%0 Journal Article
%T IODP Expedition 328: Early Results of Cascadia Subduction Zone ACORK Observatory
%A Earl Davis
%A Martin Heesemann
%A the IODP Expedition 328 Scientists and Engineers
%J Scientific Drilling
%D 2012
%I Copernicus Publications
%R 10.2204/iodp.sd.13.02.2011
%X Integrated Ocean Drilling Program (IODP) Expedition 328 was devoted to the installation of an ˇ°Advanced CORKˇ± (Circulation Obviation Retrofit Kit) in the Cascadia subduction zone accretionary prism to observe the physical state and properties of the formation as they are influenced by long-term and episodic deformation and by gas hydrate accumulation. Pressures are monitored at four levels on theoutside of a standard 10 -inch casing string, two above and two below the base of the gas-hydrate stability zone at 230 mbsf (m below seafloor). The casing was sealed at the bottom, leaving the inside open down to 302 mbsf for installation of a tilt meter, seismometer, and thermistor cable (scheduled for 2013). The initial data, recovered in July 2011, document an initially smooth recovery from the drilling perturbation followed by what may be a sequence ofhole-collapse events. Pressure at the deepest screen is roughly 40 kPa above hydrostatic; higher pressures (80 kPa)are observed at the two screens close to the level of hydrate stability. Tidal variations at the deepest screen are in phase with ocean tides, and define a loading efficiency of 0.6, which is reasonable in light of the consolidation state of the for-mation (porosity ~0.5). Tidal signals near the level of gas hydrate stability display large phase lags, probably as a consequence of hydraulic diffusion stimulated by thelarge contrast in interstitial fluid compressibility at the gas-hydrate boundary. The degree of isolation among the screens, the anticipated good coupling, and the estimated strain-to-pressure conversion efficiency (~5 kPa ¦Ěstrain-1)indicate that this installation will serve well to host a variety of hydrologic, seismic, and geodynamic experiments.
%K Cascadia
%U http://www.iodp.org/index.php?option=com_docman&task=doc_download&gid=3399