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Nongeometrically converted shear waves in marine streamer data

Guy Drijkoningen, Nihed El Allouche, Jan Thorbecke and Gabor Bada
Nongeometrically converted shear waves in marine streamer data
Geophysics (November 2012) 77 (6): P45-P56

Abstract

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.


ISSN: 0016-8033
EISSN: 1942-2156
Coden: GPYSA7
Serial Title: Geophysics
Serial Volume: 77
Serial Issue: 6
Title: Nongeometrically converted shear waves in marine streamer data
Affiliation: Delft University of Technology, Department of Geoscience and Engineering, Delft, Netherlands
Pages: P45-P56
Published: 20121101
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 16
Accession Number: 2013-010829
Categories: Applied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
N47°19'60" - N47°45'00", E18°45'00" - E19°30'00"
N43°36'00" - N49°01'00", E08°13'60" - E29°40'00"
Secondary Affiliation: TXM Oil and Gas Exploration, HUN, Hungary
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 201308
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