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Idealised Transform Boundary 1 (1. Geological Features (Clay-rich gouge 0…
Idealised Transform Boundary 1
1. Geological Features
Clay-rich gouge
0 - 6 km
Diagenetic zone
Cataclasite (+pseudotachylite) 6-12 km
Sub-greenschist metamorphism
Mylonite
12-18 km
Lower greenschist
18 km + Upper Greenschist
2. Seismic behaviour
Stable
0-6 km
but ruptures may propagate through from below
Seismogenic zone
6-12 km
Earthquake nucleation
Transition zone btwn seismic & aseismic ~12 and bit over
Aseismic creep
approx > 12 km
3. Deformation mechanisms
0-6 km
Soft sediment granular flow
Dissolution precipitation creep
Frictional faulting
6-12 km
Dissolution precipitation creep
Frictional faulting
12-18 km
Dislocation creep
Dissolution precipitation creep
~13 km Seismic/Aseismic transition
4. Deformation/ Strength
Discontinuous Deformation
0-12 km
Pressure dependent frictional faulting
Linear part - Byerlee's law determines rock strength
Curved depression at depth = diss-precip creep
Continuous Deformation
12-18 km
Temperature dependent viscous flow mechanisms
Soft sediment granular flow
Unconsolidated sediment (porous) lacks frictional strenngth
Granular flow involves:
Grain rolling
Frictional grain boundary sliding
Due to:
Shearing
Compaction
At shallow depths (< 6km)
Cataclastic
flow
(6-12 km)
Non porous / low porosity
Fractures increasingly abundant
Fractures develop @ initial deformation stage
Cataclastic flow involves
Frictional sliding along fractures
Grain rotation
Main deformation mechanism above the brittle-ductile transition zone
Dissolution Precipitation Creep
(0-18 km)
1. Stress-dependent dissolution
of minerals
i.e. in fluids where stress = high
2. Transport by diffusion through grain boundary fluid
3. Reprecipitation where stress = lower
involves mass transfer in fluid
Grain size sensitive creep
Temperature activated creep mechanisms
Grains move ∴ involves granular flow component
Rocks never lose cohesion
∴ Differs from process near surface
Viscous grain boundary sliding