Acoustic clutter from buried submarine mud volcanoes

Submarine mud volcanoes occur in many parts of theworld's oceans and form an aperture for gas (mostly methane) and fluidized mud emission from the earth's interior. Their characteristics are of considerable interest to the geology, geophysics, geochemistry and underwater acoustics communities. The presence of mud volcanoes (and other related gassy sediment structures) has a profound effect on low frequency acoustic reverberation. Reverberation data from the Strait of Sicily indicate high scattering from buried mud volcanoes from 150-800 Hz at ranges of 10 km. The scattering decreases sharply above 800 Hz. Two hypotheses are explored regarding the scattering mechanism, scattering by sediment entrained gas, and scattering from the mud volcano structure itself. Modeling indicates that large bubble sizes (mean radius greater than 1 cm) are required to fit the scattering data, suggesting that this hypothesis may be unreasonable. The scattering from the structure itself appears to be the most reasonable scattering mechanism. The cause of the observed sharp decrease with frequency above 800 Hz in the backscattered response is not presently understood.