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doi:10.2204/iodp.sp.328.2010 AbstractOperations to be carried out during Integrated Ocean Drilling Program Expedition 328 will be devoted to the installation of a new permanent hydrologic observatory at Ocean Drilling Program (ODP) Site 889, the location originally chosen for a Circulation Obviation Retrofit Kit (CORK) installation during ODP Leg 146. During that attempt, rapid sediment intrusion into the perforations and bottom of an open-ended casing liner prevented proper sealing of the hole, and the objectives for the original CORK monitoring were never met. The format of the new installation will follow the Advanced CORK (ACORK) design, developed initially for installations at the Nankai subduction zone during ODP Leg 196. This configuration will facilitate pressure monitoring at multiple formation levels on the outside of a 10¾ inch casing string. The casing will be sealed at the bottom, leaving the inside available for future installation of additional monitoring instruments. Although drilling operations will be highly focused in a short period of time on site, a broad range of objectives will be addressed with monitoring over the decades to follow. These will include documenting the average state of pressure in the frontal part of the Cascadia accretionary prism, the pressure gradients driving flow from the consolidating sediments, the mode of formation of gas hydrates, the influence of hydrates and free gas on the mechanical properties of their host lithology, the response of the material to seismic ground motion, and the magnitude of strain at the site caused by episodic seismic and aseismic slip in this subduction setting. Initial instrumentation will include autonomously recorded seafloor and formation pressure sensors and seafloor temperature sensors. These, and other downhole instruments to measure temperature, tilt, and seismic ground motion to be deployed at a later date by submersible, will be connected to the NEPTUNE fiber-optic cable for power and real-time communications from land. | ||
