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

Allouche, Nihed; Drijkoningen, G.G.; Versteeg, W.; Ghose, Ranajit

doi:10.1190/1.3511524

Cited by 13 publications

(12 citation statements)

References 24 publications

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“…In the first part of the study, source and receivers were kept at a constant distance of 3 m from the sea floor, sufficient to generate and acquire Scholte waves as shown in Kruiver et al (2010) and El Allouche et al (2011). The acquisition parameters allowed to vary were nearest offset (x 1 ), receiver spacing (∆x), spread length (x) and variation of depth of streamer, related to depth of sea floor.…”

Section: Methodsmentioning

confidence: 99%

Optimizing Acquisition Parameters for MASW in Shallow Water

Diaferia¹,

Kruiver²,

Drijkoningen³

2013

London 2013, 75th Eage Conference en Exhibition Incorporating SPE Europec

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SUMMARYAnalogous to the use of Rayleigh waves in MASW on land, Scholte waves can be used to derive shear wave velocity profiles for the subsurface under water. These profiles are useful for dredging operations, offshore wind farms, oil rigs and pipelines. We have determined the optimal acquisition set up for the detection Scholte waves in shallow water. The nearest offset, receiver spacing and number of channels have been varied in a finite difference model consisting of a water layer on top of a sediment layer and a half space. The best configuration is a nearest offset of 10 m, receiver spacing of 1 m and 48 channels. When the seafloor is not horizontal, the source/receiver spread should follow the topography. When the distance between the source and the sea floor becomes too large, no Scholte waves are detected and subsequently no reliable Vs profile can be retrieved. In order to test the acquisition set up for a more realistic subsurface, a dipping layer and a filled channel structure were modeled. Whereas the inversion results for the dipping layer were satisfactory, the channel structure displayed large differences relative to the model, especially on the flanks.

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Section: Methodsmentioning

confidence: 99%

Optimizing Acquisition Parameters for MASW in Shallow Water

Diaferia¹,

Kruiver²,

Drijkoningen³

2013

London 2013, 75th Eage Conference en Exhibition Incorporating SPE Europec

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“…In Allouche et al (2011) this is worked out theoretically; as a rule of thumb it can be said that a source and/or receiver must be within some quarter of a wavelength to the interface such that the exponentially decaying (evanescent) part of the arrival makes the amplitude not too small.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…Examples of such waves have been reported in the past, like on land in global seismology (Daley & Hron, 1983) and in shallow land seismic (Roth & Holliger, 2000), called S* and a P S-wave respectively. Recently, such a non-geometric wave has also been discovered in a marine environment by Allouche et al (2011), where an evanescent P-wave in the water converts to a propagating S-wave in the water bottom. Its existence was shown by the use of OBC data and the modelling thereof.…”

Section: Introductionmentioning

confidence: 99%

Shear Waves in Streamer Data via Non-geometrical Conversions

Drijkoningen¹,

Allouche²

2012

Proceedings

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SUMMARYIn this paper we show that when an airgun source and a hydrophone streamer are situated in the vicinity of the water bottom, shear-related events are generated via the evanescent part of the P-wave in the water. The shear-related events are not only the often-used surface/Scholte waves but also body Swaves which can be reflected/refracted in the subsurface. The gain of this approach that neither source nor receiver is making any contact with the water bottom itself, making it possible to do shear-wave surveys on water in an efficient manner. We show that such shear-wave events are observed in real data, and can be reproduced by modelling. The results are further validated via real measurements in a borehole.

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“…Recently, Allouche et al (2010Allouche et al ( , 2011 have shown that these nongeometrically converted shear waves are clearly observable in data from a marine environment. They used data from water-bottom receivers in a shallow canal to demonstrate this statement, and they modeled seismic data to verify whether the observed response was consistent with the simulated response.…”

Section: Introductionmentioning

confidence: 99%

Nongeometrically converted shear waves in marine streamer data

et al. 2012

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Under certain circumstances, marine streamer data contain nongeometrical shear body wave arrivals that can be used for imaging. These shear waves are generated via an evanescent compressional wave in the water and convert to propagating shear waves at the water bottom. They are called "nongeometrical" because the evanescent part in the water does not satisfy Snell's law for real angles, but only for complex angles. The propagating shear waves then undergo reflection and refraction in the subsurface, and arrive at the receivers via an evanescent compressional wave. The required circumstances are that sources and receivers are near the water bottom, irrespective of the total water depth, and that the shear-wave velocity of the water bottom is smaller than the P-wave velocity in the water, most often the normal situation. This claim has been tested during a seismic experiment in the river Danube, south of Budapest, Hungary. To show that the shear-related arrivals are body rather than surface waves, a borehole was drilled and used for multicomponent recordings. The streamer data indeed show evidence of shear waves propagating as body waves, and the borehole data confirm that these arrivals are refracted shear waves. To illustrate the effect, finite-difference modeling has been performed and it confirmed the presence of such shear waves. The streamer data were subsequently processed to obtain a shear-wave refraction section; this was obtained by removing the Scholte wave arrival, separating the wavefield into different refracted arrivals, stacking and depth-converting each refracted arrival before adding the different depth sections together. The obtained section can be compared directly with the standard P-wave reflection section. The comparison shows that this approach can deliver refracted-shear-wave sections from streamer data in an efficient manner, because neither the source nor receivers need to be situated on the water bottom.

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

Cited by 13 publications

References 24 publications

Optimizing Acquisition Parameters for MASW in Shallow Water

Optimizing Acquisition Parameters for MASW in Shallow Water

Shear Waves in Streamer Data via Non-geometrical Conversions

Nongeometrically converted shear waves in marine streamer data

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