Deep Seismicity The Problem

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Deep Seismicity The Problem
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Sumatra
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Japan Trench
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Tonga-Fiji
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Idealised Fault
sn
At failure tmsn
s1 s3
t
b
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Mohr failure envelope
m
Shear Stress,t
Failure criterion
2b
Tension
Compression
Normal Stress,s
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Strength of rocks
Shear Strength, t
Temperature
Brittle envelope
Ductile envelope (constant strain-rate)
Depth
Depth
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Depth
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Deep Seismicity The Problem
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Models-Dehydration embrittlement
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Models-Remobilisation
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Models-anitcracks
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Models-Plastic instability (Shear Locallisation)
Complex feedback mechanism Heating weakens
fault Reduced strength Reduces heating

• Shear heating
• Melting
• Grain size reduction
• Transformation
• Fluid flux locallisation