The%20Sumatra%20Subduction%20Zone:%20A%20Case%20for%20a%20Locked%20Fault%20Zone%20Extending%20into%20the%20Mantle

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The Sumatra Subduction Zone A Case for a Locked
Fault Zone Extending into the Mantle

• M. Simoes, J. P. Avouac, R Cattin and P. Henry
• JGR 109, 2004

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Dec. 26, 2004 Sumatra Eq.

• M 9.0
• Rupture 450 km by 40 km with up to 20 m of slip
• Deadliest earthquake (gt 200,000 deaths).
• Previously two bigger ones in the south 1833 M9
  and 1861 M8.5

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Subduction EQ process
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Scientific Questions Addressed

• What is the downdip extent of the locked fault
  zone (LFZ) of the Sumatra subduction?
• What parameters/processes control the transition
  from the LFZ to aseismic stable sliding zone?
• Current thought Thermally activated 325-350?C
  for crustal rocks and 750C for mantle rocks.
• For thin crust, the transition occurs at Moho
  because presence of serpentinite or other
  hydrated minerals in the mantle wedge would allow
  aseismic slip.

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Importance of the Work

• Assessing seismic hazard along subduction zones
• Understanding physical factors governing LFZ
  downdip extent.

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The bottom line

• The transition from the LFZ to the stable sliding
  zone of the Sumatra subduction occurs in the
  mantle.

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Sumatra Subduction Zone
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Downdip end of LFZ
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Down-dip end of LFZ
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Conclusions

• LFZ of the Sumatra subduction extends to a
  horizontal distance of 132 km from the trench and
  to a depth of 46 km.
• Gravity, seismic refraction, and seismicity data
  show that the slab interface intersects the
  forearc Moho at a depth of 30 km
• The transition from the LFZ to the stable sliding
  zone occurs in the mantle.
• Either the mantle is not serpentinized, or its
  presence does not simply stable sliding