We began our expedition by heading full steam to the East Pacific Rise, a seafloor spreading center at the Cocos Ridge, where new oceanic crust of the Cocos plate is being formed. Here, we will begin collecting our geophysical data by deploying ocean-bottom seismometers (OBS).
Once we reached our study region, we activated the multibeam bathymetry equipment and sub-bottom profiler, and the splendid sounds of sonar pulses put a cheerful mood on everyone aboard the vessel. Together, these data produce a detailed map of the rugged seafloor marked by extinct volcanoes and deep scars. Since there are very few sediments blanketing the Cocos plate in this region, our maps expose this tectonic history of magmatism and formation of new oceanic crust at the mid-ocean ridge, and its ensuing deformation as it cools, cracks, twists, and bends during its journey towards the Mexico subduction zone.
The OBS program forms a major component of our scientific expedition, as these instruments will allow us to study the physical properties of the oceanic plate and determine how much it has cracked and become filled with seawater, which could lubricate its dive beneath the Mexico continental plate.
At its core, the OBS holds a seismometer to record acoustic signals and is protected inside a pressure vessel. A meticulous workflow is followed to assemble the instruments, program the seismometer, synchronize GPS and clock, and load them to the starboard deck of the Langseth. From there, we say “so long” for now, as each OBS is carefully tossed overboard, where a metal weight on the base of the instrument drags it several thousand meters down to the seafloor. Once in the deep dark abyss of the seafloor, the sensitive devices inside the OBSs record minuscule — but critical — motions of sediments on the seafloor and pressure changes in the water column due to sound waves generated by our ship, the Langseth.
After nearly a day of deploying instruments, our first profile is completely instrumented and the OBSs are happily recording, awaiting our seismic signals. Our first profile contains 26 OBS instruments spaced about 10 kilometers apart, extending from the Cocos mid-ocean ridge where the oceanic plate is born to around 300 kilometers away, where it has aged to approximately 5 million years old.
Next, we will prepare and deploy seismic sources so that we can start collecting data. All of the science team is itching in anticipation to see what we discover!
Brandon Shuck is a postdoctoral research fellow at Columbia Climate School’s Lamont-Doherty Earth Observatory.
