No abstract

We use data from the 1983 Ngendei Seismic Experiment in the southwest Pacific to compare vertical component seismograms recorded by a borehole seismometer with those from ocean bottom seismometers. The borehole seismometer, the Marine Seismic System (MSS), was emplaced 54 m into the oceanic crust at the Ngendei site. Ocean bottom seismometers (OBSs) from the Scripps Institution of Oceanography were located atop 70 m of sediment and all were within 0.5 km of the borehole. Numerous seismic refraction shots were recorded simultaneously by both the borehole and ocean bottom instruments, as well as a small number of regional earthquakes. The waveforms and instrument-corrected spectra for compressional waves from these events are nearly identical for the two different instruments, while the absolute amplitudes of the arrivals differ by no more than 4 dB. Since borehole noise levels are 10 to 15 dB lower than the seafloor levels, there is a general increase in the signal-to-noise ratio for the buried instrument. The similarity in absolute amplitudes for these observations agrees with results obtained from simple synthetic seismogram calculations.

No abstract