Effects of Three-dimensional Inhomogeneous Viscoelastic Structures on Postseismic Surface Deformations Associated with the Great 1946 Nankaido Earthquake

Yoshioka, Shoichi; Suzuki, Haruko

doi:10.1007/s000240050231

Cited by 14 publications

(6 citation statements)

References 29 publications

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“…The inclusion of the slab reduces the rate of the geoid height change by 30 per cent and the displacement rate by 70–80 per cent. The decrease caused by including the slab qualitatively agrees with the result of Yoshioka & Suzuki (1999), who constructed 3‐D structural models, using the finite‐element method without incorporating gravitational effects. The case studies show that these effects are not negligible for interpreting GRACE and GPS data, especially for large events that occur at a subduction zone with a lower viscosity.…”

Section: Discussionsupporting

confidence: 84%

Spectral finite element approach to postseismic deformation in a viscoelastic self-gravitating spherical Earth

Tanaka¹,

Klemann²,

Fleming³

et al. 2009

Geophysical Journal International

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S U M M A R YTheoretical models of the viscoelastic relaxation of a spherical Earth are derived to model large-scale postseismic deformation resulting from great earthquakes (M > 7) over decadal timescales. Most existing models of postseismic deformation do not consider strong lateral heterogeneities in mantle viscosity, in particular in the subducting slab where such events occur. In addition, the self-gravitation effect is often treated only approximately. Both effects become important when observations from space geodetic techniques such as GPS and GRACE are interpreted. In this paper, we present a spectral finite-element approach that allows these two effects to be considered in a rigorous way. In this way, much larger lateral viscosity variations can be handled than by perturbation techniques. We derive interface conditions for an arbitrary shear fault in the form of double-couple forces that are equivalent to a prescribed dislocation and simulate a relaxation process for an incompressible Maxwell earth with a 3-D viscoelastic structure. Computational results are validated for a spherically symmetric model by an independent method based on the inverse Laplace integration, and good agreement is obtained. As an example, we apply this approach to the 2004 Sumatra-Andaman earthquake and simulate a large-scale postseismic gravity potential variation by a forward calculation. In the presence of a slab, the secular variation in geoid height change decreases by 30 per cent for wavelengths longer than 500 km, with respect to the case excluding the slab. The effect of the slab can exceed 0.3 mm yr −1 for short-term variations when the asthenosphere viscosity is 10 19 Pa s, which are larger than the observation errors of GRACE. For a displacement field, a decrease in deformation rates can amount to 70 per cent due to the inclusion of a slab, which is detectable with geodetic observations such as GPS. The effect of the slab is attenuated in the gravity field for such longer wavelengths since horizontal scales of the slab are smaller than its spatial resolution. Lateral heterogeneities in viscosity due to a slab should therefore be considered for interpreting observed postseismic relaxation due to a large thrust event in a subduction zone.

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Section: Discussionsupporting

confidence: 84%

Spectral finite element approach to postseismic deformation in a viscoelastic self-gravitating spherical Earth

Tanaka¹,

Klemann²,

Fleming³

et al. 2009

Geophysical Journal International

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“…This is because surface deformation due to local viscoelastic flow in the wedge mantle is limited owing to the shallow dip angle of the slab in the young subduction zone, and the deformation due to viscoelastic flow beneath the oceanic lithosphere is dominant. Hence, we could interpret the 50‐km‐thick lithosphere in Yoshioka and Suzuki () and the 60‐km‐thick lithosphere in our model as the bottom depth of the elastic slab beneath the seismogenic zone.…”

Section: Discussionmentioning

confidence: 80%

“…In this study, we ignored heterogeneity in the structure, such as a subducting slab and different thicknesses between the continental and oceanic lithosphere. Comparison of horizontal layered and heterogeneous models performed by Yoshioka and Suzuki () helps us consider the difference between two models in viscoelastic relaxation, although they did not investigate the completely relaxed responses directly. From their simulations of postseismic surface deformations due to viscoelastic relaxation caused by the 1946 Nankai earthquake, we can see that the horizontal displacements in a horizontally layered structure with a 50‐km‐thick lithosphere are similar to that in a heterogeneous structure with the subducting slab.…”

Section: Discussionmentioning

confidence: 99%

Slip‐Deficit Rate Distribution Along the Nankai Trough, Southwest Japan, With Elastic Lithosphere and Viscoelastic Asthenosphere

