Hikurangi subduction zone expedition #375 – blog 6
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 sixth blog from Aliki Weststrate, IODP (International Ocean Discovery Program) Outreach Educator. This is her account of a voyage full of excitement, challenges and science!
Fur seal
A New Zealand fur seal (kekeno) seen from the Joides Resolution on expedition #375 off the East Coast of New Zealand.
Sub-seafloor observatory deployment complete!
There was a lot of celebrating this week as we finished deploying our second (and final) sub-seafloor observatory. This means New Zealand now has two ‘quake-labs’ sitting under the seafloor in the northern Hikurangi subduction zone.
Observatories are notoriously difficult to install due to the deep water depths and tools required, but we are thrilled both were deployed successfully over the 2-month voyage.
Expedition Co-leader Dr Demian Saffer, Pennsylvania State University
Fault types
Faults types are catorgorised by how the tectonic plates have moved relative to one another. 'Normal' faulting occurs, when the hangingwall block moves down with respect to the lower footwall block while the 'reverse' fault is the reverse - the hangingwall block moves up and over the footwall block. Blocks may also move sideways past each other, this ‘strike-slip’ movement is described as sinistral when the far side moves to the left, and dextral, when the far side moves to the right. Most faults are a combination of fault types.
The location of the first observatory at site U1518 (Te Matakite – see blog 3) was directly into a thrust fault about 60 km east of Gisborne. Research into slow slip events has also pinpointed this thrust fault site as one where these silent earthquakes might be propagating up to the seafloor, so the scientists chose to position the observatory instruments below, within and above the fault.
Top of the Te Matakite observatory
A cutaway diagram showing the top section of the first observatory, Te Matakite. The rectangular platform sits on the seafloor. Down below this, the temperature, pressure and chemistry instruments are hanging vertically into the borehole down to 450 mbsf (metres below seafloor).
A cutaway diagram showing the top section of the first observatory, Te Matakite. The rectangular platform sits on the seafloor. Down below this, the temperature, pressure and chemistry instruments are hanging vertically into the borehole down to 450 mbsf (metres below seafloor).
Slow slip events are an enigmatic phenomenon, only recently discovered by geologists studying Earth’s movement almost 20 years ago. They appear to bridge the gap between typical earthquake behaviour and gradual creeping plate movement.
In the northern Hikurangi region, they occur with remarkable regularity – approximately every 2 years and last over a period of 2–3 weeks at shallow depths (<5–15 km below the seafloor).
Location of the second observatory
This seafloor maps shows the third site U1519, where the second and final observatory was installed. It sits above the sedimentary basin on what scientists call the upper plate boundary.
The second observatory at site U1519 was closer to shore, about 30 km east of Gisborne. This site was chosen for the observatory because it is very close to the location of a March 1947 earthquake epicentre. This earthquake had low-intensity shaking and was hardly felt on land yet caused a 10 m local tsunami to hit the East Coast, damaging many roads and bridges. The tsunami affected 120 km of coastline from Tokomaru Bay to Mahia Peninsula .
It still perplexes geologists that the shaking wasn’t felt strongly on land yet there was enough uplift of the seabed near the subduction trench offshore to cause a significant tsunami in this area. Installing another observatory into the slow slip source area above the upper plate boundary might shed some light on how and why this occurred.
It’s fascinating to watch Earth scientists from 10 different countries work together to solve the puzzle of slow slip earthquakes here at the Hikurangi subduction zone.
Aliki Weststrate, IODP Outreach Educator
The puzzle of the Hikurangi Subduction Zone
We are putting together a puzzle on expedition #375 to study earthquakes in the Hikurangi subduction zone. We are using seismic surveying and logging while drilling (LWD) data collected before our expedition to help us know where to core and install observatories.
Amazing animals and fun distractions
We’ve been visited by a large pod of dolphins, loads of albatross and seabirds, a fur seal and pilot whales, and a large sunfish drifted by one day, just under the surface.
We are fortunate to have seen a lot of sealife during our 2-month expedition. Watching a pod of pilot whales cruise by this week was a highlight.
Aliki Weststrate, IODP Outreach Educator
Wildlife seen from ship
This week a pod of dolphins, fur seals and an albatross (toroa) have been seen from onboard Joides Resolution.
We caught some incredible footage of squid this week too – you can watch it here. They are Humboldt squid and are known to attack their own species, but it’s rare to see it on film.
We also celebrate birthdays by having a cake, and on sunny days, we do it outside and have a BBQ near the bow of the ship. Some musical scientists have started a band that makes up songs for people’s birthdays – they’re hilarious.
Expedition #375 band
A good way to enjoy leisure time after your shift is to play an instrument. Some science crew have got together and formed a band, specialising in original birthday songs.
Related content
This article gives some background to the scientific research vessel JOIDES Resolution.
Read Aliki’s other blog articles here.
Learn more slow slips and the different types of faults in the Earth’s crust and volcanology methods.
This interactive diagram provides a selection of pathways that allow for differing approaches and starting points using our earthquakes resources.
Useful links
Watch rare footage of Humboldt squid captured by the IODP underwater camera.
The ANZIC IODP Consortium has a Youtube channel showing short videos explaining past and present expeditions and information.
Acknowledgement
This article was written by staff at GNS Science working as part of the ANZIC IODP Consortium.
GNS Science
GNS Science, Te Pū Ao, is New Zealand’s leading provider of Earth, geoscience and isotope research and consultancy services. Its purpose is to understand natural Earth system processes and resources and to translate these into economic, environmental and social benefits.
