Transcript Yannis PANAYOTOPOULOS

SEISMICITY AND CRUSTALL STRUCTURE
ALONG THE SOUTHERN JAPANESE ALPS
SEGMENT OF THE ITOIGAWA-SHIZUOKA
TECTONIC LINE (ISTL)
Yannis PANAYOTOPOULOS [1], Naoshi HIRATA [1], Hiroshi SATO [1], Aitaro
KATO [1], Kazutoshi IMANISHI [2], Ikuo CHO [2], Yasuto KUWAHARA [2]
[1] ERI, Univ. Tokyo; [2] GSJ, AIST;
Speaker: Yannis Panayotopoulos
・Geology
The geological setting along the ItoigawaShizuoka tectonic line (ISTL).
• Northern J-Alps ISTL: western boundary
of the Northern Fossa Magna rift basin 、
east dipping faults.
• Southern J-Alps ISTL： boundary
between the Izu-Bonin Arc crust and the
Honshu Island crust (Chichibu-Shimanto
belts).
I.S.T.L
Mt. Fuji 
・Objectives
• Investigate the relation between the micro
earthquake activity ,crustall velocity structure and
geological structure in the vicinity of the ISTL and
correlate it with its present time activity.
• For this purpose:
• We monitor the seismicity in the southern part
of the ISTL.
• Estimate the 3D seismic wave velocity
structure and compare it with the geological
structure in the area.
• Investigate the relation between the regional
seismicity and the active parts of the ISTL
fault system.
・Stations
1. From 2003/8/25 to
2003/10/16
• 1 linear station array
of 58 offline
recorders
2. From 2005/9/16 to
2005/12/22
• 2 lines of 26 and 30
offline stations
• 14 more stations in
collaboration with
the Japanese
Geological Survey
Institute
3. Near by 100 online
Japanese national
network stations
・Selected events
From 2003/08/25~10/16 and 2005/09/01~12/31 • 89 events from 2003/08/25
to 2003/10/16, recorder by
the 2003 probe
• 348 M > 0.5 events from
2005/09/01 to 2005/12/31,
recorded by the 2005 probe
• 13 explosion scheduled for
the same period
• Manually repicked 83,053 P
and S faze arrivals
ERI average
Vp (km/sec)
4
5
6
7
8
9
0
5
Depth (km)
10
15
20
25
30
35
40
ERI average
・Data processing
Method：Double-difference
tomography
(Zhang and Thurber 2003)
Grid point distribution：
x-axis：5km spacing for the
central 60km、１５ｋｍ or ２
０ｋｍ spacing for the rest
y-axis：8km spacing for the
central 5 lines, 16 and 24
for the outer lines
at depth：0、3, 6, 9, 12,16,
20, 30, 35, 100, 200 km
y
x
2005/09/01~12/31
DD relocated
events
10
JMA - DD depth (km)
・Results（１）
8
6
4
2
0
-2
-4
0
10
20
30
40
JMA depth (km)
50
The difference between
the hypocenter depth
published by the
Japanese National
Meteorological agency
and the one relocated by
this study progressively
grows with depth.
・Results（２）

Wakamiya
MTL
East-west Vp
cross sections
near each
fault segment

Aoyagi
Mechanism solutions
Imanishi et al、2006
Hakushu
Shimotsuburai
Hoouzan


Ichinose
Mechanism solutions
Imanishi et al、2006
Onajika-toge



 
Mechanism solutions
Imanishi et al、2006


・Discussion（１）
Hakushu
MTL
Cross section near
Hakushu fault
MTL
Hakushu(ISTL)
発震機構解
今西・他、2006
・Discussion（２）
Chichibu-Shimanto
belts
Onajika-toge
Koma block
(Tanzawa)
Onajika-toge
Ichinose
Cross section and
geology near
Ichinose and
Onajika-toge faults
Kofu Basin
Ichinose（ISTL)
Yamanashi Pref. (2004)
Kofu Basin
Misaka block (pIc)
(Tanzawa)
・Conclusions
•
The deeper extension of the ISTL in the southern
Japanese Alps region becomes the boundary
between a low and a high Vp region. We identify
the low Vp region as the Chichibu-Shimanto
accretionary prism belts of the Honshu island crust
and the high Vp region as part of the Izu-Bonin
arc paleo-crust.
•
The ISTL deeper extension, forms an
approximately 500 west dipping thrust fault.
•
The seismic activity near the Hakushu fault
segment occurs on the ISTL.
•
The crustall structure near the Ichinose fault also
has the characteristics of a west dipping thrust.