High-quality seismic data recorded by a three-component, ocean borehole seismometer are used to determine the horizontal geophone azimuths to within ¿1.5¿. Analysis of water waves and first arrivals from 22 explosive charges fired to the downhole instrument show the effects of tilted sensors, shot mislocation, and dip of sediment-basement interface. Analysis also shows that the ocean subbottom seismometer (OSS IV) borehole package is not positioned below the sediment-basalt interface as previously believed but is actually locked in the sediments at some distance above the basement. The results of this study indicate that carefully located shots can be used to obtain geophone sensor azimuths to within ¿1.0¿, a precision adequate for most seismic and acoustic purposes. ¿American Geophysical Union 1987