Influence of temperature- and depth-dependent viscosity structures on postseismic deformation predictions for the large 1946 Nankai subduction zone earthquake

Katagi, Takeshi; Yoshioka, Shoichi; Hashimoto, Manabu

doi:10.1016/j.tecto.2008.01.006

Cited by 13 publications

(7 citation statements)

References 40 publications

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“…Laboratory experiments of rock deformation show that effective viscosities depend strongly on temperature, stress, mineralogy, and presence of water [e.g., Kirby , ; Karato , ; Karato et al ., ; Karato and Wu , ; Kohlstedt et al ., ; Ranalli , ; Hirth and Kohlstedt , ; Dimanov and Dresen , ; Korenaga and Karato , ; Mehl and Hirth , ], all of which imply spatial variation of effective viscosity. The increase of temperature with depth is probably one of the most important factors influencing crustal viscosity, as has been recognized in several studies of postseismic deformation [e.g., Katagi et al ., ; Riva and Govers , ; Yamasaki and Houseman , , ]. Lateral variations of crustal viscosity are also plausible, especially in the context of a major seismogenic zone beneath which lithological contrast, grain size reduction, shear heating, or fabric development may have developed [e.g., Billen and Houseman , ; Montési , , ; Dayem et al ., ; Platt and Behr , ; Takeuchi and Fialko , , ; Traoré et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Weak ductile shear zone beneath a major strike‐slip fault: Inferences from earthquake cycle model constrained by geodetic observations of the western North Anatolian Fault Zone

2014

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GPS data before and after the 1999 İzmit/Düzce earthquakes on the North Anatolian Fault Zone (Turkey) reveal a preseismic strain localization within about 25 km of the fault and a rapid postseismic transient. Using 3-D finite element calculations of the earthquake cycle in an idealized model of the crust, comprising elastic above Maxwell viscoelastic layers, we show that spatially varying viscosity in the crust can explain these observations. Depth-dependent viscosity without lateral variations can reproduce some of the observations but cannot explain the proximity to the fault of maximum postseismic velocities. A localized weak zone beneath the faulted elastic lid satisfactorily explains the observations if the weak zone extends down to midcrustal depths, and the ratio of relaxation time to earthquake repeat time ranges from~0.005 tõ 0.01 (for weak-zone widths of~24 and 40 km, respectively) in the weakened domain and greater than~1.0 elsewhere, corresponding to viscosities of~10 18 ± 0.3 Pa s and greater than~10 20 Pa s. Models with sharp weak-zone boundaries fit the data better than those with a smooth viscosity increase away from the fault, implying that the weak zone may be bounded by a relatively abrupt change in material properties. Such a change might result from lithological contrast, grain size reduction, fabric development, or water content, in addition to any effects from shear heating. Our models also imply that viscosities inferred from postseismic studies primarily reflect the rheology of the weak zone and should not be used to infer the mechanical properties of normal crust.

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Section: Introductionmentioning

confidence: 99%

Weak ductile shear zone beneath a major strike‐slip fault: Inferences from earthquake cycle model constrained by geodetic observations of the western North Anatolian Fault Zone

2014

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“…For the Nankai subduction zone, realistic models of viscoelastic structure using empirically derived temperature‐dependent viscosities with spatial heterogeneities have been developed [ Katagi et al ., ]. Given that the geodetic postseismic deformation field of the 1946 Nankai earthquake ( M 8.0) could not be explained by viscoelastic relaxation using a realistic viscosity structure, other effects (e.g., interplate coupling on the plate interface, afterslip, and poroelastic rebound) appear to be required to explain the deformation [ Katagi et al ., ]. These results clearly show that the detailed viscosity structure should be considered when attempting to accurately evaluate the viscoelastic relaxation component.…”

Section: Introductionmentioning

confidence: 99%

Two‐dimensional viscosity structure of the northeastern Japan islands arc‐trench system

Muto

Shibazaki

Ito

et al. 2013

Geophysical Research Letters

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Two‐dimensional viscosity profiles were constructed for the northeastern Japan islands arc‐trench system covering the source area of the 2011 Tohoku‐Oki earthquake. From seismologically determined models of lithospheric structure, experimentally derived constitutive laws of various rocks, and densely measured geothermal gradient data, we have predicted the steady state effective viscosity across the subduction zone. The profile reveals strong lateral viscosity gradients both parallel and normal to the trench axis. The detailed viscosity structures presented here contribute to accurate evaluation of viscoelastic relaxation components when modeling geodetically measured postseismic deformation at high spatial and temporal resolution.

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“…The DDV structure used in this study differs from previous multilayer models (e.g. Pollitz et al 1998; Hetland & Hager 2003, 2006; Vergnolle et al 2003); we define the creep viscosity here to have an exponential dependence on depth [as also used by Katagi et al (2008), Riva & Govers (2009) and Takeuchi & Fialko (2012)]. This model represents approximately the effect of temperature increasing with depth, simplified to facilitate exploration of the relevant parameter space.…”

Section: Introductionmentioning

confidence: 99%

The signature of depth-dependent viscosity structure in post-seismic deformation

Yamasaki

Houseman

2012

Geophysical Journal International

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SUMMARY Geodetic observations of post‐seismic ground motion reflect the integrated effects of several relaxation mechanisms. To evaluate the viscous relaxation component accurately the crustal viscosity structure beneath a region must be estimated. In this study, using a 3‐D finite element model, we describe the viscoelastic relaxation that follows an instantaneous strike‐slip faulting event in a crustal layer whose viscosity decreases exponentially with depth. At any surface observation point the depth‐dependent viscosity (DDV) model displacement history closely fits the history predicted for a uniform viscosity (UNV) model. The difference can be minimized to obtain the UNV viscosity (ηu) that best fits the DDV model displacement at that location. The differences in displacement histories between DDV and best‐fit UNV models are minor but depend on distance from fault, the viscosity gradient and the fault configuration. In the near field, the DDV model prediction can be well approximated by the UNV model, regardless of the viscosity gradient and fault configuration. On the other hand, in the far field, small differences between DDV model and best‐fit UNV model become apparent: the displacements are controlled by greater viscosities in later phases, and the differences are greater for DDV models with greater viscosity gradient. The more important result we obtain is that: apparent viscosity ηu decreases with distance from the fault, and its rate of decrease is directly diagnostic of the vertical viscosity gradient. This result points to a practical method of analysing post‐seismic ground‐displacement data for the variation of viscosity in the ductile crust; the apparent crustal viscosity should be determined at a series of points at increasing distance from the fault. The variation of apparent viscosity with distance can then be used to directly infer the vertical gradient of viscosity in the crust.

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Influence of temperature- and depth-dependent viscosity structures on postseismic deformation predictions for the large 1946 Nankai subduction zone earthquake

Cited by 13 publications

References 40 publications

Weak ductile shear zone beneath a major strike‐slip fault: Inferences from earthquake cycle model constrained by geodetic observations of the western North Anatolian Fault Zone

Weak ductile shear zone beneath a major strike‐slip fault: Inferences from earthquake cycle model constrained by geodetic observations of the western North Anatolian Fault Zone

Two‐dimensional viscosity structure of the northeastern Japan islands arc‐trench system

The signature of depth-dependent viscosity structure in post-seismic deformation

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