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Deformation processes in great subduction zone earthquake cycles

This dissertation consists of two parts and investigates the crustal deformation associated with great subduction zone earthquake at two different spatial scales. At the small scale, I investigate the stress transfer along the megathrust during great earthquakes and its effects on the forearc wedge. At the large scale, I investigate the viscoelastic crustal deformation of the forearc and the back arc associated with great earthquakes.
Part I: In a subduction zone, the frontal region of the forearc can be morphologically divided into the outer wedge and the inner wedge. The outer wedge which features much active plastic deformation has a surface slope angle generally larger than that of the inner wedge which hosts stable geological formations. The megathrust can be represented by a three-segment model, the updip zone (velocity-strengthening), seismogenic zone (velocity-weakening), and downdip zone (velocity-strengthening). Our dynamic Coulomb wedge theory postulates that the outer wedge overlies the updip zone, and the inner wedge overlies the seismogenic zone. During an earthquake, strengthening of the updip zone may result in compressive failure in the outer wedge. The inner wedge undergoes elastic deformation. I have examined the geometry and mechanical processes of outer wedges of twenty-three subduction zones. The surface slope of these wedges is generally too high to be explained by the classical critical taper theory but can be explained by the dynamic Coulomb wedge theory.
Part II: A giant earthquake produces coseismic seaward motion of the upper plate and induces shear stresses in the upper mantle. After the earthquake, the fault is re-locked, causing the upper plate to move slowly landward. However, parts of the fault will undergo continuous aseismic afterslip for a short duration, causing areas surrounding the rupture zone to move seaward. At the same time, the viscoelastic relaxation of the earthquake-induced stresses in the upper mantle causes prolonged seaward motion of areas farther landward including the forearc and the back arc. The postseismic and interseismic crustal deformation depends on the interplay of these three primary processes. I have used three-dimensional viscoelastic finite element models to study the contemporary crustal deformation of three margins, Sumatra, Chile, and Cascadia, that are presently at different stages of their great earthquake cycles. Model results indicate that the earthquake cycle deformation of different margins is governed by a common physical process. The afterslip of the fault must be at work immediately after the earthquake. The model of the 2004 Sumatra earthquake constrains the characteristic time of the afterslip to be 1.25 yr. With the incorporation of the transient rheology, the model well explains the near-field and far-field postseismic deformation within a few years after the 2004 Sumatra event. The steady-state viscosity of the continental upper mantle is determined to be 10^19 Pa S, two orders of magnitude smaller than that of the global value obtained through global postglacial rebound models. / Graduate

  1. http://hdl.handle.net/1828/3267
  2. Hu, Y. (2011), Deformation processes in great subduction zone earthquake cycles, Ph.D. dissertation, University of Victoria, Victoria, British Columbia, Canada.
  3. Hu, Y., and K. Wang (2006), Bending-like behavior of wedge-shaped thin elastic fault blocks, Journal of Geophysical Research, 111, B06409, doi:10.1029/2005JB003987.
  4. Hu, Y., and K. Wang (2008), Coseismic strengthening of the shallow portion of the subduction fault and the effects on the frontal prism taper, Journal of Geophysical Research, 113(B12), B12411, doi:10.1029/2008JB005724.
  5. Hu, Y., K. Wang, J. He, J. Klotz, G. Khazaradze (2004), Three-dimensional viscoelastic finite element model for post-seismic deformation of the great 1960 Chile earthquake, Journal of Geophysical Research, 109, B12403, doi:10.1029/2004JB003163.
  6. Wang, K., J. He, and Y. Hu (2006), A note on pore fluid pressure ratios in the Coulomb wedge theory, Geophysical Research Letters, 33, L19310, doi:10.1029/2006GL027233.
  7. Wang, K., and Y. Hu (2006), Accretionary prisms in subduction earthquake cycles: The theory of dynamic Coulomb wedge, Journal of Geophysical Research, 111, B06410, doi:10.1029/2005JB004094.
  8. Wang, K., Y. Hu, M. Bevis, E. Kendrick, R. Smalley Jr., R. B. Vargas, and E. Lauría (2007), Crustal motion in the zone of the 1960 Chile earthquake: Detangling earthquake-cycle deformation and forearc-sliver translation, Geochemistry, Geophysics, and Geosystems, 8(10), Q10010, doi:10.1029/2007GC001721.
  9. Wang, K., Y. Hu, and J. He (2009), Wedge mechanics: Relation with subduction zone earthquakes and tsunamis, in Encyclopedia complexity and system science, Volume x, edited by R. Meyers, Springer, New York.
  10. Wang, K., Y. Hu, R. von Huene, and N. Kukowski (2010), Interplate earthquakes as a driver of shallow subduction erosion, Geology, 38(5), 431-434, doi: 10.1130/G30597.1.
Identiferoai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVIV.1828/3267
Date29 April 2011
CreatorsHu, Yan
ContributorsWang, Kelin, Spence, George D.
Source SetsLibrary and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada
LanguageEnglish, English
Detected LanguageEnglish
TypeThesis
RightsAvailable to the World Wide Web

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