Science AMA Series: We’re scientists on board the JOIDES Resolution for IODP Exp 375 to understand slow slip events at the Hikurangi Subduction Zone, east of New Zealand. We will be coring at four sites, and installing two observatories to better understand these types of earthquakes. AMA!

Abstract

The JOIDES Resolution (JR) is a research vessel that drills into the ocean floor to collect and study core samples. Scientists use data from the JR to better understandsubseafloor geology, tectonic processes, hazards, climate change, and Earth’s history.

The long subduction zone that extends down the east coast of the North island is called the Hikurangi Subduction Zone. The Hikurangi Subduction Zone is poorly understood, yet potentially the largest source of earthquake and tsunami hazard in New Zealand.

It is also the best place to study slow slip events (also referred to as “slow earthquakes” or “silent earthquakes”). Slow slip events (SSEs) are where movement between the tectonic plates occurs slowly across the subduction zone, over a period of weeks to months, rather than suddenly in a large earthquake.

The world’s shallowest slow slip events occur just offshore of the North Island’s East Coast, near Gisborne, and so are an ideal place to bring the science and drilling capabilities of the JOIDES Resolution to understand why they occur.

Expedition 375 will be positioned in this area from March-May 2018 extracting drill cores for analysis and inserting observatories into two of the drill holes to investigate the processes and the conditions that underlie slow slip events. These instruments will form a long-term offshore observatory to monitor the Hikurangi Subduction Zone and improve our understanding of this large undersea fault system. Read more here: http://joidesresolution.org/expedition/375/

The scientists on board who will be answering your questions include:

Dr Demian Saffer is a Co-Chief Scientist on board Expedition 375. He is a Professor at Pennsylvania State University and his research areas include active tectonics, fault/sediment mechanics and geohydrology.

Dr Katerina Petronotis is the Expedition 375 Project Manager and works as a Staff Scientist at the International Ocean Discovery Program at Texas A&M University. Her research areas include Pacific Plate motions, hotspot geodynamics, nature of the geomagnetic field, and rock magnetism.

Dr Steffen Kutterolf is sailing as a core describer on board Expedition 375. His research areas include sedimentology, volcanology, geochemistry, and tephrochronology.

Dr Francesca Meneghini is sailing as a core describer on board Expedition 375. Her research areas include sedimentology, structural geology, active tectonics, and rock mechanics.

Aliki Weststrate is a freelance science communicator and teacher. Her role on this expedition is to facilitate Education and Outreach between the crew onboard the JOIDES Resolution and the outside world.

​Ask Us Anything!

Hello expedition members!

My question is for the science members on board. I will be participating as a member of the physical properties team on an upcoming expedition (#379) and was mostly just curious how the experience has been for you all so far? Any advice you might want to pass along would be greatly appreciated! I have participated in many field campaigns in Antarctica, but never offshore on a research vessel, so this will definitely be a new experience for me.

Thank you all for the great science you are all doing and I look forward to reading through this AMA to learn more specifically about the expedition and your experiences so far.

lakewoodhiker

This experience is probably a little different for everyone out here. What makes it fascinating to me is that so many people from different countries and cultures come together to address a scientific question. And we do so by producing a huge data sets in 2 months that would take several years for all of us to produce on shore. What makes it challenging is working long shifts (12 hours per day) over several weeks and learning to communicate and work harmoniously with each other. However, scientists keep coming back to IODP expeditions so the experience is usually rewarding during the expedition and even more so for scientists' post-expedition research plans.

To answer your question more specifically, working on the JR will probably not be that different from field work in Antarctica, except the rocks arrive on the ship in long plastic tubes and the ground moves!


What do you hope to find?
And what would surprice you the most?

GISP

At the moment we are collecting different types of data such as the types of sediments and rocks present below the seafloor and their physical properties, the age of the sediments, and the chemistry and types of fluids moving through the sediments. Together with the data collected during the expedition and the results from experiments conducted on shore in the years to come, we hope to understand why this part of New Zealand experiences the type of earthquake known as a slow slip event. Slow slip events occur in a few places on the planet and result in the land moving continuously over a few weeks with no noticeable shaking on land.

