Figure F1. Schematic representation of a Dynamics of Earth and Ocean Systems (DEOS) observatory.

Figure F2. Location of proposed Site OSN-2 (star) is shown superimposed on a free-air gravity anomaly map derived from Geosat and ERS-1 data (courtesy of David Sandwell and Walter Smith). Other sites shown are the Hawaii-2 Observatory (H2O = diamond), where a hole will be drilled and cased during Leg 200, the OSN-1 observatory, where a hole was drilled and cased during Leg 138, and the notional site (circle) proposed by ION/OSN documents to fill a coverage gap west of the Galapagos Islands. The proposed OSN-2 site replaces the notional site and fills the gap for the region. Additional second priority ION/OSN notional sites lie between Sites H2O and OSN-2. Port calls for the beginning and end of the Leg 203 are in Balboa and San Francisco (squares), respectively.

Figure F3. The proposed drilling site for Leg 203 superimposed on a tectonic map of the world.

Figure F4. Survey trackline (line 9 collected by the JOIDES Resolution during Leg 138) showing the location of the seismic reflection profile in Figure F5. (Modified from figure 18 of Bloomer et al., 1992). Note that the latitudes in the original figure were apparently mislabeled, but have been corrected here. UTC = universal time coordinated.

Figure F5. Seismic reflection profile (line 9 collected by the JOIDES Resolution during Leg 138) through Site 852 where the OSN-2 hole will be drilled. The profile crosses the site twice as shown in the survey trackline (Fig. F4). (Modified from figure 19 of Bloomer et al., 1992). UTC = universal time coordinated.

Figure F6. A. Survey trackline from the Thomas Washington Venture 1 cruise is given in the inset (modified from figure 1 of Mayer et al., 1992). The open circles are stations numbers from the Venture 1 cruise. B. Detailed survey conducted over the Site 852/OSN-2 region during the Venture 1 cruise (modified from figure 3 of Shipboard Scientific Party, 1992b). The location of the seismic reflection profile in Figure F7 is given by the thick red line with positions along the track given in universal time coordinated (UTC).

Figure F7. Seismic reflection profile from the Thomas Washington Venture 1 cruise over Site 852. See Figure F6 for survey trackline. (Modified from figure 4 of Shipboard Scientific Party, 1992b). UTC = universal time coordinated.

Figure F8. Deployment of a borehole seismometer within a cased ODP hole with a reentry cone using a wireline reentry system.

Figure F9. Generalized circulation of the eastern equatorial Pacific showing surface currents (solid arrows), subsurface currents (dashed arrows), California current (CAC), North Equatorial Current (NEC), North Equatorial Countercurrent (NECC), South Equatorial Current (SEC), Peru Current (PC), and Chile Current (CHC). Shaded areas illustrate the general latitudinal extent of the SEC and NEC. Solid circles are the Leg 138 sites, with proposed Site OSN-2 being located at Site 852. EUC = Equatorial Undercurrent. (Modified from figure 1 of Shipboard Scientific Party, 1992a).

Figure F10. A, B. Dynamic sea height from satellite altimetry superimposed upon the wind field for a recent period. The residual shows the different current regimes.

Figure F11. (A) Ekman velocity from satellite scatterometer measurements, (B) geostrophic currents from Topex/Poseidon, and (C) the sum of the currents box superimposed upon sea-surface temperature anomalies (SSTA). The surface currents in the vicinity of proposed Site OSN-2 are ~1 kt. The Equatorial Countercurrent is well to the south.

Figure F12. Sediment thickness along the 110°W transect collected during the Thomas Washington Venture 1 cruise. The locations of the various drill sites shown in Figure F9 are superimposed.

Figure F13. Vertical component spectra from the seafloor, buried, and borehole installations at Site OSN-1 are compared with the spectra from the buried installation at Site H2O and the KIP GSN station on Oahu. Site H2O has extremely low noise levels above 5 Hz and near the microseism peak from 0.1 to 0.3 Hz. Site H2O has high noise levels below 50 mHz. Otherwise, Site H2O levels are comparable to the OSN borehole and KIP (Kipapa, Hawaii) levels. The sediment resonances at Site H2O near 1 and 3 Hz are very prominent.

Figure F14. Horizontal component spectra from the seafloor, buried, and borehole installations at Site OSN-1 are compared with the spectra from the buried installation at Site 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).