FIGURE CAPTIONSFigure 1. Location of the proposed Site H2O and H2O junction box (large star), proposed Site NU-1A (small star), repeaters along the Hawaii-2 cable (crosses), major fracture zones (FZ), and previous drill sites (circles) from DSDP Legs 5 (Sites 38, 39, 40, and 41) and 18 (Site 172). Mercator map with ETOPO-5 bathymetry.
Figure 2. Hydrosweep bathymetry around the H2O area acquired from the Thompson in September 1999. The site is on a relatively benign ribbon of "normal" oceanic crust. Total relief varies by ~40 m across the region within 2 km of the junction box.
Figure 3. The location of the H2O junction box is shown on the SeaBeam bathymetry acquired during the site survey in August 1997. The locations of the repeaters (AT&T waypoints) on the cable are also shown (filled triangles).
Figure 4. The tracklines during the 1997 site survey cruise on Revelle (KIWI02) are shown with the location of the H2O junction box.
Figure 5. A detail of the track chart shows that the H2O junction box lies between two parallel tracklines southwest of a well-surveyed area.
Figure 6. The locations of the four possible drill sites (Sites H2O-1 through -4) are shown with the tracklines of the 1997 survey. The tracklines are annotated with SCS shot numbers for comparison with the seismic data in Figures 10-13. Circles were drawn at 1-, 2-, and 3-km radius from the junction box. Sites should be beyond a 1-km radius to avoid conflicts with other experiments at the observatory. They should be within a 2-km radius to minimize the effort in running cable to the junction box.
Figure 7. This figure is similar to Figure 6, except the tracklines are annotated with Julian day and time for comparison with the 3.5-kHz data in Figures 8 and 9.
Figure 8. The 3.5-kHz data for the line north of the site shows about 8-10 m of sediment above the first reflector, which we interpret to be a chert layer.
Figure 9. The 3.5-kHz data for the line south of the site shows similar sediment thickness to the north line (Fig. 8).
Figure 10. The unmigrated single-channel seismic (SCS) line north of the site shows relief of about 40 m. Site H2O-1 is at the bottom of a fault block, and Site H2O-4 is at the top.
Figure 11. The migrated SCS line north of the site does not improve the resolution of sediment thickness.
Figure 12. The unmigrated SCS line south of the site shows smooth relief within 2 km of the junction box. Site H2O-3 is at the bottom of a fault block, and Site H2O-2 is in the middle of a block.
Figure 13. The migrated SCS line south of the site does not improve the resolution of sediment thickness.
Figure 14. The Ocean Seismic Network site (OSN-1) is 225 km southwest of Oahu at a water depth of 4407 m. The Hawaii-2 Observatory (H2O) is halfway between Hawaii and California on the retired Hawaii-2 telecommunications cable and is at a water depth of 4970 m.
Figure 15. Vertical component spectra from the seafloor, buried, and borehole installations at OSN-1 are compared with the spectra from the buried installation at H2O and the KIP GSN station on Oahu. H2O has extremely low noise levels above 5 Hz and near the microseism peak from 0.1 to 0.3 Hz. H2O has high noise levels below 50 mHz. Otherwise H2O levels are comparable to the OSN borehole and KIP levels. The sediment resonances at H2O near 1 and 3 Hz are very prominent.
Figure 16. Horizontal component spectra from the seafloor, buried, and borehole installations at OSN-1 are compared with the spectra from the buried installation at H2O and the KIP GSN station on Oahu. The sediment resonance peaks in the band 0.3-8 Hz are up to 35 dB louder than background and far exceed the microseism peak at 0.1-0.3 Hz. That the resonant peaks are considerably higher for horizontal components than for the vertical component is consistent with the notion that these are related to shear wave resonances (or Scholte modes).
Figure 17. Location of Site NU-1A and the debris field for the Nuuanu Landslide. Seismic reflection line 12 from Rees et al. (1993), collected on the 1988 Thomas Washington cruise, shows the stratigraphic relationship of the proximal landslide facies to the distal facies to be cored at Site NU-1A.
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