Sunset on HOBITSS voyage

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sunset-panorama2

 

Today we returned to the Napier port. We were pleased to have a very successful voyage, with 34 out of 35 ocean bottom instruments retrieved, and 100% recovery of ocean bottom seismometers and pressure sensors. In the next months and years we will be busy analyzing the data to learn more about earthquakes, plate tectonics, and slow slip of the Hikurangi margin offshore Gisborne and Napier, New Zealand. We thank Captain Tom Desjardin and the crew of the R/V Roger Revelle for a safe and successful voyage, and we think you, our blog readers, for checking in and sharing in our adventure.

Science crew of HOBITSS voyage.

Science crew of HOBITSS voyage.

 

 

Guest Blog Post from Cruise Chief Scientist Laura Wallace

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Greetings from the final stages of the HOBITSS cruise. My name is Laura Wallace, and I am a Research Scientist from the University of Texas Institute for Geophysics. I have been studying slow slip event processes on the Hikurangi subduction zone for over a decade, mostly using land-based measurements with Global Positioning System (GPS) data from New Zealand’s GeoNet network (www.geonet.org.nz). I started working on Hikurangi slow slip when I was working for GNS Science in Lower Hutt. It has always been a dream of mine to do offshore investigations of slow slip here, and I’m glad this is finally coming true with the HOBITSS project.

I am really excited to say that we have recovered our instruments, and that the vast majority of them have great looking data! This is a massive relief to me, as it is always a gamble when you drop instruments on the seafloor. As the OBS team from Columbia University always tells me, there are lots of things that can go wrong. I had a few sleepless nights in the lead-up to the cruise, worrying about what could go wrong.   Luckily most of these things didn’t happen.

The recovery of the instruments is also very exciting because a large slow slip event occurred in late September/early October directly beneath our network of Ocean Bottom Seismometers and Absolute Pressure Gauges.   We are excited to start analyzing the pressure data to see if we can detect vertical deformation of the seafloor during the slow slip event. This will allow us to map out the offshore distribution on the shallowest part of the plate boundary (<10 km) for the first time ever. Based on the land-based GPS measurements during the slow slip event, we expect 1-4 cm of uplift of the seafloor over much of our HOBITSS network.

The seismologists on board are already finding lots of earthquakes on both the Ocean Bottom Seismometer and Pressure Gauge data, although it will take many months of analysis to get the full results from the project. We have a great science party on board, with lots of enthusiastic graduate students. The most valuable members of the team by far, though, are the seafloor instrument engineers from Columbia University, University of Texas, Tohoku University, and University of Tokyo. Those are the guys that make sure we get the instruments and the data back safely. Drew Cole and Jay Turnbull are the Resident Technicians on board the R/V Roger Revelle, and they have also played a major role in making sure things go smoothly during our operations.

I’m used to doing land-based fieldwork, so being on a ship is quite different for me. I have to say I’m really enjoying it! The cruise has been fun, but I can’t wait to get home and start working on this data!

Drew Cole oversees recovery of one of the Columbia University OBS

Drew Cole oversees recovery of one of the Columbia University OBS

The Science Party anxiously waiting to get a signal from one of the instruments that has been on the seafloor for over a year

The Science Party anxiously waiting to get a signal from one of the instruments that has been on the seafloor for over a year

The OBS team from Columbia University

The OBS team from Columbia University

Yoshihiro Ito and his team from Kyoto University, admiring their instruments

Yoshihiro Ito and his team from Kyoto University, admiring their instruments

All the University of Tokyo instruments lined up after their year on the seafloor beneath Poverty Bay

All the University of Tokyo instruments lined up after their year on the seafloor beneath Poverty Bay

My University of Texas instruments lined up on the deck!  So happy they came back.

My University of Texas instruments lined up on the deck! So happy they came back.

GPS-Acoustic

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gps_a_blog

The GPS acoustic system being installed on deck.

Last night we towed a buoy behind the ship to make GPS-Acoustic measurements. Here is a description of the method from Kido et al., Geophysical Research Letters, 2011:

“The GPS/acoustic technique, which was proposed and

developed by the Scripps Institution of Oceanography

[Spiess , 1985], consists of two essential components: the

kinematic GPS of a surface platform, and acoustic ranging

between the surface platform and an array of seafloor

transponders. As introduced by Kido et al.  [2006], we used a

towed buoy navigated near the center of the transponder

array as the surface platform during a campaign (hereafter

called a stationary survey). The shape of the transponder

array is assumed to be rigid through repeated campaigns

over the years because of its relatively short baseline. With

the assumptions that sound speed in the ocean is laterally

stratified and that the seafloor moves only in the horizontal

direction, the horizontal position of the array and the mean

sound speed from the sea-surface to the bottom can be

determined with a single acoustic ping of simultaneous

ranging to all the transponders [Kido et al. , 2008]. The

temporal position of the array is then obtained as a time

series for thousands of pings. The final position of the array

in a campaign is determined by averaging the fluctuations in

these time series, which are presumably due to undesired

spatio-temporal variation in the sound speed beyond the

stratified approximation. The resultant accuracy of array

positioning in a single campaign is typically 5 cmdepending

on the ocean conditions and duration of the survey.”

