A comparison between a downhole seismometer and a seismometer on the ocean floor

Abstract We have compared the signal and noise characteristics recorded by a downhole seismometer and a nearby (within 200 m) ocean bottom seismometer in the deep ocean (5.5 km). Absolute noise levels and signal-to-noise ratios from the two instruments are remarkably similar. We attribute this unexpected similarity to the shallow emplacement depth of the downhole instrument (194 m subbottom) and the soft sediment into which it was clamped.