Heterogeneous rheology controlled postseismic deformation of the 2011 Tohoku‐Oki earthquake

Muto, Jun; Shibazaki, Bunichiro; Iinuma, Toshitaka; Ito, Yoshihiro; Ohta, Yusaku; Miura, Satoshi; Nakai, Yoshihiko

doi:10.1002/2016gl068113

Cited by 44 publications

(59 citation statements)

References 34 publications

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“…Small-scale rheological heterogeneities across the arc, such as a weak volcanic front and a strong forearc, contribute to local deformation, as reported by Muto et al (2016); however, their modeling is based on a 2D profile. On close examination of the residuals of displacement in our model (Fig.…”

Section: Assessment Of Viscoelastic Structurementioning

confidence: 97%

Importance of rheological heterogeneity for interpreting viscoelastic relaxation caused by the 2011 Tohoku-Oki earthquake

Suito

2017

Earth Planets Space

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This study develops a three-dimensional viscoelastic model using the finite element method to understand the postseismic deformation that followed the 2011 Tohoku-Oki earthquake. The question of understanding which elements of the viscoelastic media affect the surface deformation is of particular importance. We first examined the individual effects of two different viscoelastic media, the mantle wedge and the oceanic mantle, which produce almost opposite deformation patterns. The mantle wedge controls eastward motion, uplift of the Pacific coastal and offshore regions, and extension across a broad area. In contrast, the oceanic mantle controls dominantly offshore westward motion, subsidence across a broad area, minor uplift of the surrounding areas, and contraction offshore. These differences are the most important issues for understanding the viscoelastic relaxation caused by subduction earthquakes. We then developed four different models to clarify which elements of the viscoelastic media affect the observed surface deformation. The simplest model, with uniform viscosity for all viscoelastic media, could explain the horizontal deformation but not the vertical deformation. The second model, with different viscosities for the mantle wedge and the oceanic mantle, could explain the onshore observations but could not explain the seafloor observations. The third model, which includes a thin weak layer beneath the subducting slab, could essentially explain the near-field onshore and seafloor observations but could not explain the far-field data. The final depth-dependent model was able to explain the far-field data as well as the near-field data. In these typical models, it is of particular importance to consider the different viscosities between the mantle wedge and the oceanic mantle and to include a thin weak layer beneath the slab, which has a dramatic impact on the seafloor deformation. Far-field data as well as near-field data are also important for constraining the viscoelastic structure; the former is sensitive to viscoelastic relaxation at greater depths. Clearly, viscoelastic relaxation alone cannot explain the observed deformation. A combined viscoelastic and afterslip model is necessary for constructing a complete postseismic deformation model.

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Section: Assessment Of Viscoelastic Structurementioning

confidence: 97%

Importance of rheological heterogeneity for interpreting viscoelastic relaxation caused by the 2011 Tohoku-Oki earthquake

Suito

2017

Earth Planets Space

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“…However, I assume a large water content C OH = 10,000 ppm H/Si in the mantle wedge corner up to 400 km away from the trench, associated with the dehydration of peridotite and arc volcanism, and a damped water content of C OH = 1,000 ppm H/Si elsewhere (Figure 1). I also ignore the low-viscosity region below the volcanic arc (Hu et al, 2014;Muto et al, 2016) as it mainly affects the vertical displacement in the near field. This is obviously a simplification, but it reflects how the remaining uncertainties on the mantle wedge rheology still limit our understanding of this important region.…”

Section: Subduction Dynamics With the Integral Methodsmentioning

confidence: 99%

Asthenosphere Flow Modulated by Megathrust Earthquake Cycles

Barbot

2018

Geophysical Research Letters

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Subduction megathrusts develop the largest earthquakes, often close to large population centers. Understanding the dynamics of deformation at subduction zones is therefore important to better assess seismic hazards. Here I develop consistent earthquake cycle simulations that incorporate localized and distributed deformation based on laboratory‐derived constitutive laws by combining boundary and volume elements to represent the mechanical coupling between megathrust slip and solid‐state flow in the oceanic asthenosphere and in the mantle wedge. The model is simplified, in two dimensions, but may help the interpretation of geodetic data. Megathrust earthquakes and slow‐slip events modulate the strain rate in the upper mantle, leading to large variations of effective viscosity in space and time and a complex pattern of surface deformation. While fault slip and flow in the mantle wedge generate surface displacements in the same, that is, seaward, direction, the viscoelastic relaxation in the oceanic asthenosphere generates transient surface deformation in the opposite, that is, landward, direction above the rupture area of the mainshock. Aseismic deformation above the seismogenic zone may be challenging to record, but it may reveal important constraints about the rheology of the subducting plate.

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“…However, there exists a significant systematic discrepancy between the actual structure and our structure model (a standard elastic-viscoelastic layered half-space model), which will cause a bias in the estimation of afterslip distribution. As demonstrated by Muto et al (2016), for example, the vertical components are much sensitive to the structural discrepancy in comparison with the horizontal components, and so we did not use the vertical components in the present analysis.…”

Section: Gps Time-series Datamentioning

confidence: 99%

Interpretation of Offshore Crustal Movements Following the 2011 Tohoku-Oki Earthquake by the Combined Effect of Afterslip and Viscoelastic Stress Relaxation

Noda

Kawasato

Matsu’ura

2017

Pure Appl. Geophys.

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Abstract-On the 11th March 2011, a megathrust event, called the Tohoku-oki earthquake, occurred at the North American-Pacific plate interface off northeast Japan. Transient crustal movements following this earthquake were clearly observed by a dense GPS network (GEONET) on land and a sparse GPS/Acoustic positioning network on seafloor. The observed crustal movements are in accordance with ordinary expectations on land, but not on seafloor; that is, slowly decaying landward movements above the main rupture area and rapidly decaying trench-ward movements in its southern extension. To reveal the cause of such curious offshore crustal movements, we analyzed the coseismic and postseismic GPS array data on land with a sequential stepwise inversion method considering viscoelastic stress relaxation in the asthenosphere, and obtained the following results: The afterslip of the Tohoku-oki earthquake rapidly proceeds for the first 1 year on a high-angle downdip extension of the main rupture, which occurred on the low-angle offshore plate interface. The theoretical patterns of seafloor horizontal movements due to the afterslip and the viscoelastic relaxation of coseismic stress changes in the asthenosphere are essentially different both in space and time; inshore trench-ward movements and offshore landward movements for the afterslip, while overall landward movements for the viscoelastic stress relaxation. General agreement between the computed horizontal movements and the GPS/Acoustic observations demonstrates that the postseismic curious offshore crustal movements can be ascribed to the combined effect of afterslip on a high-angle downdip extension of the main rupture and viscoelastic stress relaxation in the asthenosphere.

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Heterogeneous rheology controlled postseismic deformation of the 2011 Tohoku‐Oki earthquake

Cited by 44 publications

References 34 publications

Importance of rheological heterogeneity for interpreting viscoelastic relaxation caused by the 2011 Tohoku-Oki earthquake

Importance of rheological heterogeneity for interpreting viscoelastic relaxation caused by the 2011 Tohoku-Oki earthquake

Asthenosphere Flow Modulated by Megathrust Earthquake Cycles

Interpretation of Offshore Crustal Movements Following the 2011 Tohoku-Oki Earthquake by the Combined Effect of Afterslip and Viscoelastic Stress Relaxation

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