After 32 days at sea on board the R/V Marcus G. Langseth, data acquisition is finally complete. It’s been quite an adventure. Data collection went smoothly, with only a few tense moments of bad weather and instrument down-time. The data looks great and now the only thing standing between the crew and land is the task of pulling in all the gear.
Everyone gets involved helping to make sure we get everything back on board safely and quickly. After bringing the acoustic sources on board, we begin to slowly reel in the streamers, removing the birds one by one.
Once all the birds are on board and the streamers are on their reels, we need to bring in the tailbuoy and paravanes. These are huge pieces of equipment and require big winches to secure them on deck.
We have collected some really high quality data on board, with the streamer dataset already looking really detailed. The final steps will be to pick up the ocean bottom seismometers and land instruments, and see the data they have been recording this last month.
A huge thank you to all the Langseth crew, science party and land deployment team, it’s been great!
There are 3 places on board where we can steer the ship. First and foremost is the bridge. This is where either the Captain or one of the mates can be found and usually who has control.
The second place we can steer from is the Main Lab. This is where the science party can be found on shift, doing data quality control, taking logs and monitoring all the equipment. We often steer from here while collecting data to keep our streamers recording at full coverage. There are A LOT of screens in here!
The final place we can steer to boat from is the engine room. This area is usually off-limits for the science party, but today we were lucky enough to be taken on an engine room tour.
The chief engineer Matt took us into ‘the belly of the beast’, as he called it, where all the machinery that keeps the boat up and running can be found. After a brief chat in the control room, we put on our ear protectors and went exploring.
The engines themselves are pretty huge, and are used to power 2 rotating shafts which drive the boat. Matt took the cover off so we could see all the pistons moving as the engine chugged away. The shafts are attached to propeller blades which can be moved outwards, perpendicular to the rotation, to control the ship’s speed. The speed of the ship depends on the angle of the propellers. The engine produces a huge amount of heat, but this is not wasted and is used to create fresh water for us while on board. Fresh water can be made in 2 ways on here, by an evaporator which harnesses heat produced by the engine, and we top this up by reverse osmosis of sea water.
There are 2 other, smaller engines that are used to power the compressor. This is a five-stage process which compresses air to 2000psi for use in our data acquisition. This is all done below deck. Besides the scientific side, all the practicalities for life on board stem from the engine room. There are machines for air conditioning, hot water, freezers and waste down here. There is also a separate room of hydraulic equipment for closing watertight doors and using winches and cranes.
Besides the chief, there are 3 engineers, Mike, Joseph and Alexander, as well as 3 oilers, Guillermo, Gregory and Jack and one electrician, Michael. They spend most of their time in the very hot and noisy engine room making sure we are plain sailing as we collect all out data. It was really amazing to see the scale of operations going on just below us, and how much it takes to keep us going, all the way from driving our data acquisition to making sure we have a warm shower.
Besides this fun afternoon, data acquisition is going really well with 3 lines to go! We have had some great weather and made the most of it with dinners on deck and some beautiful scenery of New Zealand when data collection brings us close enough to land.
We commonly get asked about marine life when conducting these sort of scientific studies. The environment is very important to us, and the ship takes this job very seriously. Onboard we have a team of PSOs. This stands for Protected Species Observers who constantly look out for any marine mammals, turtles, and birds.
The PSOs can be found either in the lab or on the observation tower. The observation tower is the tallest point on the ship and is equipped with 2 giant pairs of binoculars. There are 2 PSOs on shift from 30 minutes before sunrise to 30 minutes after sunset, constantly looking out for any species. There is a 500m exclusion zone from all acoustic equipment, within which, if a marine mammal or pinoped is spotted, action is taken. If a mammal comes into the exclusion zone, the pressure of the acoustic waves we are producing is lowered to about 1/10th it’s normal pressure and the exclusion zone is decreased to 100m. If the mammal then enters the new exclusion zone, everything gets shut down. The mammal is monitored, and starting up doesn’t resume again until it has left the exclusion zone. A detailed report is taken of all species seen as well as any changes in behaviour within the exclusion zone and after shutdown. When we turn on the instruments we also do it by ‘ramping up’ which means slowly increasing the pressure, so any mammals can leave the area as the pressure gradually reaches maximum.
PSOs in the lab are using Passive Acoustic Monitoring systems, or PAM, 24 hours a day. This is sort of like a microphone which is towed behind the boat listening out for any mammals. These are usually clicks and whistles which can be used to track the mammals, calculate their bearing, and determine the range. PAM works really well but it’s difficult to identify a specific dolphin species from the clicks and whistles as they sound similar. Other mammals, such as Sperm whales, for example, have a much more distinctive sound.
There are 3 exceptions to shutdowns. The only one we will come across in this region is the common dolphin. A lot of research has been done about this species and it has been found that these curious guys have been known to swim right up to the ship and bow ride for a while, seemingly quite curious about the acoustic instruments. We have been lucky enough to see a few playfully jumping through the waves along the bow! We have also seen many birds, including an albatross or two.
