Ocean Bottom Seismometer Overboard

The first week of the Hawaiian-Emperor Seamount Seismic Experiment has been filled with tossing things over the side of the ship – not throwing just anything overboard, but specifically deploying Ocean Bottom Seismometers (OBS) at regular intervals along transects of ocean floor specifically selected to help answer our science queries. While the crew of the R/V Langseth deftly avoided hurricane Olivia, the OBS technicians and the science party for our expedition have been working around the clock to achieve the first phase of our expedition goals – drop 70 OBSs to the seafloor, where they act as recording devices for the seismic waves that allow us to map the oceanic plate and upper mantle beneath Hawaii.
OBS deployment

OBSs are aptly named instruments – they consist primarily of a seismometer (just like the ones that record earthquakes all over the globe), a data logger with battery pack (to record what the seismometer picks up), an anchor (to keep the instrument on the seafloor), and flotation devices (to bring the instrument back to the surface when the experiment is done). In other words, a seismometer modified to work at the ocean bottom.

It is important that every one of these instruments is in the best working condition. The graduate students on board our expedition have been helping the OBS technicians with final assembly and checks on each instrument prior to deployment. The technicians make sure that the data logger is operational, that the instrument will respond to acoustic commands (acoustic commands are how we tell the instrument when to drop anchor and come back to the surface), and that the batteries are fully charge. At the same time, students help to attach additional flotation, tighten any loose screws, and ensure that the locator beacons are securely attached. Once the instrument has passed all tests and is deemed ready for deployment, it is lifted by crane over the side of the ship and dropped to the depths.

So far we have successfully deployed 53 OBSs, and the team is operating like a well-oiled machine. In only a few days we should have all of our instruments on the seafloor and be ready to move on to the next phase of the expedition!

Bridgit Boulahanis, Lamont-Doherty Earth Observatory

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