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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:. 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

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  1. The Role of Advection on Fault Zone Temperature after an Earthquake Patrick Fulton Oregon State University

  2. 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?

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

  4. Model Domain Atmospheric Temperature and Pressure No flow boundary Basal heat flux 2D coupled fluid flow and heat transport

  5. Model Parameters

  6. Starting Conditions • Fault: • heat from earthquake • lithostatic fluid pressure • Crust: • background geothermal gradient • overpressured (80% lithostatic)

  7. Frictional Heat Generation

  8. 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

  9. Extract Borehole Temperature from 2D Model Results Results do not include effects of drilling

  10. Same permeability everywhere 1 year 2 years 3 years 6 years

  11. Fault conduit in low perm. crust Not to scale 1 year 2 years 3 years 6 years

  12. Fault barrier in permeable crust Not to scale 1 year 2 years 3 years 6 years

  13. 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

  14. With lower heat generation?

  15. With low heat generation

  16. With low heat generation Permeability same everywhere Fault conduit Fault barrier

  17. How can we tell if disturbed?

  18. Comparing repeat logs with diffusive prediction

  19. 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.

  20. Questions?

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