SITE SUMMARIESSite: H2O-4
Position: 27°53.298´N, 142°00.456´W
Water Depth: 4980 + 40 m
Sediment Thickness: 50-75 m
Target Drilling Depth: 350 mbsf
Approved Maximum Penetration: Unlimited
Seismic Coverage: SCS with a GI gun acquired on Revelle cruise KIWI02 (August 1997). 3.5 kHz data acquired on Revelle cruise KIWI02. SeaBeam bathymetry acquired on Revelle cruise KIWI02. Hydrosweep bathymetry acquired on the Thompson (September 1999). See Figure 10 for the seismic line and Figure 6 for the trackline.
Objectives: The objectives of Site H2O-4 if selected as the primary observatory site are to
1. Drill a reentry hole into basement for a permanent broadband borehole seismograph at the H2O area;
2. Provide a borehole at the H2O area for other long-term borehole measurements; and
3. Provide a "reference site" with in situ igneous samples in normal, fast-spreading (140 mm/yr full rate), 45- to 50-Ma ocean crust to constrain geochemical and hydrothermal models of crustal evolution.
Drilling Program: Jet-in test. If this becomes the primary observatory site, set a reentry cone with 20 in casing to ~25 mbsf, RCB core from 25 to 325 mbsf, log with the triple-combo and FMS/sonic tool strings, WST for normal-incidence VSP if time permits, open hole and set 16-in casing ~10 m into basement, open hole and set 10-3/4-in casing TD, and log hole with the BHC sonic tool.
Logging and Downhole: Triple-combo, FMS/sonic, WST for normal-incidence VSP, and BHC sonic for cement bond log
Nature of Rock Anticipated: Fractured pillow basalt
Site Summaries continued | Table of Contents