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.