Installing the Borehole Seismic System
Procedure for installing the borehole seismic system in an existing borehole from a conventional, nondrilling, research vessel. The ship is maintained within a 10-meter watch circle by dynamic positioning and the Global Positioning System navigation. Acoustic transponders on the seafloor assist in locating the lead-in package relative to the re-entry cone. A camera and lights on the lead-in package at the bottom of the borehole seismometer also assist in locating the cone. Once re-entry is completed the system is lowered until the seafloor data recording package lands in the cone. The control vehicle has propulsion and additional navigational aids to manipulate the string near the seafloor. Once the system has been tested in place, the tether at the top of the recording package is released and the control vehicle returns to the surface. Recovery of the recording package is carried out with a grappling hook attached to the bottom of the control vehicle. At OSN-1 the water depth is 4,407 meters, the re-entry cone is 5 meters across, and the borehole seismometer was emplaced 248 meters below the seafloor. (Illustration by Jayne Doucette)
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