Transcript Crustral structure across the Southern Japanese Alps segment of

Seismicity along the ItoigawaShizuoka Tectonic Line (ISTL)
南アルプス地域・糸魚川-静岡構造線断
層帯付近の地震活動
ヤニス パナヨトプロス[1]; 平田直[1]; 今西和俊[2]; 長郁夫[2]; 桑原保人
[2]; 加藤愛太郎[1]
Yannis Panayotopoulos[1]; Naoshi Hirata[1]; Kazutoshi Imanishi[2];
Ikuo Cho[2]; Yasuto Kuwahara[2]; Aitaro Kato[1]
[1] 東大・地震研; [2] 産総研;
[1] ERI, Univ. Tokyo; [2] GSJ, AIST;
Speaker: Yannis Panayotopoulos 発表者：ヤニス パナヨトプロス
North : Northern Fossa
Magna sedimentary
units and old
Japanese accretionary
prism rocks boundary.
South : Izu-Bonin units and
present Japanese
accretionary prism
rocks boundary.
I.S.T.L
Mt. Fuji 
A 5 year project aiming to investigate the seismicity
and tectonic setting along ISTL.
Derive a 3d velocity model for the entire ISTL
region and correlate it with the geologic structures
in the area.
Correlate the regional seismicity with movement of
the different segments of the ISTL fault system.
2005 research: The south central part of ISTL in
the Southern Japanese
Alps and Kofu
basin area.
Stations
• 2 seismic arrays with 26
or 30 stations each with
1-1.5 km spacing.
• 6 stations (+ 8 AIST)
distributed in the area.
• 100 telemetric stations
(JMA, NAID, UNI)
• 3 component 1 Hz
seismometers and
removable HD recorders.
• Recording period from
2005/09/16 to 2005/12/22
• Selected 610 JMA catalog
hypocenters (M >0.5)
from 2005/09/01 to
2005/12/31 (JMA total
1721)
• Manually picked 83,053 P
and S phase arrivals
(31,147 JMA)
• Selected 348 events near
Minami alps and 11 shots
(100~300 kg) for
tomography inversion
ERI average
Vp (km/sec)
4
5
6
7
8
9
0
5
Depth (km)
10
15
20
25
30
35
40
ERI average
Method：
Double-difference
tomography
(Zhang and Thurber 2003)
Grid points：
x: 5km spacing for the
central 60km、１５ｋｍ
or ２０ｋｍ in the
perimeter.
y: 9 lines at -54, -32, 16, -8, 0, 8, 16, 32, 54
km.
At depth:
0、3, 6, 9, 12,16, 20,
30, 35, 100, 200 km
y
x
Double Difference
relocated events
JMA - DD depth (km)
10
8
6
4
2
0
-2
-4
0
10
20
30
40
JMA depth (km)
50
Relocated hypocenters
appear to be 1.5 km
shallower than the JMA
estimation.
Results
Vp cross sections for the grid
lines located at 8, 0, -8 km.
Blue ●: relocated hypocenters
Red ●: JMA hypocenters
Major
geological units
in the area.
Yatsugatake Volcano
Chichibu Belt
Ryoke belt: Granitic
rocks.
Simanto belt: flysch,
shale and chert.
ISTL
Ryoke Belt
Active Fault
ISTL
MTL
Shimanto Belt
Mt. Fuji
Izu-Bonin
Chichibu belt: pillow
basalt, reef limestone
radiolarian
chert.
Yatsugatake volcano:
Volcanic tuffs.
Izu-Bonin: Volcanic
rocks
Discussion
ISTL
MTL
MTL
MTL
ISTL A.ISTL
ISTL
A.ISTL
Active Fault
ISTL
Seismicity may be related
to ISTL movement at the
northern cross section (8
km).
ISTL dipping to the west at
450 ~ 550.
MTL
ISTL A.ISTL
Conclusions
The deeper extension of ISTL in southern Alps
region seems to be the boundary between low Vp
and high Vp zones, which can be identified as the
accretionary prism units and the Izu-Bonin arc
sequences.
ISTL forms a thrust fault that dips approximately
450~550 towards the west.
The seismicity below the northern profile may occur
on the deeper extension of the ISTL. If so, this
could be evidence that the deeper part of the
geological ISTL is connected to the active fault at
depth.
Checkerboard resolution test for
the grid lines located at 8, 0, -8 km.
SW
NE
SW
NE
SW
NE