Leg 203Equatorial Pacific IonA single site will be drilled in the equatorial Pacific to establish a borehole that will serve as a site for a future International Ocean Network (ION) and Ocean Seismic Network (OSN) observatory. The site (5°17.57'N, 110°4.58'W), which will be located in ~10-12 m.y. old lithosphere of Pacific Plate, was chosen to fill a large gap in seismic coverage in the region between Central America and the Pacific Islands. During Leg 203, the site will first be cored and then a second hole will be drilled, have a reentry cone set, and be cased into basement. The boreholes will penetrate through about 120 m of sediment and extend into the basement by about 100-150 m. Installation of the borehole instruments will be done using wireline reentry after Leg 203 has ended. Instrumentation will include a broadband triaxial borehole seismometer and a triaxial high-frequency seismometer, both of which will reside in basement portion of the borehole, and a broadband hydrophone, which will be suspended in the water column near the SOFAR channel. The observatory will be attached to a buoy that will provide power, data storage, and satellite communication capabilities, making it possible to return data daily to established data centers. The observatory will be part of a global network that will resolve mantle and core structure, particularly anisotropy and lateral heterogeneities that may exist in these regions, and will aid in mapping the core-mantle boundary, a region that is probably the birth place of hotspots and the resting place of subducted slabs. The observatory will also improve the detection threshold for earthquakes occurring in the region. A secondary goal will be to recover and characterize the physical properties and geochemistry of an igneous basement section that was formed by super fast seafloor spreading (141 mm/yr full spreading rate).
Staff Scientist: Tom Davies Operations Schedule | Back to FY 01-02 Abstracts
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