Hikurangi subduction zone expedition #375 – blog 2

In March 2018, JOIDES Resolution, a large scientific research vessel, headed out to sea to research the Hikurangi subduction zone on expedition #375. This article is the second blog from Aliki Weststrate, IODP (International Ocean Discovery Program) Outreach Educator. This is her account of a voyage full of excitement, challenges and science!

Getting into the swing of ship life

Week 2 on board the science vessel JOIDES Resolution has definitely been easier. We’re all sleeping better as we adjust to the movement of the ship. I’m finding it easier to wake up at 11.30pm for my 12-hour shift too, which is midnight to noon. Most people have a pattern of going to the gym, working, then going up to the top deck for some sun or watching a movie in the lounge.

We haven’t seen any whales or dolphins, but we do see lots of albatross and fish. One day, I came out to see a double rainbow behind the derrick – it was beautiful.

Connecting with schools

One of the reasons I am on the midnight to noon shift is that schools from around the world can Zoom us (like Skype) in their daylight hours. My job as an Outreach Officer is to take them on a tour of the ship, showing them the amazing drill tower (derrick), the lifeboats and inside to the high-tech laboratories on board the research vessel.

Where are we?

We are located about 70 km off shore of the east coast of New Zealand – near Tolaga Bay above Gisborne. The main purpose of this site is to take core samples from under the seafloor, and this will give clues in order to understand how the layers change from the top, through the fault zone to the bottom of our drill hole. We are looking at the sediment to understand its chemistry and what that tells us, its physical properties (how dense, how wet, how brittle), its temperature and whether it contains fossils that help us date it.

What have the scientists been looking at?

We spent the first week at site 1 busily coring down under the seafloor to about 500 metres (in 2,700 metres of seawater). The core comes up faster than the scientists can analyse it, so it was only in the first part of week 2 that they split in half the cores from the actual fault. The excitement and discussion about the fault zone cores was intense. It is not often we can access core samples of a fault from under the ocean.

The excitement and discussion about the fault zone cores by the scientists and engineers was intense. It is not often we can access core samples from under the ocean of a fault

Akiki Westrate

Site 1 is where the frontal thrust of the Hikurangi subduction zone is located. This is a fault that splinters off from the main Hikurangi subduction zone fault below, and it runs vertically almost all the way to the seabed. It is sometimes called a hanging wall because it sits above.

This whole area is part of the Hikurangi subduction zone where two huge tectonic plates collide – the Pacific plate is diving down under (subducting) the Australian plate. The image above is a seismic map. It is similar to an ultrasound and shows scientists the inside of the Earth as a cross-section. The black line at U1518 is the first drill site. The line shows how deep the drill went – it crosses the red fault that stretches up to the seafloor. By drilling here, scientists can pull up sediment directly from the fault zone to study.

Our site and this whole area near Gisborne is interesting because, just after the M7.8 Kaikōura earthquake in 2016, it set off a slow-slip event here. This set the whole region shaking slowly like jelly in a bowl, but so slowly that people couldn’t feel it – only GPS could. It is also one of the shallowest subduction zones in the world, making it possible for an Earth science ship like JOIDES Resolution to drill into and study it.

Next mission – launch an observatory!

Later in the week, I spoke to people who are doing the final preparation of the CORK observatory, which we will finish installing next week. It’s such an amazing instrument – it will sit 450 m under the seabed, and the measuring equipment is designed to sit exactly in the fault zone itself (which is only about 20 m wide). It is a mixture of ancient mariner knowledge, modern materials, science and technology.

It is essentially an outside steel casing lowered down into a predrilled hole, and inside are three different ‘packages’ of equipment. Each package is designed to sit exactly at the right depth to measure chemistry, temperature and fluid pressure through the fault zone for the next 5–10 years. Installing it while the ship is moving and in a water depth of 2,700 m is not easy! Each package has to sit inside the other, like a Russian doll, so it goes down in three stages. An engineering feat for sure!