Research Begins: Throwing Instruments into the Abyss
We started our expedition at full speed to the East Pacific Rise, a seafloor spreading center on the Cocos Ridge where the new oceanic crust of the Cocos Plate is forming. Here, we’ll begin collecting our geophysical data by deploying an ocean floor seismometer (OBS).
Once we reached our study area, we activated the multibeam bathymetry equipment and seafloor profiler, and the beautiful sound of the sonar ping put everyone on board in a good mood. Together, the data produced a detailed map of the rugged seafloor marked by extinct volcanoes and deep scars. Because very little sediments cover the Cocos Plate in the region, our map reveals the tectonic history of magmatism and the formation of the new oceanic crust of the mid-ocean ridge, along with the consequent cooling, cracking, twisting and bending of it. deformed. Its journey to the subduction zone of Mexico.
Multibeam bathymetric mosaic of seafloor topography in the Orozco fault zone. The colors represent the depth of the ocean floor (warm=shallow, cool=deep) in an area of ocean below our ship’s track. The lines represent the faulted oceanic crust, which changes direction as the oceanic plate deforms due to tectonic stress.Image: Brian Boston
The OBS program is a major component of our scientific expeditions, as these instruments will allow us to study the physics of the oceanic plate and determine the extent to which it has broken up and filled with seawater, which may lubricate its diving under the Mexican continental plate.
At the heart of the OBS is a seismometer to record acoustic signals and is protected within a pressure vessel. Follow a meticulous workflow to assemble instruments, program seismometers, synchronize GPS and clocks, and load them onto Langseth’s starboard deck. From there, we now say “so long” as each OBS is carefully tossed into the sea, dragged by the metal weights on the base of the instrument to the ocean floor several kilometers down the road. Once in the deep, dark abyss of the ocean floor, sensitive equipment within the OBS records the tiny but vital movements of seafloor sediments, as well as changes in water column pressure due to the sound waves produced by our boats, Launces.
Prepare the seafloor seismometer instrument prior to deployment. Top left: Unassembled seafloor seismometer. Bottom left: Brian Boston (LDEO), Jorge Real-Pérez (UNAM) and Langseth Science Technician Cody Bahlau preparing the instrument. Right: A fully assembled seafloor seismometer awaiting deployment.Photo: Brandon Shook
The science team and Langseth staff moments before deploying the instrument. The team securely attached the instrument to an A-frame, which used hydraulics to lift the instrument to the side of the boat, then released it to begin its descent to the seafloor.Photo: Brandon Shook
After nearly a day of instrument deployment, our first profile is fully instrumented and OBS is happily recording, awaiting our seismic signal. Our first profile contains 26 OBS instruments about 10 kilometers apart, extending about 300 kilometers from the Cocos mid-ocean ridge, where the oceanic plate was born, and it has aged to about 5 million years.
Next, we will prepare and deploy the seismic source so we can start collecting data. All scientific teams are eager to see our findings!
Panorama of Langseth. Subsea seismograph operations are carried out on the main deck on the starboard side of the vessel. The multi-channel hydrosphere streamer is shown on the right, which we will use in the second half of the experiment to collect different types of data along the same profile.Photo: Brandon Shook
Brandon Shuck is a postdoctoral researcher at the Lamont-Doherty Earth Observatory at the Columbia Climate Institute.
