Elliptical‐anisotropic eikonal phase velocity tomography

Ridder, Sjoerd A. L. de; Biondi, Biondo; Nichols, David M.

doi:10.1002/2014gl062805

Cited by 21 publications

(27 citation statements)

References 26 publications

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“…Similar anomalies have been found at Valhall field from critically reflected P-waves (Hatchell et al, 2009). Weakening of the shear strength in the radial directions with respect to the center of the subsidence bowl also causes strong azimuthal anisotropy in surface-wave phase velocities over Ekofisk field (De Ridder et al, 2015).…”

Section: A) B) C)mentioning

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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Section: A) B) C)mentioning

confidence: 99%

Ambient seismic noise tomography at Ekofisk

Ridder

Biondi

2015

GEOPHYSICS

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“…Their results fitted well with their seismically derived compaction map (which does not show the center of the array due to there being a seismically obscured area in the center of the array). The ringed structure of the velocity and Q at the Ekofisk array can also be observed in surface wave group velocity tomography (de Ridder et al, ; de Ridder & Biondi, ), surface wave phase velocity tomography (de Ridder & Biondi, ; de Ridder & Curtis, ), and compressional and shear wave velocity (Kazinnik et al, ) estimates at the site.…”

Section: Geological Interpretationmentioning

confidence: 86%

Seismic Attenuation From Ambient Noise Across the North Sea Ekofisk Permanent Array

et al. 2018

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Quality factor (Q) or equivalently attenuation α=1Q describes the amount of energy lost per cycle as a wave travels through a medium. This is important to correct seismic data amplitudes for near‐surface effects, to locate subsurface voids or porosity, to aid seismic interpretation, or for characterizing other rock and fluid properties. Seismic attenuation can be variable even when there are no discernible changes in seismic velocity or density (Yıldırım et al., 2017, https://doi.org/10.1016/j.jappgeo.2016.11.010) and so provides independent information about subsurface heterogeneity. This study uses ambient noise recordings made on the Ekofisk Life of Field Seismic array to estimate Q structure in the near surface. We employ the method of X. Liu et al. (2015, https://doi.org/10.1093/gji/ggv357), which uses linear triplets of receivers to estimate Q—ours is the first known application of the method to estimate the Q structure tomographically. Estimating Q requires an estimate of phase velocity which we obtain using the method of Bloch and Hales (1968, https://pubs.geoscienceworld.org/ssa/bssa/article-abstract/58/3/1021/116607/) followed by traveltime tomography. The Q structure at Ekofisk has features which can be related to local geology, showing that surface ambient noise recordings may provide a new and robust method to image Q. Our results suggest that there is a nonlinear relationship between Q and compression. They also may explain why it has been found that in the period range of 1 to 2 s considered here, ambient noise cross correlations along paths that span the North Sea Basin are unreliable: Such Q values would attenuate almost all ambient seismic energy during such a traverse.

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“…The success of these studies has encouraged investigation of this technique at the exploration scale. In ocean-bottom environments, de Ridder et al (2014) and Mordret et al (2014) obtained reliable time-lapse group and phase velocity maps, respectively, of the Valhall overburden, while de Ridder et al (2015) recovered phase velocity and anisotropy maps representative of subsidence patterns at Ekofisk. In these cases, the examined frequencies were less than 2 Hz.…”

Section: Introductionmentioning

confidence: 90%

Rayleigh-wave tomography using traffic noise at Long Beach, CA

Chang

Biondi

2015

SEG Technical Program Expanded Abstracts 2015

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Passive seismic arrays on land provide the opportunity to push the use of ambient noise cross-correlation techniques to frequencies well beyond the microseism band. Using data recorded by a dense array in Long Beach, California, we demonstrate that high-frequency (> 3 Hz) fundamental-and first-order-mode Rayleigh waves generated by traffic noise can be extracted from the ambient noise field and used for tomographic studies. Here, we show group velocity maps derived from travel times of the fundamental-mode Rayleigh waves at 3.00 Hz and 3.50 Hz. The velocity trends in our results correlate well with lithologies outlined in a geologic map of the survey region. As expected, less-consolidated materials display relatively low velocities, while more-consolidated materials display relatively high velocities.

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Elliptical‐anisotropic eikonal phase velocity tomography

Cited by 21 publications

References 26 publications

Ambient seismic noise tomography at Ekofisk

Ambient seismic noise tomography at Ekofisk

Seismic Attenuation From Ambient Noise Across the North Sea Ekofisk Permanent Array

Rayleigh-wave tomography using traffic noise at Long Beach, CA

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