Ocean Drilling Program, United States

We plan to drill one reentry hole at 5 degrees 17.566'N, 110 degrees 4.579'W in the western equatorial Pacific, the location of a future Dynamics of Earth and Ocean Systems (DEOS) multidisciplinary observatory. The drill site is located in 10- to 12-Ma lithosphere of the Pacific plate at a water depth of 3860 m. The hole will be drilled to a total depth of 226 m or more if time permits, which includes 116 m of sediment and at least 100 m of basement penetration. We intend to insert casing to the bottom of the hole and to grout the casing to the basement and sediments. This hole will be used subsequently to install an observatory-quality broadband three-component seismometer (0.001-5 Hz) as well as a high-frequency, three-component seismometer (1-20 Hz) to ensure high-fidelity recording over the range of frequencies normally recorded by the terrestrial Global Seismic Network (GSN). Both seismometers will be digitized with a high dynamic range, 24-bit digitizer. The seismic system, as well as other instrumentation associated with the observatory, will be connected to a DEOS mooring for both power and high-speed data telemetry to a land station and the global Internet. The equatorial site satisfies two scientific objectives of crustal drilling: (1) it is located in one of the high-priority regions for the Ocean Seismic Network (OSN) and DEOS, and (2) it is in oceanic crust created by fast seafloor spreading, providing a rare opportunity to examine crustal genesis, evolution, and crust/mantle interaction for a seafloor-spreading end-member responsible for generating a majority of the oceanic lithosphere. This is a multidisciplinary project that primarily represents the interests of the multiagency DEOS program and the International Ocean Network (ION).