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interseismic deformation with aseismic stress-dependent fault slip

a very informal, and preliminary talk about how we are thinking about. interseismic deformation with aseismic stress-dependent fault slip. Eric A Hetland, Mark Simons, Ravi Kanda, Sue Owen. TO brown-bag – 03 April 2007. post-seismic slip following subduction ruptures:. Hsu et al., 2006.

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interseismic deformation with aseismic stress-dependent fault slip

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  1. a very informal, and preliminary talk about how we are thinking about interseismic deformation with aseismic stress-dependent fault slip Eric A Hetland, Mark Simons, Ravi Kanda, Sue Owen TO brown-bag – 03 April 2007

  2. post-seismic slip following subduction ruptures: Hsu et al., 2006 2005 Nias-Simeulue eq. (M8.7) fault rheology is not (explicitly) included in after-slip model

  3. post-seismic slip following subduction ruptures: Pritchard & Simons, 2006 1995 Antofagasta eq. (M8.1) fault rheology is not (explicitly) included in after-slip model

  4. post-seismic slip following subduction ruptures: Baba et al., 2003 2003 Tokachi-oki eq. (M8) fault rheology is not included in after-slip model

  5. inter-seismic slip near regions of past subduction ruptures: Japan/southern Kurile trenches Suwa et al., 2006 model assumes fault slip during inter-seismic period is constant

  6. Suwa et al., 2006 Baba et al., 2003 we want an internally consistent model that can describe observations of both inter-seismic and post-seismic deformation… for now we are building subduction zone models that include repeated ruptures, on assumed asperities, with stress-dependent aseismic slip on the non-asperity portions of the subduction interface during the interseismic period…

  7. includes the off-fault rheology slip on the fault (Burgers vector) traction on the fault finite fault plane in 1/2-space long-term fault-slip with fault loading: elastic half-space U’ cuts 1/2-space L

  8. with fault loading: =0 e.g.; Rice, 1993; Liu and Rice, 2005. Note: no seismic radiation damping (e.g., Rice, 1993) - there are no seismic waves & no problems with unbounded slip velocities in our models…

  9. red = lots of BS white = no BS “back-slip” Suwa et al., 2006 + = Savage & Burford, 1973; Savage & Prescott, 1978 introduced by J. Savage (Savage and Burford, 1973; Savage and Prescott, 1978; Savage, 1983) as a mathematically convenient fault loading mechanism in kinematic & quasi-kinematic models approximation only good for spun-up systems: rate of interseismic relaxation = rate of reloading

  10. imposed ruptures at times Tp long-term fault-slip interseismic slip on fault traction on fault part of fault with coseismic slip part of fault that slips steadily part of fault that is allowed to slip interseismically locked - ’ -   we impose ruptures - we do not solve for them:

  11. RS-friction (e.g. Marone et al., 1991) non-linear viscous (Montesi, 2004) linear viscous we impose ruptures - we do not solve for them: imposed ruptures at times Tp long-term fault-slip interseismic slip on fault traction on fault part of fault with coseismic slip part of fault that slips steadily part of fault that is allowed to slip interseismically need a fault rheology:

  12. rate- and state-friction (a-b)<0  “ruptures”, (a-b)>0  “aseismic slip”  is a state variable, assume it is constant  = L/v  = N Dieterich, 1979; Ruina 1983; Rice and Gu, 1983 (figure from Ben-Zion, 2003)

  13. Ben-Zion, 2003 Lapusta et al., 2000

  14. given by we impose ruptures - we only solve for aseismic slip: fault rheology: bulk rheology: for now, assume elastic half-space and use Okada, 1992 use boundary elements… model works for 3D, non-planar faults, with multiple asperities, arbitrary rheologic parameters, we allow both dip- and strike-slip co- and inter-seismic slip, and irregular (imposed) rupture sequences currently, we can impose coseismic slip in non-locked regions of the fault, but we do not allow interseismic slip in the locked regions…

  15.  = 30 GPa ’N = 300 MPa D = 104 m bo = 10 m  (a-b) = -1/10 -1 = 0.5  (a-b) = 0.05 -1 = 1.0  (a-b) = 0.10

  16. D/2 locked section 10D D steady slip at depth modification of ubiquitous subduction back-slip model, by allowing interseismic slip here “thrust fault” in an elastic half-space, dipping 45 degrees

  17. D/2 locked section 10D D steady slip at depth “thrust fault” in an elastic half-space, dipping 45 degrees a more realistic geometry back-slip model interseismic surface deformation is given by the locked portions of the mega-thrust sliding as a normal fault at the plate rate (Savage, 1983) vertical horizontal

  18. D/2 locked section 10D D steady slip at depth “thrust fault” in an elastic half-space, dipping 45 degrees a more realistic geometry elastic slab model does not include strains due to plate bending, if incorporated, discrepancy removed, total interseismic + coseismic = subduction block motion… vertical horizontal Ravi Kanda

  19. D/2 locked section 10D D steady slip at depth in a spun-up model, total interseismic slip fills in the the areas above the co-seismic slip-profile “thrust fault” in an elastic half-space, dipping 45 degrees periodically impose this co-seismic slip

  20. slip on the fault: below the locked region b>0  thrust slip

  21. o o xxxxxx surface interseismic displacements:

  22. o o o xxxxxx surface interseismic displacements:

  23. 2003 Tokachi-oki eq. (M8) x slight curvature tectonic? Baba et al., 2003 data from Sue Owen surface interseismic displacements motivation:

  24. surface interseismic displacements motivation: 2003 Tokachi-oki eq. (M8) Baba et al., 2003 data from Sue Owen x

  25. determination of plate coupling: Suwa et al., 2006 shown is back-slip rate vbs this assumes that the interseismic deformation is constant throughout the interseismic period • invert GPS velocities for distributions of normal slip (vbs) on the mega-thrust • use back-slip model (Savage, 1983) to determine the “coupling coefficient” • vbs = vT coupled (C=1) • vbs = 0  uncoupled (C=0)

  26. determination of plate coupling: D/2 locked section 10D D steady slip at depth this assumes that the interseismic deformation is constant throughout the interseismic period • invert GPS velocities for distributions of normal slip (vbs) on the mega-thrust • use back-slip model (Savage, 1983) to determine the “coupling coefficient” • vbs = vT coupled (C=1) • vbs = 0  uncoupled (C=0) slip is not constant through the cycle

  27. xxx variation of coupling through an interseismic period xxxxxx

  28. xxxxxx variation of coupling through an interseismic period

  29. xxxxxx variation of coupling through an interseismic period

  30. Lapusta et al., 2000 this model only contains co-seismic slip in the locked regions, no interseismic slip-allowed in the locked regions… contrary to dynamic calculations…

  31. two (of the many) remaining issues: still learning to drive… “lockedness” – we assume full slip in locked patches (asperities) some directions currently aiming for: include heterogeneous elastic structure by computing K(z;) from FE models… include other bulk rheologies – K(z;): “simple” semi-analytic models & quite complicated FE models… model the GPS data of inter- & post-seismic observations in Hokkaido (2D, 3D planar, respecting slab geometry, & …)

  32. gOcad 1973 2003 1968 slip models from Yamanaka and Kikuchi (2002) vertically exaggerated

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