Intraplate Deformation Southeast of Kii Penninsula

1
Intraplate Deformation Southeast of Kii Penninsula

• Presented by
• P. Henry CNRS/Collège de France,
  Aix-en-Provence
• after discussions with X. Le Pichon
• and previous work by
• P. Huchon, S. Lallemant, S. Mazzotti and others
• September 5 earthquakes and aftershocks are
  intraplate earthquakes within the Shikoku oceanic
  basin and are related to the Izu-Zenisu zone of
  deformation.

2
Map ofE Nankai

• Zenisu and
• Paléo-zenisu
• Combination of Miocene arc volcanism and active
  tectonics

To-Nankai 1944
Nantroseize
Next big one ?
3
Subduction earthquakes ?

• Unlikely !
• slip vectors uncompatible with subduction motion
• only one determination has low dip plane
• location is too close to trench axis

USGS
NIED
Harvard
4
Izu-Zenizu active faults and seismic activity
5
Zenisu-Izu deformation zone kinematics

• Mazzotti et al. (1999)
• Philippine Sea Plate / Central Japan in blue
• Philippine Sea Playe / Zenisu West Izu block in
  red (Intraplate)
• Zenisu West Izu / Central Japan in green
  (Subduction)
• 2004 NIED focal mechanisms added

6
Kinematic model taking into account deformation
onland Japan (Mazzotti et al., 2001)
7
Rigid body kinematic solutionsfor Izu-Zenisu
deformation zone

• predicted convergence at location of main shock
  (04/09/05 - 1457 U.T. - Mw 7.5)
• 1/4 to 1/3 of plate convergence takes place on
  Zenisu ridge

8
First 24 hours focal mechanisms (NIED - 5-6
september 2004)
9
9 days focal mechanisms (NIED - 5-15 september
2004)
Zenisu
W Zenisu
10
Old profiles across West Zenisu show
intra-oceanic thrusts(Aoki et al., 1982)
(Lallemant et al., 1989)
(Le Pichon et al., 1987)
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Evidence for active thrusting on line KR9806-2
3 km
NT1-04A?
4 km
5 km
6 km
7 km
8 km
9 km
12
Profile along Trench
Zenisu
West Zenisu
13
KR9806-1
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Hypocenters (Hi-net data)
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Interpretation
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Conclusion and questions

• The Zenisu system may cause large earthquakes and
  tsunamis
• Can seismogenic faults in the oceanic crust be
  considered as drilling targets (e.g. as part of
  phase 1) ?
• What is the Coulomb stress change on Zenisu
  thrusts and on the subduction megathrust in the
  Kii and Tokai segments ?