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S. Schmitt, C. DeMets, J. Stock, O. Sanchez, T. Masterlark, B. Marquez-Azua

Toward an Improved Understanding of Subduction Zone Mechanics Finite Element Modeling Results From the Jalisco GPS Project, 1993-2004. S. Schmitt, C. DeMets, J. Stock, O. Sanchez, T. Masterlark, B. Marquez-Azua Past contributions from W. Hutton, T. Melbourne, I.S.E. Carmichael, K. Hudnut.

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S. Schmitt, C. DeMets, J. Stock, O. Sanchez, T. Masterlark, B. Marquez-Azua

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  1. Toward an Improved Understandingof Subduction Zone MechanicsFinite Element Modeling Results Fromthe Jalisco GPS Project, 1993-2004 S. Schmitt, C. DeMets, J. Stock, O. Sanchez, T. Masterlark, B. Marquez-Azua Past contributions from W. Hutton, T. Melbourne, I.S.E. Carmichael, K. Hudnut

  2. Postseismic subduction zone processes • Relocking of rupture area • Downdip propagation of slip—“afterslip” • Viscoelastic relaxation

  3. Jalisco GPS network setting

  4. Modeling • Finite element modeling with ABAQUS code • Allows for realistic geometry and material properties • Can model static and transient deformation

  5. 9 October 1995—MW = 8.0 6.5 - 7.5 m maximum slip 22 January 2003—MW = 7.4 ~2.5 m maximum slip Major earthquakes Geodetic and seismic solutions agree

  6. COLI time series

  7. Interseismic motion • Elastic model • Completely locked interface at full plate convergence rate

  8. Interseismic Coseismic Coseismic displacement Release of elastic strain

  9. Near term postseismic What are the transient processes? • Afterslip and/or viscoelastic flow Viscoelastic model fails to predict direction and vertical motion • Log-linear model fits better • than log-only model • Relocking

  10. Very near-term postseismic Coseismic subsidence… …subsequent uplift Migration of slip down-dip

  11. Long-term postseismic Assume interseismic velocity from pre-1995 Extrapolate decaying afterslip rate from near-term postseismic Need another process for westward bias—viscoelasticity

  12. Long-term postseismic Viscoelastic prediction agrees well with subsequent observation

  13. Summary • Afterslip is needed to fit postseismic vertical motion, site direction, and decaying motion. • Viscoelastic flow is necessary to predict the directions in the velocity field. • Linear component implies relocking of the seismogenic zone soon after the earthquake.

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