There are 5 PSOs onboard: Amanda, Sara, Brooke, Becky and Mark. While these guys work really hard, they are always happy to let us science crew come up to the observation tower for a look, and let us know if there are any sighting so we can go out and see for ourselves. They are all super knowledgeable about the marine life in the area and have loads of really interesting facts. The whole science party has had a turn wearing the PAM headphones listening to the clicks and whistles of nearby dolphins and it’s really amazing! It’s been a great cruise so far and fortunately no mammals, besides the common dolphin, have come near the exclusion zone, so data collection is going really well!
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.
The science party! Shuoshuo (UT), Ryuta (JAMSTEC), Harold (University of Wisconsin-Madison), Melissa (Imperial College), Dan (GNS), Stephen (University of Wisconsin-Madison), Harry (University of Cardiff), Joel (UCSC), Nathan (UT) and Hannah (University of Hawai’i) [Missing: Time (University of Birmingham)]
Seismometers come in many shapes and sizes. In this project we’re using three types; Guralp 6TDs, GFZ cubes and GeoSpace GSXs. And as the NZ3D team have all had to learn, each is installed differently. The 6TD is our all-singing, all-dancing, self-charging, 3-component broadband quake-measurer. Like a superhero, but one that requires some serious manual labour and technical know-how to put in action…
The 6TD is put to bed in a 60cm deep hole pointing North and precisely levelled using a spirit level. Through a myriad of cables, it is hooked up to a car battery, which is recharged from a solar panel. The GPS records its location and a fence is built around the site to protect it from curious livestock and locals. With soft ground, no technical hiccups and team of keen beans, this takes about two hours (not including the off-roading and site scouting I described last time)!
The cubes, by comparison, are a walk in the park. Literally! They may not be broadband superheroes but we can strap them to our backs and stroll up valleys and across ridges to sites which would be hopeless had we been lugging the amount of gear required for the 6TDs. Plus, all they need is a 10cm hole, a couple of batteries, pop a box over the top and hey presto!
So far everything has gone to plan and we are well on schedule to have all the seismometers deployed by the new year (touch wood). Anyway, it’s not all work and no play for the NZ3D team. We gave ourselves a break to enjoy a summertime Christmas, complete with a BBQ, beach trip and Santa delivering presents to the team! Quite a novelty for the northern hemisphere inhabitants on the team, but certainly not an unpleasant swop!
Here’s hoping our good luck so far spills over into the new year…
And if you just can't wait, catch us on Twitter: @NZ3D_FWI
With our seismometers tested, kit assembled and training complete, we split into five teams and hit the road on a mission to find our first deployment sites. This turned out be easier for some than for others.
In order to acquire a detailed 3D image of the subsurface geology, our seismometers must be spaced roughly 2km apart in a grid across the Gisborne region. But choosing a deployment site is not as straightforward as it sounds.
Our 6TD instruments are made to detect even the smallest of ground movements associated with earthquake activity and are therefore super sensitive to noise such as road traffic rumbling, trees rustling, streams flowing, power lines buzzing, and even electric fences humming. And as the majority of the area is farmland, our biggest contender is the livestock itself. Not only will they generate noise as they amble about the field but curious cows may fancy a nibble on the cables and pull our seismometers out the ground! To combat this we build sturdy fences around our deployment sites.
As if that wasn't tricky enough in rural New Zealand we also have to ensure our solar panels get lots of light and our GPS has a good signal from the satellites. That means no hiding in the bushes. So you can see how finding the perfect spot may take a little time! In fact, our perseverance to hunt down the best deployment sites often means we're splashing through streams along bumpy offroad tracks, strapping our helmets on for a hair-raising ride in an LUV, or when all else fails lugging the equipment up a valley on foot. Our efforts paid off though. Let's just hope that fence holds!
Well, now we've chosen a perfect site, let's put a seismometer in the ground! Wondering what that looks like? Stay tuned...
And if you just can't wait, catch us on Twitter: @NZ3D_FWI
We have lift off! Years of planning, months of preparation and hours of travelling have culminated in a keen team of international scientists assembled in Gisborne ready to investigate the fascinating geology of the Hikurangi subduction zone.
The Hikurangi subduction zone is particularly shallow which makes it more accessible and easier to study than others around the world. It has consequently attracted international interest and funding from scientists attempting to understand plate boundary tectonics and the natural hazards with which they are associated.
Over the next few weeks Project NZ3D will install around 100 seismometers in the Gisborne region. These instruments will record the ground shaking associated with earthquake activity and allow us to image the subsurface structure of the plate boundary lying off the east coast. This research is part of a larger series of projects which aim to help us understand the behaviour of the subduction zone how to minimise the risk posed to communities along the east coast from earthquakes and tsunamis.
The scientific team comprises researchers, technicians and students from far flung corners of the world such as Imperial College London and SEIS-UK as well as those a little closer to home from Victoria University and GNS Sciences. So what did we do on day 1? Recover from jet lag? A spot of sight-seeing? Nope, we got stuck straight in testing the equipment in a garage on an industrial estate... who said science was glamorous? Once we were sure we had everything in order, it was time head to our first field site and practice the full deployment. What could go wrong, right?
Stay tuned, more on this coming soon!
And if you just can't wait, catch us on Twitter: @NZ3D_FWI