Robert D. Stoll
Edgar Bautista
Lamont--Doherty Geol. Observatory of Columbia Univ., Palisades, NY 10964
A new source is described for generating SH and Love waves in marine sediments immediately beneath the seafloor. The source, which generates torsional pulses over a small circular area of the seabottom by utilizing the energy stored in a rotating flywheel, and an array of geophones are both deployed on the seafloor. In theory, in a laterally homogeneous medium, this type of source should produce a radially symmetric wave field composed only of horizontally polarized shear waves (SH waves) and the resulting Love modes caused by vertical inhomogeneity. However, in reality, some of the energy may be converted to p-wave and SV-wave motion for a variety of different reasons (e.g., imperfect coupling with the seafloor, anisotropy and lateral inhomogeneity). Since most marine sediments exhibit a strong gradient in shear-wave velocity near the seafloor, it is possible to use the dispersion of the resulting Love waves as a basis for inversion to obtain a geoacoustic model of the bottom. Data from shallow water experiments in New York harbor are presented and a sediment model derived by constrained, least-squares inversion is described. Some results from experiments on land are also presented and the potential for use on the ice sheet is discussed. [Work supported by ONR, Code 11250A.]