Frontal wedge deformation near the source region of the 2011 Tohoku-Oki earthquake

Ito, Yoshihiro; Tsuji, Takeshi; Osada, Yoshihito; Kido, Motoyuki; Inazu, Daisuke; Hayashi, Yutaka; Tsushima, Hiroaki; Hino, Ryota; Fujimoto, Hiromi

doi:10.1029/2011gl048355

Cited by 257 publications

(217 citation statements)

References 16 publications

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“…The contribution of horizontal motion to the change in bathymetry will increase when the gradient of the bathymetry is larger or when the horizontal component of deformation becomes larger with respect to the vertical component. Especially the large horizontal displacements caused by the Tohoku-Oki earthquake-more than 50 m displacement has been observed (Ito et al 2011)-explain the large contribution of horizontal displacement to gravity, compared to the Sumatra-Andaman and Maule cases, for which we have modelled up to 10.1 and 5.8 m of horizontal displacement (at l max = 450).…”

Section: E F F E C T O F H O R I Z O N Ta L D I S P L a C E M E N T Omentioning

confidence: 99%

Ocean contribution to seismic gravity changes: the sea level equation for seismic perturbations revisited

Broerse¹,

Riva²,

Vermeersen³

2014

Geophysical Journal International

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S U M M A R YDuring megathrust earthquakes, great ruptures are accompanied by large scale mass redistribution inside the solid Earth and by ocean mass redistribution due to bathymetry changes. These large scale mass displacements can be detected using the monthly gravity maps of the GRACE satellite mission. In recent years it has become increasingly common to use the long wavelength changes in the Earth's gravity field observed by GRACE to infer seismic source properties for large megathrust earthquakes. An important advantage of space gravimetry is that it is independent from the availability of land for its measurements. This is relevant for observation of megathrust earthquakes, which occur mostly offshore, such as the M w ∼ 9 2004 Sumatra-Andaman, 2010 Maule (Chile) and 2011 Tohoku-Oki (Japan) events. In Broerse et al., we examined the effect of the presence of an ocean above the rupture on long wavelength gravity changes and showed it to be of the first order.Here we revisit the implementation of an ocean layer through the sea level equation and compare the results with approximated methods that have been used in the literature. One of the simplifications usually lies in the assumption of a globally uniform ocean layer. We show that especially in the case of the 2010 Maule earthquake, due to the closeness of the South American continent, the uniform ocean assumption is not valid and causes errors up to 57 per cent for modelled peak geoid height changes (expressed at a spherical harmonic truncation degree of 40). In addition, we show that when a large amount of slip occurs close to the trench, horizontal motions of the ocean floor play a mayor role in the ocean contribution to gravity changes. Using a slip model of the 2011 Tohoku-Oki earthquake that places the majority of slip close to the surface, the peak value in geoid height change increases by 50 per cent due to horizontal ocean floor motion. Furthermore, we test the influence of the maximum spherical harmonic degree at which the sea level equation is performed for sea level changes occurring along coastlines, which shows to be important for relative sea level changes occurring along the shore. Finally, we demonstrate that ocean floor loading, self-gravitation of water and conservation of water mass are of second order importance for coseismic gravity changes.When GRACE observations are used to determine earthquake parameters such as seismic moment or source depth, the uniform ocean layer method introduces large biases, depending on the location of the rupture with respect to the continent. The same holds for interpreting shallow slip when horizontal motions are not properly accounted for in the ocean contribution. In both cases the depth at which slip occurs will be underestimated.

