Removal of water‐layer multiples from multicomponent sea‐bottom data

Osen, A.; Amundsen, Lasse; Reitan, Arne; Helgesen, Hans Kristian

doi:10.1190/1.1826410

Cited by 18 publications

(16 citation statements)

References 3 publications

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“…Besides a small influence of the water depth on the appearance of the v s,app profiles, we find that the removal of water multiples might be useful for water depth shallower than ∼1 km ( Fig. 6; Osen et al 1999;Thorwart & Dahm 2005) in order to prevent a distortion of the obtained results. We find from our synthetic test that the uppermost mantle shear wave velocity can be identified.…”

Section: O N C L U S I O N a N D O U T L O O Kmentioning

confidence: 90%

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Oceanic lithosphericS-wave velocities from the analysis ofP-wave polarization at the ocean floor

Hannemann¹,

Dahm

Lange³

2016

Geophys. J. Int.

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S U M M A R YOur knowledge of the absolute S-wave velocities of the oceanic lithosphere is mainly based on global surface wave tomography, local active seismic or compliance measurements using oceanic infragravity waves. The results of tomography give a rather smooth picture of the actual S-wave velocity structure and local measurements have limitations regarding the range of elastic parameters or the geometry of the measurement. Here, we use the P-wave polarization (apparent P-wave incidence angle) of teleseismic events to investigate the S-wave velocity structure of the oceanic crust and the upper tens of kilometres of the mantle beneath single stations. In this study, we present an up to our knowledge new relation of the apparent Pwave incidence angle at the ocean bottom dependent on the half-space S-wave velocity. We analyse the angle in different period ranges at ocean bottom stations (OBSs) to derive apparent S-wave velocity profiles. These profiles are dependent on the S-wave velocity as well as on the thickness of the layers in the subsurface. Consequently, their interpretation results in a set of equally valid models. We analyse the apparent P-wave incidence angles of an OBS data set which was collected in the Eastern Mid Atlantic. We are able to determine reasonable S-wave-velocity-depth models by a three-step quantitative modelling after a manual data quality control, although layer resonance sometimes influences the estimated apparent S-wave velocities. The apparent S-wave velocity profiles are well explained by an oceanic PREM model in which the upper part is replaced by four layers consisting of a water column, a sediment, a crust and a layer representing the uppermost mantle. The obtained sediment has a thickness between 0.3 and 0.9 km with S-wave velocities between 0.7 and 1.4 km s −1 . The estimated total crustal thickness varies between 4 and 10 km with S-wave velocities between 3.5 and 4.3 km s −1 . We find a slight increase of the total crustal thickness from ∼5 to ∼8 km towards the South in the direction of a major plate boundary, the Gloria Fault. The observed crustal thickening can be related with the known dominant compression in the vicinity of the fault. Furthermore, the resulting mantle S-wave velocities decrease from values around 5.5 to 4.5 km s −1 towards the fault. This decrease is probably caused by serpentinization and indicates that the oceanic transform fault affects a broad region in the uppermost mantle. Conclusively, the presented method is useful for the estimation of the local S-wave velocity structure beneath ocean bottom seismic stations. It is easy to implement and consists of two main steps: (1) measurement of apparent P-wave incidence angles in different period ranges for real and synthetic data, and (2) comparison of the determined apparent S-wave velocities for real and synthetic data to estimate S-wave velocity-depth models.Key words: Time-series analysis; Body waves; Theoretical seismology; Oceanic transform and fracture zone processes. I N T RO D U C T I O NThe p...

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Section: O N C L U S I O N a N D O U T L O O Kmentioning

confidence: 90%

“…Nevertheless, the water depth has only a minor influence on the appearance of the v s,app profiles at least for the deep ocean, but a removal of the water multiples (Osen et al 1999;Thorwart & Dahm 2005) before deconvolution might be useful for shallow water depths to prevent influences by wave form distortions.…”

Section: Influence Of Water Depthmentioning

confidence: 99%

Oceanic lithosphericS-wave velocities from the analysis ofP-wave polarization at the ocean floor

Hannemann¹,

Dahm

Lange³

2016

Geophys. J. Int.

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“…The P-and S-wave velocities are also required when decomposing the wavefield in up-and down-going waves. Wave-field decomposition techniques have been successful to suppress water layer multiples in active seismic (e.g., Amundsen and Reitan 1995;Osen et al 1999) or passive seismology studies (e.g., Thorwart and Dahm 2005). The shear strength of the mushy layer is quite small.…”

Section: Introductionmentioning

confidence: 99%

Inversion of Scholte wave dispersion and waveform modeling for shallow structure of the Ninetyeast Ridge

2008

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The construction of S-wave velocity models of marine sediments down to hundreds of meters below the seafloor is important in a number of disciplines. One of the most significant trends in marine geophysics is to use interface waves to estimate shallow shear velocities which play an important role in determining the shallow crustal structure. In marine settings, the waves trapped near the fluid-solid interface are called Scholte waves, and this is the subject of the study. In 1998, there were experiments on the Ninetyeast Ridge (Central Indian Ocean) to study the shallow seismic structure at the drilled site. The data were acquired by both ocean bottom seismometer and ocean bottom hydrophone. A new type of seafloor implosion sources has been used in this experiment, which successfully excited fast and high frequency (>500 Hz) body waves and slow, intermediate frequency (<20 Hz) Scholte waves. The fundamental and first higher mode Scholte waves have both been excited by the implosion source. Here, the Scholte waves are investigated with a full waveform modeling and a group velocity inversion approach. Shear wave velocities for the uppermost layers of the region are inferred and results from the different methods are compared. We find that the full waveform modeling is important to understand the intrinsic attenuation of the Scholte waves between 1 and 20 Hz. The modeling shows that the S-wave velocity varies from 195 to 350 m/s in the first 16 m of the uppermost layer. Depths levels of high S-wave impedance contrasts compare well to the layer depth derived from a P-wave analysis as well as from drilling data. As expected, the P-to S-wave velocity ratio is very high in the uppermost 16 m of the seafloor and the Poisson ratio is nearly 0.5. Depth levels of high S-wave impedance contrasts are comparable to the layer depth derived from drilling data.

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“…The amplitudes of the propagator coefficients [equations (2) through (5)] are wavefield decomposition filters (Osen et al, 1999). Before extrapolating the recorded wavefield to depth ∆z, the wavefield is decomposed into up-and downgoing P-and S-waves.…”

Section: Methodsmentioning

confidence: 99%

Propagator inversion for shallow structure

Vossen¹,

Trampert²,

Curtis³

2003

SEG Technical Program Expanded Abstracts 2003

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SummaryNear-receiver material properties are required to separate the recorded wavefield into P-and S-, and up-and downgoing components, and can enhance static corrections and improve depth estimates of refractors. We present an approach for estimating local material properties between two geophones, one buried and one positioned at the surface. We do so by inverting the vertical wavefield propagator in the time domain. Both its amplitude and phase are used to determine the local structure between the two geophones. Synthetic experiments and noise tests demonstrate that the propagator inversion provides accurate estimates for P and S velocities, and is robust with respect to near-surface reverberations.

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Removal of water‐layer multiples from multicomponent sea‐bottom data

Cited by 18 publications

References 3 publications

Oceanic lithosphericS-wave velocities from the analysis ofP-wave polarization at the ocean floor

Oceanic lithosphericS-wave velocities from the analysis ofP-wave polarization at the ocean floor

Inversion of Scholte wave dispersion and waveform modeling for shallow structure of the Ninetyeast Ridge

Propagator inversion for shallow structure

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