Abstract

Multiple geophysical datasets were recorded during the international cooperative pilot experiment, Monterey Bay Ocean Bottom International Seismic Experiment (MOISE). This experiment, conducted from June to September 1997, demonstrated the feasibility of installing, operating, and recovering different geophysical sensors (seismometers, electromagnetometers and environmental sensors).

The seismic noise level was stable throughout the experiment. The noise level was comparable to a high noise model for periods below 15 sec and showed strong diurnal variations at longer periods. We demonstrate that these diurnal variations can be removed from the vertical component by subtracting the effect of the horizontal components, decreasing the vertical noise level by up to 40 db. We investigate possible coherence between long-period seismic, electromagnetic, and environmental data. The coherence between the vertical seismic signal and pressure and current speed is close to unity between 2 × 10-5 and 10-4 Hz. In particular, there is a peak of coherence at 2.3 × 10-5 Hz (12 hr), which is a consequence of tidal effects. No significant high coherence is observed with the vertical magnetic field.

The MOISE experiment demonstrates that permanent broadband seismic and geophysical observatories can now be installed on the seafloor. It also illustrates the importance of installing various kinds of geophysical sensors in order to increase the signal-to-noise ratio of seismic data, validating the concept of multiparameter ocean-bottom stations.

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