Lamb waves observed during MASW surveys
article
Two fundamental modes of asymmetric and symmetric types of Lamb waves are observed from the near-surface seismic surveys by multichannel analysis of surface waves (MASW) method at two sites. One site consisted of loose soil charged with gas at shallow depth (at one and half meter). The other site was on top of hard, massive limestone possibly having a less stiff layer of shale or horizontal fracture at depth of approximately five meters. Lamb waves, originally misinterpreted as Rayleigh waves, were first identified from the prominent trend of both inverse (fundamental-mode asymmetric) and normal (fundamental-mode symmetric type) dispersion on the phase velocity image constructed from a multichannel analysis technique. Theoretical Lamb wave dispersion curves are then calculated and matched with the observed trend of dispersion on the image to calculate parameters such as thickness, and S- and P-wave velocities. These field examples indicate that Lamb waves can find useful applications in near-surface seismic surveying. Possible application may include detection of coal beds and plate voids as well as the cases illustrated here. © 2002 SEG Annual Meeting. All Rights Reserved.
Topics
TNO Identifier
953637
ISSN
10523812
Source
SEG Technical Program Expanded Abstracts, 21(1), pp. 1400-1403.
Publisher
Society of Exploration Geophysicists
Pages
1400-1403
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