Consortium for Ocean Leadership, United States

The operational objective of Integrated Ocean Drilling Program Expedition 328 was the installation of a new permanent hydrologic borehole observatory near Ocean Drilling Program Site 889. The format of the new installation followed the Advanced CORK design, which will facilitate pressure monitoring at multiple formation levels on the outside of a 10 3/4 inch casing string. The observatory was successfully installed during the expedition and will allow documentation of 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 gas 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 deformation at the site caused by secular strain and episodic seismic and aseismic slip in this subduction setting. The casing was sealed at the bottom, leaving the inside available for future installation of additional monitoring instruments. At a later date, the observatory will be connected to the NEPTUNE Canada fiber-optic cable for power and real-time communications from land.