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( Calo et al, GJI, 2011)

( Calo et al, GJI, 2011). Reservoir-Induced Seismicity. Victoria Stevens February 2012. References. Talwani , P., 1997. On the nature of reservoir-induced seismicity, Pure and Applied Geophysics, 150 , 473-492.

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( Calo et al, GJI, 2011)

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  1. (Calo et al, GJI, 2011)

  2. Reservoir-Induced Seismicity Victoria Stevens February 2012

  3. References • Talwani, P., 1997. On the nature of reservoir-induced seismicity, Pure and Applied Geophysics, 150, 473-492. • Talwani, P., Chen, L. & Gahalaut, K., 2007. Seismogenic permeability, k(S), Journal of Geophysical Research-Solid Earth, 112. • Gupta, H., 2002. A review of recent studies of triggered earthquakes by artificial water reservoirs with special emphasis on earthquakes in Koyna, Earth Science Reviews, 58, 279-310.

  4. Plan of talk • Introduction • Observations • Mechanisms • Diffusivity and permeability

  5. Introduction • Noticed first when Lake Mead (on Arizona-Nevada border) was filled • We know how and when conditions change so can study response • Triggered by as little as 20 m filling – crust already close to failure • M 6.3 triggered by reservoir filling in Koyna, India – killed 200 people.

  6. Worldwide distribution of reservoir induced seismicity, all over M 4

  7. Seismicity at Monticello Reservoir

  8. Lake Mead

  9. Koyna Seismicity from 1962 - present

  10. USGS NEIC PDE 2000 to 2012 India Earthquake Catalog 1960 to 1970

  11. Three time scales of seismicity • Initial • Loading from water • increased pore pressure • Delayed • Diffusion of pore pressure • Protracted • Subsequent changes in water level

  12. 1. Initial seismicity • Effect of load

  13. Initial seismicity • Poroelasticconstitutive equations: • = volume strain increment • B = Skempton’s coefficient • = undrained Poisson’s ratio • G = shear modulus • = change in normal stress

  14. 2. Delayed seismicity • Diffusion of pore pressure • is permeability • is viscosity of pore fluid • is compressibility of bulk rock

  15. Coupled poroelastic response • Effect of load + diffusion of pore pressure • B Skempton’s coefficient • is the undrained Poisson’s ratio • H(t) is Heaviside unit step function • Assumptions……e.g. isotropic medium

  16. Changes in elastic stress and pore pressure

  17. 3. Protracted seismicity

  18. Diffusivity and permeability • Talwani et al. 2007 • Measured hydraulic diffusivity, C, from induced earthquakes • Found all fractures that produced seismicity had permeability of 5x10-16 to 5x10-14m-2 • Called this the seismogenic permeability • Assumed seismicity depends on rate of increase of pore pressure, dp/dt.

  19. Finding seismogenic values of C

  20. Narrow range of k causes earthquakes

  21. Hydraulic diffusivity

  22. Permeability • = viscosity of water, = porosity • and = compressibilities of water and rock

  23. THE END

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