During Leg 136, a seafloor site was prepared for future experiments to develop the Ocean
Seismograph Network (OSN). Distribution of land-based seismic stations are inadequate to study
the Earth with uniform resolution and the primary objective of ODP was to drill and case a reentry
hole into basement to provide a site for the future emplacement and testing of a broad-band ocean
seismometer, the first site of the OSN. This initial task was completed with the drilling of Hole
843, approximately 225 km southwest of Oahu. The hole was drilled through 242 m of sediment
and 70 m into the basaltic basement. The long-term (5-10 year) goal of the OSN is to establish a
global network of 15 to 20 permanent seismic observatories in the deep ocean. Such a network
would revolutionize studies of global Earth structure, upper mantle dynamics and lithosphere
evolution, earthquake-source mechanisms, oceanic crustal structure, tsunami warning and
monitoring, and deep-ocean-noise sources and propagation mechanisms.
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