ABSTRACTWe intend to drill one reentry hole within 2 km of the Hawaii-2 Observatory (H2O) junction box, which is located roughly halfway between California and Hawaii in the eastern Pacific at 27°52.916'N, 141°59.504'W at a water depth of 4979 m (Fig. 1 and Fig. 2). The hole will be drilled to a total depth of about 325 m, which includes ~75 m of sediment and 250 m of basement penetration, and it will be cased to the bottom of the hole. This hole will be used to install a high-quality broadband three-component borehole seismometer (0.001-5.0 Hz, 24-bit digitizing), which can be connected to the Hawaii-2 cable for power supply and continuous real-time telemetry. The H2O site satisfies three scientific objectives of crustal drilling: (1) it is located in one of the high-priority regions for the Ocean Seismic Network; (2) its proximity to the Hawaii-2 cable and H2O junction box makes it a unique site for real-time, continuous monitoring of geophysical and geochemical experiments in the crust; and (3) it is in oceanic crust created by fast seafloor spreading (7 cm/yr half-rate), which represents one end-member for models of crustal generation and evolution and crust/mantle interaction. This is a multidisciplinary project that primarily represents the interests of the Joint Oceanographic Institutions /Incorporated Research Institutions for Seismology Steering Committee for Scientific Use of Submarine Cables, the Ocean Seismic Network group, and the International Ocean Network group. Drilling at the H2O site will also provide useful background information for the Borehole Observatories, Laboratories, and Experiments group and the oceanic lithospheric processes community.
If we gain at least one day of operation time by leaving port early, we plan to double piston core Site NU-1A on the Hawaiian Arch, ~300 km northeast of Honolulu. The upper 100 m of sediment at this site is thought to contain a record of the Nuuanu Landslide, a catastrophic event or series of events that removed ~40% (3000 to 4000 km3) of the Koolau Volcano on the Island of Oahu. We hope to resolve whether the Nuuanu Landslide occurred as a single distinct event or multiple collapses, determine the timing of the landslide, determine the thickness of the landslide deposit at the distal site and groundtruth seismic data to better estimate the volume of the landslide, study the deposition history of the landslide, and gain insight into potential hazards related to giant landslides on the flanks of ocean island volcanoes.
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