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The objective of the Mariana portion of this leg is to core and to install a CORK at a serpentine mud volcano on the Mariana forearc in the western Pacific. Downhole measurements can be used to determine continuous in situ physical, chemical, and structural properties of the drilled formations. Downhole measurements complement observations and measurements obtained on core and allow core-log integration.

The scientific merits of logging at Site MAF-4B compared to completing the other leg objectives will be reviewed by the co-chief scientists with input from the scientific party prior to implementation of the logging program. The co-chiefs have the final decision and the responsibility to scientifically justify their decision.

Should logging at Site MAF-4B be conducted, it is planned to deploy the triple combination standard toolstring in the pilot hole (A). Physical properties such as natural radioactivity, density, porosity, resistivity, temperature and K, Th, U contents will provide a continuous characterization at high resolution of the drilled formation. The FMS (Formation MicroScanner) provides high resolution microconductance images of mud flows and clast distribution, and is particularly useful for understanding structures and lithostratigraphic variations in the mud flows. The FMS is run with the DSI (Dipole Sonic Imager) to provide sonic measurements.

A long-term seismic observatory will be installed at the West Pacific Geophysical Network site. The logging program is designed to measure physical properties, anisotropy, and hole shape in pilot hole B, objectives that are quite similar to the objectives at the Japan Trench sites drilled during Leg 186. To be effective in locating and evaluating intervals in such holes, logs must be acquired prior to installation of any downhole instrumentation. The laterolog will measure resistivity in basement intervals. Standard geophysical logs can be used to measure physical properties; hole volume can be estimated with high accuracy using the UBI log (acoustic televiewer) in the basement intervals. High-resolution temperature logs should be emphasized to identify permeable zones and in flow/out-flow from both drilling-induced and natural fractures in the holes. (Note: UBI deployment depends on the availability of funds).

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