Importance of horizontal seafloor motion on tsunami height for the 2011 Mw=9.0 Tohoku-Oki earthquake

Hooper, Andrew; Pietrzak, Julie D.; Simons, Wim; Cui, H.; Riva, Riccardo; Naeije, Marc; Scheltinga, A. Terwisscha van; Schrama, Ernst; Stelling, Guus S.; Socquet, Anne

doi:10.1016/j.epsl.2012.11.013

Cited by 78 publications

(91 citation statements)

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“…The need for a realistic ocean becomes increasingly important when lower truncation degrees are chosen or additional smoothing is applied as longer wavelength gravity signals are more prone to continent-ocean transitions. An identical numerical experiment is performed for three forward models for the 2011 Tohoku-Oki earthquake (Hayes 2011;Wei et al 2011;Hooper et al 2013). Depending on the slip model chosen, the experiment revealed more modest geoid height changes due to an inclusion of a realistic ocean.…”

Section: Discussionmentioning

confidence: 99%

“…As discussed by Hooper et al (2013), the effect of horizontal motion on water column height becomes more important for shallow slip. Therefore, we study the sensitivity of coseismic gravity changes for horizontal motion with increasing slip depth, where we adopt the fault geometry of Hooper et al (2013):…”

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%

“…Horizontal displacement of a steeply sloping ocean floor likely contributed to about half of the water column uplift after the 2011 Tohoku event as shown by Hooper et al (2013). Horizontal displacements thus potentially contribute to gravity changes as well.…”

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confidence: 95%

“…9. Hooper et al (2013) show that approximately half of the peak amplitude of the tsunami following the 2011 TohokuOki earthquake can be explained from bathymetry changes due to horizontal movement of the steep ocean floor. Likewise, the effect of horizontal motion of sloped ocean floors changes the height of the water column that should be taken into account for modelling seismic gravity changes.…”

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%

“…The same test has been applied for the Tohoku-Oki earthquake and Sumatra-Andaman earthquake where running the sea level equation at l max = 40 leads to errors in coseismic geoid negative and positive peak values of −14(/+48) per cent [Wei et al (2011) slip model], −28 per cent/+100 per cent [Hayes (2011) slip model], −24(/+42) per cent [Hooper et al (2013) slip model] and 0 per cent/+12 per cent [Chlieh et al (2007) Sumatra-Andaman slip model]. When a slip model results in a very small absolute amplitude of the positive pole the errors are given in between brackets.…”

Section: Signal Loss Due To Truncation At Low Degree Spherical Harmonicsmentioning

confidence: 99%

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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: Discussionmentioning

confidence: 99%

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%

mentioning

confidence: 95%

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%

Section: Signal Loss Due To Truncation At Low Degree Spherical Harmonicsmentioning

confidence: 99%

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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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A decadal‐scale deformation transient prior to the 2011 M_w 9.0 Tohoku‐oki earthquake

Mavrommatis

Segall

Johnson

2014

Geophysical Research Letters

134

166

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GPS time series in northeast Japan exhibit nonlinear trends from 1996 to 2011 before the Mw 9.0, 2011 Tohoku‐oki earthquake. After removing reference frame noise, we model time series as linear trends plus constant acceleration, correcting for coseismic and postseismic effects from the numerous Mw ∼ 6.5+ earthquakes during this period. We find spatially coherent and statistically significant accelerations throughout northern Honshu. Large areas of Japan outside the Tohoku region show insignificant accelerations, demonstrating that the observation is not due to network‐wide artifacts. While the accelerations in northern Tohoku (Sanriku area) can be explained by decaying postseismic deformation from pre‐1996 earthquakes, the accelerations in south‐central Tohoku appear unrelated to postseismic effects. The latter accelerations are associated with a decrease in average trench‐normal strain rate and can be explained by increasing slip rate on the Japan trench plate interface and/or updip migration of deep aseismic slip in the decades before the 2011 Tohoku‐oki earthquake.

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Broadscale postseismic gravity change following the 2011 Tohoku‐Oki earthquake and implication for deformation by viscoelastic relaxation and afterslip

Han

Sauber

Pollitz

2014

Geophysical Research Letters

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The analysis of GRACE gravity data revealed postseismic gravity increase by 6 μGal over a 500 km scale within a couple of years after the 2011 Tohoku-Oki earthquake, which is nearly 40–50% of the coseismic gravity change. It originates mostly from changes in the isotropic component corresponding to the Mrr moment tensor element. The exponential decay with rapid change in a year and gradual change afterward is a characteristic temporal pattern. Both viscoelastic relaxation and afterslip models produce reasonable agreement with the GRACE free-air gravity observation, while their Bouguer gravity patterns and seafloor vertical deformations are distinctly different. The postseismic gravity variation is best modeled by the biviscous relaxation with a transient and steady state viscosity of 1018 and 1019 Pa s, respectively, for the asthenosphere. Our calculated higher-resolution viscoelastic relaxation model, underlying the partially ruptured elastic lithosphere, yields the localized postseismic subsidence above the hypocenter reported from the GPS-acoustic seafloor surveying.

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Importance of horizontal seafloor motion on tsunami height for the 2011 Mw=9.0 Tohoku-Oki earthquake

Cited by 78 publications

References 40 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

A decadal‐scale deformation transient prior to the 2011 M_w 9.0 Tohoku‐oki earthquake

Broadscale postseismic gravity change following the 2011 Tohoku‐Oki earthquake and implication for deformation by viscoelastic relaxation and afterslip

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Importance of horizontal seafloor motion on tsunami height for the 2011 Mw=9.0 Tohoku-Oki earthquake

Cited by 78 publications

References 40 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

A decadal‐scale deformation transient prior to the 2011 Mw 9.0 Tohoku‐oki earthquake

Broadscale postseismic gravity change following the 2011 Tohoku‐Oki earthquake and implication for deformation by viscoelastic relaxation and afterslip

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A decadal‐scale deformation transient prior to the 2011 M_w 9.0 Tohoku‐oki earthquake