector at a plate boundary off
Sanriku.
uses an algorithm like diffraction stacking method. As
a result of these analyses, we found that: (i) there is a
high velocity region corresponding to an aeromagnetic
anomaly in the shallower part of the island upper
crust, (ii) the dip of the subducting Pacific plate
changes at about . degree E, which is km eastward
of the trench axis, (iii) the uppermost oceanic
mantle has lateral velocity variations.
In the off-Sanriku region, the spatial distribution of
microearthquakes shows significant variation, even in
the north-south direction, which is parallel to the
trench axis. We succeeded in imaging the reflected
wave amplitude variation from the plate boundary on
three N-S direction survey lines around . degree
(km)
3. Seismogenic Zone Material Science Research
Group
3.1. Outline
In order to understand complicated processes in
plate dynamics, such as seismic preparation, rupture
and recovery processes along the plate boundary, the
material science subgroup conducts three research
programs: the first involves experimental studies on
frictional behavior and failure processes of plate
boundary materials, the second involves structural,
petrological, and rheological studies of past plate
boundary rocks, and the third aims to construct a theoretical
model of plate boundary dynamics involving
thermodynamics, kinetics, and rheology of the plate
boundary rocks in the subduction zone.
3.2. Results
() Plate boundary décollement zone
The plate boundary décollement zone in the Muroto
region of the Nankai accretionary prism records deformation
and consolidation histories that have been
affected by temporal changes in fluid pressure
(Fig.). Microstructural observations and chemical
analysis demonstrate that the décollement zone initiated
in an interval of porous clayey sediments characterized
by cementation due to intergranular bonding of
Shearing Along Sets
of Slip Surfaces
preferred orientation
of clay particles
Temporal Progression of Deformation
Destruction of Cementation
and Consolidation
Cementation due to
Intergranular Bonding
10µm
2 cm
random particle
orientation
random particle
orientation
10µm
clay aggregates
Fig.21 Schematic diagram showing the temporal progression of deformations in the decollement zone.
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