Abstract

Sonobuoy arrays located over the Mid-Atlantic Ridge, during the French-American Mid-Ocean Undersea Study (FAMOUS), have been used to measure the spatial coherence of sound pressure radiated from sea quakes and provide refined estimates of epicenter locations. These measurements were made with array elements separated by two km and tracked to an accuracy of 30 m relative to a bottom-moored transponder. Spatial coherence, the normalized cross-spectral density, has been found to be as high as 0.7 at 13 Hz and to be typically about 0.5 between 16 and 60 Hz. Short-range events are significantly more coherent than long-range events whose onset is smeared in time. A maximum-likelihood array processor has been used to obtain accurate estimates of horizontal epicenter locations. The high-resolution processor yields about three times the resolving power of the conventional delay and sum processor. The resolving power obtained with these arrays is consistent with measured spatial coherence.

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