With this method we can make very precise measurements of a position on the seafloor, and by repeating measurements over several years and comparing them with sites on land, can measure the motions of the tectonic plates and motions associated with large earthquakes. Similar seafloor GPS-acoustic measurements were made before and after the 2011 Japan Tohoku-Oki earthquake, and found displacements of the seafloor by 31 meters horizontally, which is huge.

Conductivity Temperature Depth (CTD) probe being lowered into the water. This instrument measures the electrical conductivity of the water (which is related to salinity) and the temperature of the water as a function of depth as it is lowered into the water. Both of these parameters affect sound speed in water, and need to be accounted for to accurately position the seafloor GPS array.

Conductivity Temperature Depth (CTD) probe being lowered into the water. This instrument measures the electrical conductivity of the water (which is related to salinity) and the temperature of the water as a function of depth as it is lowered into the water. Both of these parameters affect sound speed in water, and need to be accounted for to accurately position the seafloor GPS array.

Riding the waves

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A big wave at the back of the ship. Photo courtesy Justin Ball.

A big wave at the back of the ship. Photo courtesy Justin Ball.

We had to temporarily suspend our instrument recovery operations for a day while waiting for a storm to pass. This video shows the waves we rode the past few days. The first view is from 23 June with 4-5 meter swells, the second view is from 24 June when the wind started to pick up, and the last view is from yesterday when the rain really started coming down. The weather is much better today!

http://youtu.be/VDV7ybhpvLk

 

Safety, Safety, Safety….

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In addition to the safety induction we had before leaving Napier, we are all required to try on an immersion suit. These suits, also called Gumby suits, are designed to prevent hypothermia in the event that a person ends up in the water. Since they are difficult to put on, all members of the science party are required to try them on during the voyage. Once in these suits, it’s difficult to do much with your hands.

safety gear

Tom demonstrating his safety gear

Putting on the Gumby suits

Putting on the suits

Putting on the suits

Your non-dominant arm has to go in first so you can get the rest of the suit on

Putting on the suit

To zip the suit with one hand in the suit, you have to lean back as far as possible

Gumby!

The end result is a brightly colored, very warm Gumby!

After we had completed our safety training (putting on the immersion suits for practice), Free Bird happened to be playing in the background. How could we resist??

Scenes from around the ship

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Here are a few photos from around the ship. Seismometer retrievals and deployments have continued to go forward as wind and swell cooperate.

Lamont ocean bottom seismometer on deck

Lamont ocean bottom seismometer on deck

Heather the second mate.

Heather the second mate.

Mark the cook - he keeps us well fed and happy

Mark the cook – he keeps us well fed and happy

Derek the AB, galley behind.

Derek the AB, galley behind.

Ocean bottom seismometer deployment at night.

Ocean bottom seismometer deployment at night.

Graduate student Satoshi from Kyoto University

Graduate student Satoshi from Kyoto University

Lamont ocean bottom seismometer on deck. This is the shallow trawl-shielded kind.

Lamont ocean bottom seismometer on deck. This is the shallow trawl-shielded kind.

Tony the computer IT specialist. We have a limited internet quota each day.

Tony the computer IT specialist. We have a limited internet quota each day.

Meet Tom – the token Kiwi!

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Hi my name is Tom Wilson, I am a postgraduate geophysics student at Victoria University of Wellington (VUW). Early this year I received an email recruiting a kiwi postgraduate geophysics student to help out with the HOBITSS project. I instantly replied expressing my interest, and to my delight I was accepted. I was stoked, its not everyday you get news you get to be involved with a collabrative multi-national research project!

Tom hard at work

Sailing day, the 20th June, came around quickly and it was time to set sail. I was all stocked up with seasickness medicine and a sunny optimism that I wasn’t going to need it. A few hours before setting sail I took them as a precaution anyway. I’m glad that I did. It was on the very first night that I had my first proper encounter with sea sickness. Needless to say it wasn’t fun. I found that motion sickness quietly creeps up and takes hold. All you can really do when it hits is wait it out and try and keep your fluid intake up. I also found that keeping busy helps a lot! It is now day 4 and I am feeling adjusted to life on the sea. I am glad to say that you do adjust to the constant rocking and rolling of the boat!

