SHEAR SPEED GRADIENTS AND RESONANCES IN OCEAN SEISMO-ACOUSTIC MODELLING

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Authors
  1. Chapman, D.M.F.
Corporate Authors
Defence Research Establishment Atlantic, Dartmouth NS (CAN)
Abstract
Measurements of infrasonic seismo-acoustic ambient noise with an ocean bottom seismometer (OBS) in shallow water have uncovered an unusual phenomenon: the noise spectrum of the horizontal component of seabed velocity shows several prominent evenly-spaced peaks in the frequency range 0-8 Hz, whereas the noise spectra of both the acoustic pressure and the vertical component of seafloor velocity show very weak - or nonexistent-features at the same frequencies. Using an elastic multi-layer plane-wave propagation model implemented in Mathematica (TRADEMARK), these features are attributed to shear-wave resonances in the upper sediment, which consists of layers of clay and silt of low shear speed (7-150 m/s) overlying a much faster glacial till layer. Not surprisingly, the frequency spacing infinite difference f of successive resonances appears to be governed by the two-way travel time through the sediment; however, the frequency of the fundamental resonance is highly dependent upon the profile of shear speed versus depth. TRUNCATED
Keywords
Sound speed profiles;Seismo-Acoustic modelling;Geophones
Date of publication
01 Jul 1996
Number of Pages
12
DSTKIM No
97-03766
CANDIS No
503806
Format(s):
Hardcopy;Document Image stored on Optical Disk

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