Estimating shallow shear velocities with marine multicomponent seismic data

Ritzwoller, M. H.; Levshin, A. L.

doi:10.1190/1.1527099

Cited by 61 publications

(52 citation statements)

References 51 publications

(34 reference statements)

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“…Nolet and Dorman (1996) used waveform fitting to show that starting from 30 m/s, S-wave velocity increases with a gradient of 2.8 m/s per meter over the first 150 m of sediment. Ritzwoller and Levshin (2002) constructed a reliable S-wave model to a depth of 200 m. In other studies, Forbriger (2003a, b) observed a remarkably good resolution of S-wave velocity in 6 and 16 m down to the bedrock, respectively. With their promising approach, Bohlen et al (2004) are able to apply to a dense net of profiles to derive 2-D models of surface S-wave velocity.…”

Section: Discussionmentioning

confidence: 99%

“…Nolet and Dorman (1996) adapted method of non-linear waveform fitting to accommodate multidimensional model and applied it to invert several record sections of Scholte waves. Ritzwoller and Levshin (2002) presented multiwave inversion method which can adapt to a wide variety of information in marine seismic data. Forbriger (2003a, b) described his new approach on the inversion of shallow-seismic wavefields.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

2008

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“…up to 300 m in Ritzwoller & Levshin (2002) and for the upper tens of metres in Nguyen et al (2009)). The success of these techniques is directly related to the distance of the active source to the seafloor.…”

Section: Previous Studies Of Oceanic S-wave Velocitymentioning

confidence: 99%

“…The success of these techniques is directly related to the distance of the active source to the seafloor. The closer the source is located to the seafloor the more acoustic energy can be converted into S-wave energy (Ritzwoller & Levshin 2002). The inversion of these active data results in high resolution S-wave velocity models, but it is limited to the upper hundreds of metres beneath the seafloor.…”

Section: Previous Studies Of Oceanic S-wave Velocitymentioning

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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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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“…Another popular approach is to invert the dispersion curves of the Scholte wave ͑e.g., Caiti et al, 1994;Ritzwoller and Levshin, 2002;Park et al, 2005͒. These P-SV polarized waves, traveling along the water-bottom interface, are highly sensitive to the shear-wave velocity.…”

Section: Introductionmentioning

confidence: 99%

Converted waves in a shallow marine environment: Experimental and modeling studies

et al. 2011

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Seismic waves converted from compressional to shear mode in the shallow subsurface can be useful not only for obtaining shear-wave velocity information but also for improved processing of deeper reflection data. These waves generated at deep seas have been used successfully in hydrocarbon exploration; however, acquisition of good-quality converted-wave data in shallow marine environments remains challenging. We have looked into this problem through field experiments and synthetic modeling. A high-resolution seismic survey was conducted in a shallowwater canal using different types of seismic sources; data were recorded with a four-component water-bottom cable. Observed events in the field data were validated through modeling studies. Compressional waves converted to shear waves at the water bottom and at shallow reflectors were identified. The shear waves showed distinct linear polarization in the horizontal plane and low velocities in the marine sediments. Modeling results indicated the presence of a nongeometric shear-wave arrival excited only when the dominant wavelength exceeded the height of the source with respect to the water/sediment interface, as observed in air-gun data. This type of shear wave has a traveltime that corresponds to the raypath originating not at the source but at the interface directly below the source. Thus, these shear waves, excited by the source/water-bottom coupled system, kinematically behave as if they were generated by an S-wave source placed at the water bottom. In a shallow-water environment, the condition appears to be favorable for exciting such shear waves with nongeometric arrivals. These waves can provide useful information of shear-wave velocity in the sediments.

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Estimating shallow shear velocities with marine multicomponent seismic data

Cited by 61 publications

References 51 publications

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

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

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

Converted waves in a shallow marine environment: Experimental and modeling studies

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