Text and photo: Andreia Plaza-Faverola, researcher CAGE; project leader SEAMSTRESS.
By the time the last Ocean Bottom Seismometer (OBS) was diving deep into the ocean, big waves and strong winds reached us. We spent a day or so surviving that feeling of seasickness that accompanies you for a while even when you get back ashore.
Our next objective was to investigate how the geology underlying the OBSs. For this the University vessel ( RV Helmer Hanssen) is equipped with several instruments that produce and record acoustic waves of various frequencies. The lower the frequency of the wave, the deeper we manage to penetrate the ground to gain a picture of the underlying structures. But the higher the frequency, the more detail we get. We used every instrument available to get a highly detailed 3D image of the underground.
We collected geophysical data along 12 profiles and with the software onboard immediately produced spectacular “radiographies” of the Mother Earth’s submerged mountains and cracks beneath the seafloor in this remote part of the globe.
We started with 2D surveys (the ship moves in a straight line). Everything went so smooth and the excitement about amazing data was such, that we decided to do a 3D survey (the ship moves in parallel and closely spaced lines and the recorded data is then interpolated to get a volume).
To image deeper we use an air source that produces an acoustic signal with 20-500 Hz. For 2D lines, we connect the cables one after the other one (we refer to it as the green spaghetti).
To image in 3D we put the cables one next to the other. Changing from one configuration to the other one implies a lot of action on deck for the crew, our engineers, ourselves and even our colleagues form AWI helped on deck pulling and connecting hydrophones for the surveys. Also, the processing team had a lot of action and a sufficient amount of data to keep us awake during the night shifts.
It was a productive research cruise with a great crew and lots of inspiring moments. We had intense research discussions and collected significant data sets for the Seamstress project. Part of the new lines complement a data set we are using for a scientific drilling proposal (IODP).
We sail satisfied to our next target before heading to our final destination: Home!