1 Revista Brasileira de Geofísica 2009 Vol: 27(2):. DOI: 10.1590/S0102-261X2009000200004

Propriedades acústicas (velocidade de propagação e coeficiente de atenuação) de sedimentos marinhos coletados nas proximidades da Ilha do Cabo Frio, RJ

Acoustic properties (wave propagation velocity and attenuation coefficient) of marine sediments are related to grain-size. In laboratory, an ultrasonic system of 2.25 MHz was implemented to take measures of compressional wave propagation. Nine (9) piston-cores were collected, totaling twelve (12) meters of sediment. Before splitting the cores, approximately 2,550 measurements were taken. Results permitted to construct sound speed profiles and 3D attenuation coefficient diagram in the frequency domain. Interfaces between sedimentary layers were also identified. The highest value of sound speed (1,752 m/s) was measured in medium sands. Sandy mud and consolidated mud registered the lowest values of this research (1,492 and 1,498 m/s, respectively), indicating a trend of increased Vp related to increased grain-size. The highest values of attenuation coefficient (1,750 and 1,550 dB/m, respectively) were measured in muddy sands and sandy mud, for the reference frequency 1.6 MHz. The lowest values were registered by fine sands and fluid mud (400 and 500 dB/m). These results indicate that cohesive sedimentscomposed by heterogeneous mixtures have higher values of attenuation.

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