Constraints on the shallow seismic structure at Ocean Drilling Program Site 1107, Ninetyeast Ridge, from implosive bottom sources and airgun shots

Grevemeyer, Ingo; Flueh, Ernst R.; Herber, Rolf; Villinger, Heinrich

doi:10.1029/1999gl900151

Cited by 6 publications

(13 citation statements)

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“…The body wave analysis of Grevemeyer et al (1999) showed a good agreement between the P-wave seismic structure and the results obtained by drilling. The shear wave seismic structure has not been analyzed with the data so far and is studied in this paper.…”

Section: Introductionmentioning

confidence: 76%

“…The soft mushy layer is mostly controlling the propagation and dispersion of the Scholte waves between 5 and 10 Hz. How does our S-wave velocity model compare to measurements from ODP site 757 and P-wave study of Grevemeyer et al (1999)? Borehole measurements of the P-wave velocity, density, vaneshear strength, and lithology have been described to a depth of 500 m in Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Density obtained from ODP report, Peirce et al (1989a). e P-wave velocity model collected from P-wave study of Grevemeyer et al (1999). f The image of Vs at 500 m bsf, obtained from smallest misfit model of the group velocity inversion ratio is about 0.49 in the mushy layer.…”

Section: Discussionmentioning

confidence: 99%

“…Firstly, we aim to derive a simple model with two layers only; the S-wave velocities and interface depths are allowed to vary over a large range during inversion. Information on the P-wave velocities were taken from the experiment report, a P-wave refraction seismic study of Grevemeyer et al (1999), and Peirce et al (1989a). We apply a direct search algorithm to invert simultaneously group velocities of the fundamental and first higher mode as well as the short branch of phase velocities.…”

Section: Inversion For Shear Wave Velocitymentioning

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: Introductionmentioning

confidence: 76%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Inversion For Shear Wave Velocitymentioning

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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“…A 3‐D seismic survey using ocean bottom hydrophones (OBHs) around ODP site 757 was designed to reveal the small‐scale structure of the Ninetyeast Ridge volcanic edifice. The survey complements a 550 km long seismic refraction profile investigating the architecture of the crust and upper mantle (Grevemeyer et al 2001) and high‐resolution seismic and multibeam sonar studies of the immediate vicinity of the NERO site (Grevemeyer et al 1999; Kopf et al 2001). A heterogeneous upper crustal architecture, comprising an extrusive layer formed at discrete volcanic centres at sea level (Peirce et al 1989), is expected and can only be captured insufficiently by a 2‐D study along selected but not representative profiles.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional seismic refraction tomography of the crustal structure at the ION site on the Ninetyeast Ridge, Indian Ocean

Schlindwein¹,

Bönnemann²,

Reichert³

et al. 2003

Geophysical Journal International

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SUMMARY We have performed a 3‐D seismic refraction tomography of a 48 × 48 km2 area surrounding ODP site 757, which is planned to host an International Ocean Network (ION) permanent seismological observatory, called the Ninetyeast Ridge Observatory (NERO). The study area is located in the southern part of the Ninetyeast Ridge, the trail left by the Kerguelen hotspot on the Indian plate. The GEOMAR Research Centre for Marine Geosciences and the Federal Institute for Geosciences and Natural Resources acquired 18 wide‐angle profiles recorded by 23 ocean bottom hydrophones during cruise SO131 of R/V Sonne in spring 1998. We apply a first arrival traveltime tomography technique using regularized inversion to recover the 3‐D velocity structure relative to a 1‐D background model that was constructed from a priori information and averaged traveltime data. The final velocity model revealed the crustal structure down to approximately 8 km depth. Resolution tests showed that structures with approximately 6 km horizontal extent can reliably be resolved down to that depth. The survey imaged the extrusive layer of the upper crust of the Ninetyeast Ridge, which varies in thickness between 3 and 4 km. A high‐velocity anomaly coinciding with a positive magnetic anomaly represents a volcanic centre from which crust in this area is thought to have formed. A pronounced low‐velocity anomaly is located underneath a thick sedimentary cover in a bathymetric depression. However, poor ray coverage of the uppermost kilometre of the crust in this area resulted in smearing of the shallow structure to a larger depth. Tests explicitly including the shallow low‐velocity layer confirmed the existence of the deeper structure. The heterogeneity of the upper crust as observed by our study will have consequences for the waveforms of earthquake signals to be recorded by the future seismic observatory.

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Interplay between magmatic accretion, spreading asymmetry and detachment faulting at a segment end: Crustal structure south of the Ascension Fracture Zone

Bialas

Dannowski

Reston

2015

Earth and Planetary Science Letters

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Constraints on the shallow seismic structure at Ocean Drilling Program Site 1107, Ninetyeast Ridge, from implosive bottom sources and airgun shots

Cited by 6 publications

References 14 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

Three-dimensional seismic refraction tomography of the crustal structure at the ION site on the Ninetyeast Ridge, Indian Ocean

Interplay between magmatic accretion, spreading asymmetry and detachment faulting at a segment end: Crustal structure south of the Ascension Fracture Zone

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