Equipartitioning is not sufficient for Green’s function extraction

Snieder, Roel; Fan, Y.; Slob, Evert; Wapenaar, Kees

doi:10.1007/s11589-010-0739-1

Cited by 27 publications

(20 citation statements)

References 58 publications

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“…[2009] found that near‐vertical reflections can be constructed by correlating wavefields that contain signals with sufficiently small slowness. Indeed, the under‐estimation of body waves has been pointed out if both noise sources and stations are distributed at the ground surface [ Forghani and Snieder , ; Snieder et al ., ].…”

Section: Discussionmentioning

confidence: 99%

A temporal change of shear wave anisotropy within the marine sedimentary layer associated with the 2011 Tohoku‐Oki earthquake

et al. 2013

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[1] We found persistent reflections of S waves from the bottom of a $350 m thick marine sedimentary layer on the outer rise of the Japan Trench, just to the east of the source area of the 2011 great Tohoku-Oki earthquake (Mw9.0), by auto-correlating ambient seismic noise recorded on 1 year continuous records of broadband ocean bottom seismometers. The two-way travel times of reflected S waves, which vary as a function of the polarization direction, indicate a velocity anisotropy of~1.7% in the sedimentary layer. The fast direction is estimated to be trench parallel, possibly due to cracks or normal faults formed by bending of the plate in the outer rise. The travel time also shows a coseismic velocity reduction of~2%, with slightly reduced anisotropy, within the layer. The change gradually recovered to pre-earthquake conditions through 4 months after the earthquake, although recovery was not complete during the period of the observation. We also detected a similar anisotropic structure and magnitude of coseismic velocity reduction in this layer based on S coda of earthquakes with magnitudes greater than 5.0. Such coseismic changes can be explained either by increases of crack density and crack sphericity within the suddenly stressed sedimentary layer or by channeling and networking of water flow in the strongly shaken sedimentary layer.

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Section: Discussionmentioning

confidence: 99%

A temporal change of shear wave anisotropy within the marine sedimentary layer associated with the 2011 Tohoku‐Oki earthquake

et al. 2013

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“…For a direct noise crosscorrelation to yield the Green's function, we require the ambient seismic field to be in a state of energy equipartitioning . However, that state is not sufficient, we also require all noise sources to act incoherently (Snieder et al, 2010). Under ideal circumstances, the crosscorrelation signal yields an equivalence of the superposition of the causal Green's function and its anticausal reciprocal counterpart, forming a purely symmetric signal.…”

Section: Passive Seismic Interferometrymentioning

confidence: 99%

Ambient seismic noise tomography at Ekofisk

Ridder

Biondi

2015

GEOPHYSICS

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We have studied an approximately 40-hr recording from the Life of Field Seismic array installed over Ekofisk field to assess whether the recorded ambient seismic energy was suitable for passive seismic surface-wave interferometry. Passive seismic interferometry aims to retrieve virtual seismic sources by crosscorrelation. We have found that the noise recorded by the pressure sensors between 0.4 and 1.4 Hz consisted predominantly of Scholte-wave microseism energy. The noise incidence directions have an almost uniform distribution over the azimuth, enabling the synthesis of nearly symmetric estimated Green's functions between all stations in the array that formed virtual seismic sources. These sources were dominated by Scholte waves traveling along the seafloor, and we sought to determine which features in the subsurface can be imaged by straight-ray group-velocity tomography. We located a high-velocity anomaly in the center of Ekofisk's production-induced subsidence bowl, surrounded by lower velocities. This pattern seemed to result from production-induced seafloor subsidence that altered the near-surface shear strengths. A dispersion analysis showed that the Scholtewave virtual seismic source exhibited an approximate penetration depth to 600 m below the seafloor. These results are significant because they demonstrated that recordings made at the oceanbottom cable array at Ekofisk field in the absence of seismic shooting can be used to image and monitor the near surface.

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“…For many cases, equipartitioning is not sufficient for Green's function extraction (Snieder et al, 2010). On the other hand, in some practical cases, for example passive seismic imaging, estimated Green's function can be extracted even when the equipartition is not fully satisfied (Mulargia and Castellaro, 2008;Perton et al, 2009).…”

Section: Conclusion and Discussionmentioning

confidence: 99%

“…Therefore, if one just retrieves the estimated Green's function, equipartitioning is not sufficient, and it may even not necessary. Snieder et al (2010) gave examples that equipartitioning was not sufficient. We can explore that equipartitioning is not necessary by addressing Eq.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Retrieval of Green’s function and generalized optical theorem for the scattering of complete dyadic fields

Ding

Zeng

et al. 2011

The Journal of the Acoustical Society of America

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Green's function retrieval has been widely used in different research fields due to the fact that the Green's function can be extracted by cross-correlating the records at two receivers. In this paper, the retrieval of the dyadic Green's function is studied by investigating the representation theorem. The generalized optical theorem for the dyadic fields is derived based on the elastic dynamic interferometric equation. By addressing the cross-correlation recorded at two receivers, the important role of the generalized optical theorem and energy equipartition in retrieving the exact Green's function is shown. The presented derivation also shows the Newton-Marchenko equation holdsif the condition of equipartition is not satisfied.

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Equipartitioning is not sufficient for Green’s function extraction

Cited by 27 publications

References 58 publications

A temporal change of shear wave anisotropy within the marine sedimentary layer associated with the 2011 Tohoku‐Oki earthquake

A temporal change of shear wave anisotropy within the marine sedimentary layer associated with the 2011 Tohoku‐Oki earthquake

Ambient seismic noise tomography at Ekofisk

Retrieval of Green’s function and generalized optical theorem for the scattering of complete dyadic fields

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