Deep-water sea-floor array observations of seismo-acoustic noise in the eastern Pacific and comparison with wind and swell.
Natural Physical Sources of Underwater Sound. ( , Ed.).:165-174., Holland: Kluwer Academic Publishers 10.1007/978-94-011-1626-8_14 Abstract
We report results from the analysis of data from an array of Ocean-Bottom Seismographs (OBSs) employed in an array of 150 meter aperture at a depth of 3800 meters off the California coast. The array recorded noise samples four times per day for a month using pressure and three-component inertial sensors.
Comparison of the month-long noise spectrograms with swell spectrograms and wind hind-casts shows marked similarities. In the 0.05–1.0 Hz range the frequency-doubling of swell energy into sea-floor noise predicted by the wave interaction theory is evident. In the 1–10 Hz range the wind-related effects dominate. Lulls in the wind produce deep notches in the noise level. During times of high wind, saturation of the wind wave spectrum causes limiting and reduces the size of the noise maxima.
The wind estimates are from the meteorological model of the U.S. Navy Fleet Numerical Oceanography Center and the swell estimates are from their Global Spectral Ocean Wave Model.
Full Waveform Inversion of Seismic Interface Wave Data.
Full Field Inversion Methods in Ocean and Seismo-Acoustics. ( , Eds.)., Dordrecht: Klewer Academic Publishers Abstract
A technique for inverting marine seismic interface wave data for shear wave attenuation parameters of ocean sediments is presented. Because of the difficulty in estimating spectral ratios of seismograms in the case when multiple modes are present, a linear perturbation technique that uses the recorded time series seismogram or its envelope as input data is proposed. The technique is stable for tests using synthetic data. Application of the technique to data collected in the Gulf of Mexico yields a model producing a good fit to the data. However, a simple source model is insufficient to correctly predict modal excitations, and the source must be parameterized as part of the inversion process.
Implications of Deep-water Seismometer Array Measurements for Scholte Wave Propagation.
Shear Waves in Marine Sediments. ( , Eds.)., Dordrecht: Klewer Academic Publishers Abstract
A field exercise was conducted in March 1990 to make measurements of Scholte wave propagation characteristics in a deep ocean environment. Signals from a series of bottom explosive shots were recorded on an array of ocean bottom seismometers. Clear Scholte phases were observed on the vertical seismometers to ranges of 1.25 km, but were attenuated to noise levels by 2 km range. Collocated hydrophones did not detect the Scholte waves even at the closest ranges. The ratio of pressure (µPa) to vertical ground velocity (nm/s) was 68 dB in time windows dominated by body waves but only 20 dB in windows dominated by the Scholte wave. Group velocities were low (30-100 m/s) and showed considerable variability despite the expected uniformity of the seafloor in this abyssal environment.