Preparing for coreMay 16, 2012
The expedition is now gearing up to retrieve core samples from the interval of rocks that surround the plate boundary fault surface at the Japan Trench. Core samples will be retrieved from an approximately 200m long interval at a depth of almost 8km below sea level. These will become some of the deepest core samples retrieved by the Scientific Ocean Drilling Program. The coring process is like sticking a straw into a bowl of Jello, and then pulling up the bit of Jello stuck in the middle (the rock core). To think of the process at a scale comparable to the drilling operations here, however, you would have to imagine standing on the roof of the Empire State Building with a straw that extends down to street level.
To retrieve the core, about 8 km of drill pipe are assembled and lowered from the rig floor to the sea floor. The pipe has a drill bit attached at the tip that has a hollow center, where the core sample is preserved. The drill bit will advance through the rock until a ~10m interval has been sampled. This core remains in the core barrel inside the drill pipe until it is brought back to the surface by a wire line.
< There are many different types of drill bits for coring. Here is the kind that we are now using for the Chikyu drilling. The hollow tube in the center is where the core is preserved >
Once the cores arrive on deck, the samples will be measured, catalogued, cut into 1.5m sections, and split in half lengthwise. The core is described visually for sedimentologic, mineralogic, and structural components, as well as drilling induced damage. Samples are taken from the core to determine the physical and chemical properties of the rocks, and for study of microbiologic activity. Many of these samples will be analyzed in ship-board laboratories for properties that include electrical resistivity, porosity, moisture content, chemistry of pore waters, paleomagnetism, Hydrogen and Methane content, and thermal conductivity. Many additional samples will be sent back with the scientists to their respective labs for continued experiments and analyses after the cruise.
All the core sampling tools were laid out on the work bench as the scientists were trained in sampling methods
Small flags are placed to mark the location in the core where samples are taken. Each flag has a code for the type of sample
Analysis of the core requires the expertise of a wide range of scientists and laboratory technicians. All of the core data will be logged in IODP reports that become publicly available (you can see past reports at http://www.iodp.org/scientific-publications/). These data will provide invaluable information about the physical properties of the rocks in and around the fault zone and the processes that lead to the occurrence of large magnitude earthquakes.
Arriving at the borehole siteApril 4, 2012
This morning at 8 am, after 41 hours of transit, we arrived at the location of our first borehole. I was able to track our route with a hand-held GPS from the port at Shimizu to our current location at JFAST 3, located about 250 km east of Sendai. It was nice to be able to watch our progress on the GPS map. We had little way of knowing our position otherwise because we were far from shore and could only see the ocean for miles.
Map of our route from Shimizu to the borehole site.
This is my first time at sea, and I wasn't sure what to expect in terms of sea sickness. For the first day, the motion of the boat was so slight that I had a hard time discerning weather or not it was even real. It's a very odd effect because you have no stationary reference frame inside the boat. It kind of feels like you are in a flight simulator at an amusement park. Your body feels the change in acceleration with every wave, but because everything in the room is moving with you, your mind does not know how to process the motion. It can be very disorienting until you get used to it, and I have stumbled off my feet a couple of times in big waves. It is actually is much easier to handle when you are out on deck or looking out of a window and can see the horizon.
Unfortunately, some bad weather has moved in today and we cannot start operations until the waves calm down. As of this afternoon there were swells of ~5m, and it is likely that they will be up to 10-15m by night. Already the boat is rocking with quite a fervor, and the drilling derrick (tower) is making an eerie, grinding, metallic noise as it compensates for the ship's movement. Luckily, we've had two days to get somewhat acclimatized to the constant motion. In addition, the Chikyu is a very large boat, and is quite stable in comparison to smaller vessels. But I think we will all find out tonight just how good our "sea legs" are.
This computer monitors the pitch and roll of the ship.
As we prepare to begin drilling operations, the scientists on board have been taking part in many discussions about the project, how we want to position the boreholes, and what data we can use to definitively locate the fault zone. In addition to scientific discussions, we were able to get a tour of the drilling operations portions of the ship. The engineers, drillers, and mechanics have tough jobs and it is because of their work that we can even hope to be able to examine data from this fault zone. It was great to get to see their work stations and thank them for their efforts.
Members of the science party get a tour of the drilling operations.