NZ3D Blog #4: All aboard

With all the land seismometers and OBS instruments now in place and waiting patiently for the data to roll in, it’s time for the marine part of our experiment to begin! The vessel we are using is the R/V Marcus G Langseth, a research vessel from Lamont-Doherty Earth Observatory in New York. The science party joined the main ship’s crew in Tauranga and the salty sea life began! The science party on board is a bit different to the land deployment crew. On the Langseth there are a mix PhD students, early career scientists, and more senior staff from the UK, USA, New Zealand and Japan.

First things first, we had a safety drill. We all had to go to our muster stations when the alarm rang and grab a life vest and immersion suit. Everyone then gathered on the bridge and the captain briefed us on what to do in an emergency and we got a demonstration of how to put the immersion suits on. Next was time for us to try and put them on ourselves. All the crew can go from human to lobster in under 60 seconds which, trust me, is no easy feat!!

The R/V Marcus G Langseth is a brilliant research vessel, equipped with all we need to start acquiring our data. The crew are super friendly and enjoy getting the science party up on the decks to help deploy all the kit. The ship will be towing 4 streamers, each 6km long, as well as the acoustic source generators. That’s a lot of kit to be towing!

We started early one morning putting out the streamers one by one to test they were in ship-shape (haha) condition and that all the birds were working and in the right place. Birds are plastic tools that get their names from small wings that protrude either side. These are no ordinary pigeons though! The birds can communicate with each other and the main lab, and the wings can be moved to keep the streamers as straight as possible, stop them from tangling up with each other, and make sure they stay at the right depths. We want our streamers to be 8m below the sea surface.

Once we are sure everything is in working order, everything gets pulled back in ready for the real deal. The whole testing process takes about 3 days. Next we headed over to the survey area. This is 17km offshore from the area around Gisborne (where we were deploying the land instruments) at its closest, and 77km at it’s furthest. Once there, we put all 4 streamers out, using 2 paravanes. Paravanes are large buoys which help keep the streamers spread out and away from each other. Getting the streamers tangled up would be terrible! The acoustic source generators are next. These will be operating in flip-flop. No not the shoe, this means one releases an acoustic wave, and then the other, then back to the first, then… you get the idea. The acoustic waves generated here will travel down through the rocks in the subsurface, and get recorded by the streamers, the OBS instruments lying on the seafloor, and of course, our land seismometers. Pretty clever right?!

Once we’ve finished, we will be able to pick up all our instruments, download all the data, and use it to make a beautiful 3D map of the subsurface of the Hikurangi margin. But that’s a long way off. We’ve only just started recording data and will be out here for 5 weeks in total. But so far so good!! Everything seems to be going to plan and the data we can see from the streamers is looking pretty nice.

For more information about the voyage you can read: Hikurangi Seismic Surveying Fact Sheet

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