Crustal Dilatation Observed by GRACE After the 2004 Sumatra-Andaman Earthquake

Han, Shin‐Chan; Shum, C. K.; Bevis, Michael; Ji, Chen; Kuo, Chung-Yen

doi:10.1126/science.1128661

Cited by 299 publications

(311 citation statements)

References 13 publications

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“…This means that the sea level is no longer self-consistent as no deformation due to change in water load or self-gravitation of the ocean is taken into account and water mass is no longer conserved. This resembles the approach used by for example Han et al (2006) (who used a half-space model that also neglects the Earth's sphericity), Heki & Matsuo (2010) and Matsuo & Heki (2011) (while these authors also neglect the ocean-land division). The authors include the ocean effect by using the difference in water and crustal densities for calculating the effect of topography change on gravity.…”

Section: Effects Of Loading Self-gravitation and Conservation Of Ocementioning

confidence: 99%

“…Since the occurrence of the M w 9.1 2004 Sumatra-Andaman earthquake, a number of studies extracted the coseismic gravity change from the GRACE data and compared it with model results (e.g. Han et al 2006;Ogawa & Heki 2007;de Linage et al 2009), usually based on seismological or land-based geodetic data. While smaller in magnitude, the M w 8.8 Maule (Chile) earthquake produced sufficiently large mass displacements to be detected by GRACE, as demonstrated by Heki & Matsuo (2010) and Han et al (2010).…”

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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: Effects Of Loading Self-gravitation and Conservation Of Ocementioning

confidence: 99%

mentioning

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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“…Изменение поля силы тяжести во время Суматринского землетрясения 2004 г. [Han et al, 2006]. Синим показано уменьшение, красным -увеличение.…”

Section: особенности кинематики зоны субдукции свидетельствующие о рunclassified

Seismic nails in various geodynamic conditions

Захаров

Карпенко

Zav’yalov

2013

Moscow Univ. Geol. Bull.

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An earthquake source is characterized by two nodal planes oriented parallel to two planes of maximum shear stresses ( Fig. 1, left). A rapid displacement of the shear type (in mechanical, rather than in the geological meaning) occurs along one of the planes and causes an earthquake.The concept of plate tectonics with one of its main components, subduction zones, provides, at first sight, the unique opportunity to select one of the two nodal planes -a gently dipping plane which is parallel to the roof of the subducting oceanic plate (Fig. 1, bottom right). The other nodal plane that is steeply dipping in the opposite direction (Fig. 1, top right) seems 'unpromising', considering the aspect of seismicity, for two reasons. First, displacement along this plate is contrary to the general direction of oceanic plate subduction. Secondly, such displacement is directed against the direction of gravity, which is energetically disadvantageous.However, it should be taken into account that in the stress field of the subduction zone, as in any stress field, the two above-mentioned maximum shear stresses have equal values. At the same time, it is the sub-vertical displacement that excites rapid uplifting of the seabed which causes a tsunami. Researchers who support the traditional choice of a gently dipping nodal plane have to reckon with it and therefore create complex models, such as the 'splay fault' model that seem most successful, though being quite complicated and controversial (Figs. 56 and 57).In our opinion, the geological reality is more adequately refelected by the geological and geophysical model shown in Fig. 1 (right). It is based on the wide range of information and assumes that both nodal planes are equivalent and interchange in generation of strong earthquakes.The aim of this article is to consider this model in terms of tectonophysics. For this purpose, earthquake sources indicated on (Fig. 1, right) are classified as Riedel megashears, R (bottom right) and R' (top right top), which occur in the geodynamic setting of sub-horizontal shearing (in this case, subduction of the oceanic plate) along the sub-horizontal plane (Fig. 3). This situation is one of five elementary geodynamic settings (see Fig. 2). It is similar in everything, except the position of the shearing plane, with the geodynamic setting of horizontal shearing along the vertical plane (Fig. 4). Riedel shears formed in the latter situation were subject to the most detailed studies using purpose-made devices (Fig. 5, and 6). This study gave grounds to conclude that Riedel shears, R are developed much better than shears R'.Our experiments (Fig. 7) confirm the above conclsuion. Moreover, it is revealed that shears R', that develop poorly in samples made of wet clay (Figs. 8, 9, 12, and 13), cannot develop in a granulated medium such as a mixture of sand and solid oil (Fig. 10, 11, and 14) and do not develop in other granulated media (Fig. 17), which are similar to the block structure of the uppermost crust (Fig. 18-20). In such mediums, shea...

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“…This formalism thus aims at improving our understanding of the relation between the static perturbation and the whole fault system, and to make easier the implementation of spherically symmetric Earth models in geodetic problems, like the modelling of long-wavelength gravity or geoid anomalies, nowadays detectable by Gravity Recovery and Climate Experiment (GRACE) and Gravity field and steady-state Ocean Circulation Explorer (GOCE) space missions (Han et al, 2006;Panet et al, 2007;de Linage et al, 2009, Cambiotti et al, 2011Matsuo and Heki, 2011;Han et al, 2011;Wang et al, 2012;Sabad ini, 2012, 2013;Fuchs et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

On the response of the Earth to a fault system: its evaluation beyond the epicentral reference frame

Cambiotti

Sabadini

2015

Geophys. J. Int.

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SUMMARYPrevious formalisms for determining the static perturbation of spherically symmetric selfgravitating elastic Earth models due to displacement dislocations deal with each infinitesimal element of the fault system in its epicentral reference frame. In this work we overcome this restriction and present novel and compact formulas for obtaining the perturbation due to the whole fault system in an arbitrary and common reference frame. Furthermore, we show that, even in an arbitrary reference frame, it is still possible to discriminate the contributions associated to the polar, bipolar and quadrupolar patterns of the seismic source response, as well as their relation with the along strike, along dip and tensile components of the displacement dislocation. These results allow a better understanding of the relation between the static perturbation and the whole fault system, and find direct applications in geodetic problems, like the modelling of long-wavelength geoid or gravity data from GRACE and GOCE space missions and of the perturbation of the deviatoric inertia tensor of the Earth.

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Crustal Dilatation Observed by GRACE After the 2004 Sumatra-Andaman Earthquake

Cited by 299 publications

References 13 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

Seismic nails in various geodynamic conditions

On the response of the Earth to a fault system: its evaluation beyond the epicentral reference frame

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