2018

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In southwest Japan, great earthquakes have occurred on the plate interface along the Nankai trough with a recurrence time of approximately 100 years. Most previous studies estimated slip deficits on the seismogenic zone from interseismic Global Navigation Satellite System (GNSS) velocity data assuming slip‐response functions for an elastic medium. The observed surface velocities, however, include effects of viscoelastic relaxation in the asthenosphere caused by slip motion associated with seismic cycles. If the elastic responses cannot adequately approximate the deformation of the viscoelastic medium, the results of an inversion analysis could be biased. If the recurrence interval is greater than the effective relaxation time in the elastic‐viscoelastic layered structure, we were able to formulate an inverse problem for the estimation of slip‐deficit rates from GNSS velocity data with completely relaxed slip‐response functions for a later stage of the seismic cycle. Analyzing surface velocity data from GNSS daily coordinate data between March 2005 and February 2011 together with seafloor geodetic data, we estimated the slip‐deficit rate distribution by the strain data inversion method. There were significant differences between the results using elastic and completely relaxed responses. Although the result with elastic responses shows a high coupling zone in the coastal region, it was located trenchward when completely relaxed responses were used. We found that the peak slip‐deficit rate increases as the thickness of the lithosphere becomes thinner. Moreover, we succeeded in appropriately separating elastic‐viscoelastic deformation due to plate coupling from rigid block motion.

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“…These simulations can be computationally intensive, because they must include nucleation of ruptures as fault loading increases (e.g., acceleration of slip within a confined zone as a result of loading and rate and state friction [ Tse and Rice , 1986; Okubo , 1989; Dieterich , 1992]). This means that we must have sufficient spatial and temporal resolution to capture the slow buildup of strain and its sudden release in propagating ruptures (so that the modeling incorporates 3‐D effects known to be important in studying rupture propagation [e.g., Harris , 2004, and references therein] and viscoelastic deformation [e.g., Yoshioka and Suzuki , 1999; Freed and Lin , 2001; Wang et al , 2001; Hearn et al , 2002]). As these multicycle models become more comprehensive and approach the complexity necessary to provide additional constraints on fault constitutive models, the number of small events generated on the fault system will tend to increase in accordance with the Gutenberg‐Richter frequency‐magnitude relationship.…”

Section: Discussionmentioning

confidence: 99%

Constraining fault constitutive behavior with slip and stress heterogeneity

Aagaard

Heaton

2008

J. Geophys. Res.

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[1] We study how enforcing self-consistency in the statistical properties of the preshear and postshear stress on a fault can be used to constrain fault constitutive behavior beyond that required to produce a desired spatial and temporal evolution of slip in a single event. We explore features of rupture dynamics that (1) lead to slip heterogeneity in earthquake ruptures and (2) maintain these conditions following rupture, so that the stress field is compatible with the generation of aftershocks and facilitates heterogeneous slip in subsequent events. Our three-dimensional finite element simulations of magnitude 7 events on a vertical, planar strike-slip fault show that the conditions that lead to slip heterogeneity remain in place after large events when the dynamic stress drop (initial shear stress) and breakdown work (fracture energy) are spatially heterogeneous. In these models the breakdown work is on the order of MJ/m 2 , which is comparable to the radiated energy. These conditions producing slip heterogeneity also tend to produce narrower slip pulses independent of a slip rate dependence in the fault constitutive model. An alternative mechanism for generating these confined slip pulses appears to be fault constitutive models that have a stronger rate dependence, which also makes them difficult to implement in numerical models. We hypothesize that self-consistent ruptures could also be produced by very narrow slip pulses propagating in a self-sustaining heterogeneous stress field with breakdown work comparable to fracture energy estimates of kJ/M 2 .Citation: Aagaard, B. T., and T. H. Heaton (2008), Constraining fault constitutive behavior with slip and stress heterogeneity,

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Effects of Three-dimensional Inhomogeneous Viscoelastic Structures on Postseismic Surface Deformations Associated with the Great 1946 Nankaido Earthquake

Cited by 14 publications

References 29 publications

Spectral finite element approach to postseismic deformation in a viscoelastic self-gravitating spherical Earth

Spectral finite element approach to postseismic deformation in a viscoelastic self-gravitating spherical Earth

Slip‐Deficit Rate Distribution Along the Nankai Trough, Southwest Japan, With Elastic Lithosphere and Viscoelastic Asthenosphere

Constraining fault constitutive behavior with slip and stress heterogeneity

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