Offshore ambient-noise surface-wave tomography above 0.1 Hz and its applications

Bussat, Sascha; Kugler, Simone

doi:10.1190/1.3589107

Cited by 36 publications

(21 citation statements)

References 18 publications

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“…One possible explanation of this energy may be that it represents a small fraction of body-wave energy recorded by the array. Bussat and Kugler (2011) observe an acoustically guided wave (P-wave) frequencies as low as 0.6 Hz, but in much deeper waters. Mordret et al (2013a) observe the acoustically guided mode in Valhall OBC recordings, but at greater than 10 Hz.…”

Section: Ambient Seismic Field Recorded By Lofs At Ekofisk Fieldmentioning

confidence: 98%

“…A study of an ocean-bottom-node recording over the Astero field yielded images of group velocities at frequencies between 0.18 and 0.4 Hz, with correlation to known structures (Bussat and Kugler, 2011). Permanently installed OBC ambient noise over Valhall field has yielded images of the near surface using the Scholte-wave group and phase velocities between 0.5 and 1.75 Hz (De Ridder and Dellinger, 2011;De Ridder and Biondi, 2013;Mordret et al, 2013aMordret et al, , 2013bMordret et al, , 2013c.…”

Section: Introductionmentioning

confidence: 99%

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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: Ambient Seismic Field Recorded By Lofs At Ekofisk Fieldmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Ambient seismic noise tomography at Ekofisk

Ridder

Biondi

2015

GEOPHYSICS

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“…The same principle can be applied to surface data or surface-to-crosswell setups (Bussat and Kugler, 2011;de Ridder and Dellinger, 2011).…”

Section: Karaoulis 1 D D Werkema 2 and A Revilmentioning

confidence: 90%

2D time-lapse seismic tomography using an active time-constraint (ATC) approach

2015

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A 2D seismic time-lapse inversion approach can image the evolution of seismic velocities over time and space. The forward modeling is based on solving the eikonal equation using a second-order fast-marching method. Wave paths are represented by Fresnel volumes rather than by conventional rays. This approach accounts for complex velocity models and has the advantage of considering the effects of wave frequency on velocity resolution. The aim of time-lapse inversion is to find changes in velocities of each cell in the model as a function of time. Each model along the time axis is called a reference space model. This approach can be simplified into an inverse problem that seeks the optimum of several reference space models taken together, using the approximation that the change in seismic velocity varies linearly in time between two subsequent reference models. The method is demonstrated on a synthetic example that includes regularization in time in the cost function and reduces inversion artifacts associated with noise in the data by comparison with independent inversions at each time.

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“…It enables seismology to provide high‐resolution tomography studies from local (e.g. Bussat & Kugler 2011) to continental (e.g. Shapiro et al 2005) scale and independent from earthquake seismicity or active seismic sources.…”

Section: Introductionmentioning

confidence: 99%

Performance of different processing schemes in seismic noise cross-correlations

Groos

Bussat

Ritter

2011

Geophysical Journal International

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S U M M A R YThe estimation of the Green's function between two points on the Earth's surface by the crosscorrelation of seismic noise time-series became a widely used method in seismology. In general, very long time-series (months to years) as well as massive normalization and/or data selection are necessary to obtain useful cross-correlation functions. One task of this study is to evaluate the influence of different established normalization methods on the obtained cross-correlation functions. Furthermore, we evaluate two waveform preserving time domain normalizations as well as a new fully automated data selection approach. The cross-correlation functions analysed in this study are obtained from 12 months of seismic noise recorded in 2004 at five seismic stations in the United States with station distances on a continental scale. For practical reasons, the cross-correlation functions of such long time-series are calculated by stacking the cross-correlation functions obtained from shorter time windows. We use this stacking process for the implementation of the waveform preserving time domain normalizations. The time window length is in general an important parameter of the cross-correlation processing, as it influences the normalization and data selection. Therefore, we evaluate the cross-correlation functions obtained with 47 different time window lengths between one hr and 24 hr. The time domain normalizations intend to suppress the influence of transient signals like earthquake waves as well as long-term (e.g. seasonal) amplitude variations. We compare the proposed waveform preserving time domain normalizations with the established running absolute mean normalization and the one-bit normalization. We demonstrate that a waveform preserving time domain normalization can replace a non-linear time domain normalization, if a time window length similar to the duration of the typically occurring transient signals is used. Next to the time domain normalizations also the spectral whitening in the frequency domain is evaluated. Spectral whitening is a powerful normalization to improve the emergence of broadband signals in seismic noise cross-correlations. Nevertheless, we observe spectral whitening to depend strongly on the time window length. An unwanted amplification of a persistent microseism signal is observed on the continental scale with time windows shorter than 12 hr. Our approach of automated data selection is based on a statistical time-series classification and reliably excludes time windows with transient signals occurring contemporaneously at both sites (e.g. earthquake waves). This data selection approach is capable to replace a nonlinear time domain normalization, but no improvement of the waveform symmetry or the signal-to-noise ratio of the cross-correlation functions is observed in general.

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Offshore ambient-noise surface-wave tomography above 0.1 Hz and its applications

Cited by 36 publications

References 18 publications

Ambient seismic noise tomography at Ekofisk

Ambient seismic noise tomography at Ekofisk

2D time-lapse seismic tomography using an active time-constraint (ATC) approach

Performance of different processing schemes in seismic noise cross-correlations

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