Splashing off the stern

Photo taken on 22 June. View off the back of the ship from inside the hanger. Significant wave height of 5.0m at the time this photo was taken

As the night went on the waves got higher…

Significant Wave Height

Significant Wave Height reached 5.1 m on 22 June

A bit of weather

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The sea state has picked up a bit, so the rate of deployments/recoveries has slowed. It is good that we got so much done during the first 48 hours of the cruise. We picked up 4 out of the 5 shallowest seafloor pressure recorders, which is important as calm seas are needed for that work. It is 2:30 am now, and we are nearing the drop site of one of the Kyoto University seafloor pressure gauges. Yoshi Ito and Res Tech Jay will assess whether it is safe to deploy soon, and if not, we will move on to another site to the south and wait until morning. Deployment in high seas is easier than recovery. For recovery of the OBS there is more of a chance of it banging into the ship and getting damaged, and personnel have to be on deck longer to snag the instrument.

Chief Scientist Laura Wallace on the bridge

Chief Scientist Laura Wallace on the bridge

Ted and Jay on deck

Ted and Jay on deck

The little white ball is a buoy that is connected to the shallow seafloor style of bottom pressure recorder

The little white ball is a buoy that is connected to the shallow seafloor style of bottom pressure recorder

Seafloor pressure sensor emerging from the deep

Seafloor pressure sensor emerging from the deep

Relieved scientists happy to the instruments back on board

Relieved scientists happy to see the instruments back on board

Seafloor pressure sensor on deck. It is covered with mud and barnacles from a year on the seafloor.

Seafloor pressure sensor on deck. It is covered with mud and barnacles from a year on the seafloor. Thanks to Justin and Erin for their hard work cleaning off the stinky muck.

Anne, Spahr, and Martha on deck.

Anne, Spahr, and Martha on deck.

 

 

OBS aboard!

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The video linked below shows the recovery process for an ocean bottom seismometer and absolute pressure gauge from the Lamont-Doherty Earth Observatory at Columbia University in New York.

Click here.

Once the instrument is recovered, it needs to be washed and disassembled in order to retrieve the data.

LDEO_OBSspecs

First ocean bottom seismometers recovered

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Harbor pilot escorts us out of Napier Port and Harbor

Harbor pilot escorts us out of Napier Port and Harbor

Rainbow as we start our voyage

Rainbow as we start our voyage

Guest post from Teddy K:

Winter Solstice, Sunday 21 June 06:50 local,

38S. 178E.

Last vestiges of NY time zone. Works out well though, 07:30 we will start to pick up
the first of 5 Lamont TRM/BPR’s. (Smaller version of the big steel hulks we have worked on).
Two Texas BPR’s, (Bottom Pressure Recorders), are on board. One washed up ashore a few months ago but was still recording. Second one, we picked up last night. Still recording, but it’s strobe light and radio were not operational. Real hard to find in the dark while it’s blowing 25-30 knots, in Beaufort 4-5 seas.

Rest of the night was spent picking up Japanese OBS/BPR’s. 5 recovered and on board.

Weather has moderated, wind down to 20Kts., and not as lumpy.
We’re looking at a long day as we want to recover all 5 Lamont TRM/BPR’s in daylight as they do not have radio’s or strobes. Sunrise is ~ 07:30 as the shortest day of the year is 22June, Winter solstice
down here.

——

1626 update (Anne)

Excellent success so far – 8 instruments total recovered – 1 Texas bottom pressure recorder, 2 ERI (Earthquake Research Institute, University of Tokyo) ocean bottom seismometers, 2 ERI bottom pressure recorders, 1 JAMSTEC (Japan Marine Science Agency) ocean bottom electromagnetic sensor, 2 Lamont shallow trawl mounted ocean bottom pressure recorders. In addition one Texas bottom pressure recorder washed up on shore a couple months ago and is on the ship now – it kept recording the whole time. One shallow Lamont bottom pressure recorder did not come up when we sent the command this morning, though we could communicate with it, so we will try again later in the cruise. The buoy for one more Lamont bottom pressure recorder has just surfaced and will be on board shortly. We have been working in shifts 24 hours a day in order to maximize the science that we can do during our voyage. We are also trying to get as much work done while the weather is good – absolutely beautiful sunny day today, calm seas.

First seismometer retrievals were at night.

First seismometer retrievals were at night.

Seismometer is spotted in the dark sea - strobe light and radio help.

Seismometer is spotted in the dark sea – strobe light and radio help us locate it.

Seismometer (the orange ball) near the ship.

Seismometer (the orange ball) near the ship.

Poles with hooks and rope to grab the seismometer.

Poles with hooks and rope to grab the seismometer.

Ocean bottom seismometer connected to rope.

Ocean bottom seismometer connected to rope.

Seismometer safely on board.

Seismometer safely on board.