We have some idea of what is beneath us based on seismic data collected before the expedition. However, we need the cores we have been collecting to groundtruth those predictions. For example, at the site we are at now (Site U1520), we drilled down to 1055 m (3482 feet) and recovered a range of sediments and rocks, some of which were unexpected.


What type of observations are you hoping to make from the sediment extracted from the cores? I.e. are you hoping to characterize their mechanical properties? Sedimentalogical records of slow slip events?

What's included in the observatories? I'm assuming seismometers, but anything else?

CrustalTrudger

There are different approaches here since the background of the shipboard sedimentologists is broad. It includes working on depositional processes of the seafloor slope and the respective emplacement processes of the sediments (e.g. turbidites) to very specific questions like for example when explosive volcanism started in New Zealand and if there are systematic patterns of occurrence (tephra) observables in the sedimentary record, or how the clay mineralogy changes within the formation. We are also interested in characterizing the rocks and sediments from a structural point of view, by analyzing the different deformation processes at different depths. This, together with measurements of various physical properties across the cores, and geochemical analyses, will give us information on the mechanical properties of sediments and rocks, and test our hypotheses on rock fault behavior.

The observatories include three sets of instruments: (1) pressure sensors to monitor fluid pressure in the formation at three different depths - these will provide a sensitive measure of volumetric strain (compression or extension) associated with fault slip, including slow slip events; (2) a "string" of temperature sensors suspended in the well to monitor any changes in temperature associated with fault movement or variations in fluid flow; and (3) chemical sampling devices to collect a record of fluid composition over time - again designed to gain insight into changes in the "plumbing" of the plate boundary system before, during, or after slow slip events.

There are actually no seismometers in the observatory - this is for two reasons. First, the dominant style of fault slip here, and the phenomenon we are studying, is slow slip. These events unfold over several weeks, and radiate little or no seismic energy - so are largely "invisible" to seismometers. Second, and perhaps more importantly, the power demands and data volume produced by seismometers are too large for us to include such instruments in the observatories, because they are standalone installations without any cabling or external power. Having said that, there are a number of allied campaigns that include the deployment of several ocean bottom seismometers that have been or will be, deployed for a few months at a time.


How long will the observatories be able to collect data, and how do you retrieve the data?

Menthol22

The observatories are designed to record pressure data on data loggers that are mounted on the wellhead, at the sea floor. To retrieve the data, we will need to return to the site in a few years with an ROV (ROV stands for remotely operated vehicle - essentially an unmanned robotic submarine). At that time we will plug in to the data logger and download the data, basically in the same way as you would copy data from a USB drive, except that the connections are all made using very robust and water- and pressure-proofed underwater connectors designed to withstand the pressure of >2000 m of overlying water. The main limitation on the pressure measurements is the battery life, which is approximately seven years. We expect to come back before that, depending on the availability of research ships and ROVs. We also hope to replace the pressure sensors and battery package before the seven years elapse; this is possible because the package is modular and can be removed and a replacement package swapped in.

The chemical samplers and temperature sensors are suspended in the borehole and are autonomous. To get the data from the temperature sensors, or to recover the fluid sampling systems, we will need to return with an ROV, connect the top of the sensor string to a cable, and use the ship's winch to pull the 400 m-long string of sensors and samplers out of the hole. We are planning to recover these sensors at the same time that we return to download the pressure data, ideally in 3-5 years. Like the pressure sensors, it will also be possible to install a replacement interment string for fluid sampling and temperature monitoring, basically by doing the reverse of the recovery procedure: the string would be lowered on a cable, an ROV will guide the end of the string into the borehole at the seafloor, and then the string will be lowered into place.


So most of the observatory data won't be accessible until ca..5 years from now ?

iceseismic

That's correct plus it will take some time to publish the data. The exact timing will depend on when we can return to download the pressure data and recover the temperature loggers and chemistry package.


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