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The Role of Advection on Fault Zone Temperature after an Earthquake. Patrick Fulton Oregon State University. Questions:. If we see temperature anomaly: Heterogeneity, frictional heat, or fluid upflow along fault?

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the role of advection on fault zone temperature after an earthquake

The Role of Advection on Fault Zone Temperature after an Earthquake

Patrick Fulton

Oregon State University

questions
Questions:
  • If we see temperature anomaly:
    • Heterogeneity, frictional heat, or fluid upflow along fault?
    • Heterogeneity may generate 0.1 oC differences along geotherm (Tanaka et al. 2007)
  • If temperature anomaly is small or not observable:
    • Does this mean low shear stress during slip?
    • Could groundwater flow have washed away the heat?
slide3

What effect does transient groundwater flow after an earthquake have on fault zone temperature?

model domain
Model Domain

Atmospheric Temperature and Pressure

No flow boundary

Basal heat flux

2D coupled fluid flow and heat transport

starting conditions
Starting Conditions
  • Fault:
  • heat from earthquake
  • lithostatic fluid pressure
  • Crust:
  • background geothermal gradient
  • overpressured (80% lithostatic)
hydrologic scenarios
Hydrologic Scenarios

Same everywhere

Fault conduit

Fault barrier

Permeable

fault zone

(10 m thick)

Low-permeability crust

Low-permeability fault zone

(10 m thick)

Permeable crust

Permeable everywhere

Low permeability zones: 10-18 m2

Permeable zones: 10-17 m2 – 10-14 m2

extract borehole temperature from 2d model results
Extract Borehole Temperature from 2D Model Results

Results do not include effects of drilling

same permeability everywhere
Same permeability everywhere

1 year

2 years

3 years

6 years

fault conduit in low perm crust
Fault conduit in low perm. crust

Not to scale

1 year

2 years

3 years

6 years

fault barrier in permeable crust
Fault barrier in permeable crust

Not to scale

1 year

2 years

3 years

6 years

summary
Summary
  • Only models with k >= 10-14 m2 have a significant effect on temperature within 6 yrs after an earthquake.
  • When crustal permeability is high, temperature may be reduced
  • When fault zone permeability is high, temperature may be increased slightly
with low heat generation1
With low heat generation

Permeability

same everywhere

Fault conduit

Fault barrier

summary1
Summary
  • High permeability (>10-14 m2) needed before significant temperature disturbance
    • Transiently high permeability after an earthquake?
    • Country rock permeability important for reducing anomaly
  • Even withlow frictional heat and groundwater flow, anomaly > 0.1 oC observable within 2 yrs
  • Repeat logs may help describe advective component and effects of heterogeneity.
    • Earlier the better for initial log.