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Section: E F F E C T O F H O R I Z O N Ta L D I S P L a C E M E N T Omentioning

confidence: 99%

Ocean contribution to seismic gravity changes: the sea level equation for seismic perturbations revisited

Broerse¹,

Riva²,

Vermeersen³

2014

Geophysical Journal International

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“…Several seismological, geodetic, and tsunami wave inversion studies indicate a large magnitude of coseismic slip (30-60 m) occurred on the shallow portions of the plate boundary [e.g., Ide et al, 2011;Yokota et al, 2011;Fujii et al, 2011;Koketsu et al, 2011]. Differential bathymetric and seafloor geodetic studies [Fujiwara et al, 2011;Sato et al, 2011;Ito et al, 2011] also document large coseismic displacement near the trench. Thus, it is important to understand the detailed structure of the shallow portion of the subduction zone and the trench axis area of the Japan Trench to evaluate mechanisms of deformation and the geometry of the structures that accommodate shallow slip.…”

Section: Introductionmentioning

confidence: 99%

High‐resolution seismic imaging in the Japan Trench axis area off Miyagi, northeastern Japan

Nakamura

Kodaira

Miura

et al. 2013

Geophysical Research Letters

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Newly obtained high‐resolution seismic data reveal the detailed structure of the Japan Trench axis off Miyagi, Japan, in the region of large shallow slip during the 11 March 2011 M9 Tohoku earthquake. Correlation of seismic images with previous drilling results identifies a possible basal chert‐rich layer and hemipelagic/pelagic mudstones overlying igneous Pacific crust. Mapping of acoustic basement depicts the subduction of horst‐and‐graben topography. The basement and basal chert are subducted beneath a seismically chaotic frontal prism, but the majority of overlying hemipelagic mudstones is offscraped and imbricated at the trench axis as a result of plate boundary compression. A possible décollement is imaged as a seaward dipping reflection at landward part of the trench graben and was likely generated by loading and failure of underthrust sediments. Collectively, these analyses provide a structural framework for understanding sedimentary inputs and the localization of shallow plate boundary slip at the Japan Trench.

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“…Most of the plate convergence is accommodated by this feature, which eventually becomes the location of megathrust earthquakes. However, although large magnitude earthquakes cannot nucleate at shallow depths, coseismic slip can propagate all the way to the trench as evidenced by the 2011 M w ¼ 9.0 Tohoku earthquake [Ito et al, 2011;Kodaira et al, 2012]. Large slip in the proximity of the trench is also known to generate very large tsunamis, even if the rupture is slower than usual [Polet and Kanamori, 2000].…”

Section: Introductionmentioning

confidence: 99%

Shear strength of sediments approaching subduction in the Nankai Trough, Japan as constraints on forearc mechanics

Ikari

Hüpers

Kopf

2013

Geochem Geophys Geosyst

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[1] The mechanical behavior of the plate boundary fault zone is of paramount importance in subduction zones, because it controls megathrust earthquake nucleation and propagation as well as the structural style of the forearc. In the Nankai area along the NanTroSEIZE (Kumano) drilling transect offshore SW Japan, a heterogeneous sedimentary sequence overlying the oceanic crust enters the subduction zone. In order to predict how variations in lithology, and thus mechanical properties, affect the formation and evolution of the plate boundary fault, we conducted laboratory tests measuring the shear strengths of sediments approaching the trench covering each major lithological sedimentary unit. We observe that shear strength increases nonlinearly with depth, such that the (apparent) coefficient of friction decreases. In combination with a critical taper analysis, the results imply that the plate boundary position is located on the main frontal thrust. Further landward, the plate boundary is expected to step down into progressively lower stratigraphic units, assisted by moderately elevated pore pressures. As seismogenic depths are approached, the decollement may further step down to lower volcaniclastic or pelagic strata but this requires specific overpressure conditions. High-taper angle and elevated strengths in the toe region may be local features restricted to the Kumano transect.Components: 9,385 words, 7 figures.

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Frontal wedge deformation near the source region of the 2011 Tohoku-Oki earthquake

Cited by 257 publications

References 16 publications

Ocean contribution to seismic gravity changes: the sea level equation for seismic perturbations revisited

Ocean contribution to seismic gravity changes: the sea level equation for seismic perturbations revisited

High‐resolution seismic imaging in the Japan Trench axis area off Miyagi, northeastern Japan

Shear strength of sediments approaching subduction in the Nankai Trough, Japan as constraints on forearc mechanics

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