During DSDP Leg 5, a series of holes (Sites 39–41) was drilled in the pelagic clay province along longitude 140°W (McManus, Burns, et al., 1970). Site 39 is located north of the Hawaii-2 cable at latitude 32°8.28´N with an age of 60 Ma, and the sediment thickness is only 17 m. Sites 40 and 41 are near the same latitude, at 19°0´N with an age of ~67 Ma. Site 39 is north of the Murray Fracture Zone, and Sites 40 and 41 are south of the Molokai Fracture Zone. The actual "ribbon" of crust on which the cable lies is between the two fracture zones and was not drilled during DSDP Leg 5. Site 40 was drilled in a sediment pond at the base of a large abyssal hill, and drilling was terminated at a chert bed at 156 meters below seafloor (mbsf). The acoustic basement identified as the deepest horizon in the reflection records corresponded to the chert beds. Site 41, located 15 km from Site 40, was considered to be more representative of the sediments in the general area. At this site, basaltic basement was found at 34 mbsf, but there were no cherts. DSDP Leg 18 Site 172 was located between the Murray and Molokai Fracture Zones but east of 140°W in the "disturbed" zone south of Moonless Mountain (Marmmerickx, 1989) (31°2.23´N, 133°2.36´W) at an estimated crustal age of 35 Ma (Kulm, von Huene, et al., 1973). At Site 172, sediment thickness above the basaltic basement was 24 m. The sediment thickness from seismic reflection profiles, however, had been interpreted as 90–105 m. The cause of this discrepancy was attributed to "reverberations in the sedimentary layer and thin sediment cover" (Stephen, Kasahara, Acton, et al., 2003).
During ODP Leg 136 (1991), two sites (Sites 842 and 843) were drilled into the western Hawaiian Arch ~250 km southwest of the island of Oahu (Fig. F2). At theses sites sand layers associated with turbidites from three major Hawaiian landslides were obtained. Quaternary to upper Eocene sediments were recovered to a depth of ~35 mbsf (Dziewonski, Wilkens, Firth, et al., 1992).
In 1998 and 1999, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) cruises (Naka et al., 2000) made bathymetric surveys, dredges, and submersible dives and collected four piston cores targeting the Nuuanu Landslide field and the Wailau Landslides from nearby East Molokai Volcano (Takahashi et al., 2002). The seismic profile along Line 12 (Rees et al., 1993) is shown in Figure F3. Site 1223 is at the northeastern end of Line 12.