Posted by: adorsk | January 29, 2009

New Zealand Seismology

The Thompson left Lyttelton on the morning of the January 29th.  The purpose of this cruise was to place seismic sensors around New Zealand.

First some science.  Why should anyone care about the seismology of New Zealand?  Because it can tell us how the Earth works.  It can help us answer questions like: What happens when two continents run into each other?  Do they make Earthquakes happen?  Do they make certain minerals form?  Seismic data can help geologists answer these questions.  Eventually these answers can help us design warning systems for earthquakes and volcanoes, and locate natural resources.  The fruits of basic research.

New Zealand is an excellent place to study seismology.    It is a geologist’s dream.  It sits atop the junction of the Australian and Pacific plates and consequently is chock full of geological activity.  There are already heaps of data on it.

I should say rather that there are heaps of data on the parts of New Zealand above water.  Unfortunately not much is known about the underwater parts.  That’s why chief scientist JC and his science party were aboard the Thompson.

The Science Party

JC was a geologist from WHOI, originally from Ireland.  He had a rich Irish brogue that carried throughout the computer lab, especially when he was singing.

With JC were geologists PM and AS from the University of Colorado, and graduate student DC.

DT was a middle-school teacher from Colorado who was documenting the cruise for students back on land.  You can see his cruise blog here: http://cires.colorado.edu/science/features/quakecruise/ . Check it out!  Not only does it have haikus, but it has a lot of great things about life on the Thompson.

MC was a marine technician from the Coast Guard who was along as an observer to study deployments.

MG, PG, and EA were three technicians from the Scripps institute of Oceanography.  They were in charge of deploying and maintaining the sensors.

OBSs

Which leads me to the sensors themselves.  The sensors we used were called OBS’s (ocean bottom seismometer).  Their job was to detect jiggling on the seafloor.

This was not an easy job.  An OBS had to detect a range of vibrations, sometimes as small as a millimeter, sometimes as large as a several meters. It also had to be durable.  It would be dropped off a ship, sink down thousands of kilometers to the seafloor, spend a year at the bottom of the ocean, float back to the surface on command, and then be hooked back onto the ship.  An OBS had to be one tough SOB.

The major oceanographic institutions have been designing various models of OBS’s.  On this cruise we used the Scripps ‘L-CHEAPO’ model (Low-Cost Hardware for Earth Applications &  Physical Oceanography).  The L-CHEAPO is quite a clever piece of engineering.

DT has a whole blog post devoted to how it works:

http://cires.colorado.edu/science/features/quakecruise/?paged=14

During this cruise we would deploy 32 of them on either side of New Zealand.

OBSs on the stern of the Thompson

OBSs on the stern of the Thompson

OBS close-up

OBS close-up

The Cruise

The cruise started out with a transit around the Southern end of the South Island.  We were fortunate to have good weather at the start.  The sea wasn’t too rough and we could even see the mountains of New Zealand’s Southern Alps.  It looked like someone had dropped chunks of Switzerland in the middle of the ocean.

the Southern alps of New Zealand

the Southern alps of New Zealand

Marine life was abundant.  Albatrosses wheeled around and around.  Dolphins came by the ship a few times.  Some people even saw penguins swimming past as we rounded the tip of the island.

dolphins off the bow of the Thompson

dolphins off the bow of the Thompson

After a couple days we reached the site of our first deployment in the deep water West of New Zealand.

Deploying an OBS

OBSs were deployed with great care.  The Scripps guys would wheel the next OBS into the ship’s hangar and check out its electronics.  Then they would gently lower it over the side, pull a release, and let it drop to the seafloor.

EA wheels in an OBS

EA wheels in an OBS

the Scripps guys gently lower the OBS over the rail...

the Scripps guys gently lower the OBS over the rail...

...and then yank the release

...and then yank the release

We would track it from the ship using acoustic pings.  When it finally touched down we would get a fix on its position by running a survey around it.

JC pings a descending OBS from the lab

JC pings a descending OBS from the lab

And that’s an OBS deployment!  Repeat 32 times.

Our deployments on the the West side went without incident.  There were a few rougher days but nothing too problematic.  Sometimes we were in sight of Mt. Cook, New Zealand’s highest mountain.  When I first saw it I thought it was just a very high cloud.  All I could see was its snowcap poking out of a cloud bank.  Only when the clouds cleared out did I realize there was entire mountain underneath.

The cruise developed a rhythm.  Normally we deployed three our four OBSs per day, and then did mapping at night before steaming to the next station.

When there was free time between stations people worked in the computer lab, or sat outside on deck.  DT did some fishing for fish with old ham.  Fierce ping-pong games went in the main lab.

DT goes fishing

DT goes fishing

bait

bait

ping-pong in the main lab

ping-pong in the main lab

We finished our deployments on the West side and then transited to the East side through the Cook Strait between the islands of New Zealand.

To the East

We started through the straits in the morning.  At sunrise we passed oil rigs and mountains.  At sunset we went past Wellington, the capitol city on the North Island.

oil rig in the Cook Strait

oil rig in the Cook Strait

lighthouse in the Cook Strait

lighthouse in the Cook Strait

sunset near Wellington

sunset near Wellington

We had a few more deployments to do on the East side.  The weather got a bit rougher, but still the Scripps guys handled it with no problems.

When we finished with the deployments we headed back towards Christchurch and did some mapping near the coast to the South.

And then we were done!  All the OBSs were on the seabed feeling for tremors.  JC and his crew would return in a year to pick them up.  But for now we headed back to Lyttelton to offload and prepare for the next cruise.

back to Lyttelton

back to Lyttelton

You can check out all of my photos from this cruise here:

http://www.flickr.com/photos/adorsk/sets/72157618386386433/show/

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