Latest Results of formation Pressure Monitoring Using CORKs Penetrating Upper Basement on the Eastern Flank of the Juan de Fuca Ridge

We will report latest results obtained during September 2005 submersible operations at six subseafloor ODP/IODP hydrogeological observatories ("CORKs") on the eastern flank of the Endeavour Segment, Juan de Fuca Ridge. These installations include three original CORKs with long-term basement pressure monitoring, installed during ODP Leg 168 in 1996 on an age transect: Holes1024C in 0.9 Ma crust, 1025C (1.3 Ma) and 1027C (3.4 Ma). They also include three newer multi-level models installed during the first IODP expedition in 2004 in a detailed spatial array above a sediment-buried basement ridge within ~2km from 1027C: 1026B, 1301A and 1301B, with the last two being ~30 m apart ~1km south of 1026B. Previous results with an original CORK in Hole 1026B indicate that uppermost basement in the buried basement are overpressured by ~20 MPa, and the hole can produce formation fluids at ~62circC. This compares to an underpressure of about 25 kPa in Hole 1027C, located off the basement ridge beneath a thicker sediment cover. The new installations in Holes 1301A and B penetrate deeper into basement than 1026B, allowing in Hole 1301B isolation of intervals to 300 m into basement. Thus the array of holes has the potential to document lateral variations in basement pressures plus the vertical variation at 1301B. Previous results from the 1024C-1027C transect have documented in-situ pressures, an apparent age-dependence on large-scale formation permeability, and formation pressure responses to transients ranging from periodic tidal loading to plate strain events. Sampling rates were increased at these installations in 2003, so the new data should be even more diagnostic of formation responses to such transients.