Development of a seismic network over the Pacific islands

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In March 1993, a new station PATS was established on Pacific island, Micronesia, for which we developed a new recording system in a continuous mode. We measured Rayleigh wave group velocities in a period rang 20-150s for the path from Mariana to PATS which is purely the Mariana Basin, and for the path from Solomon island which is purely the Ontong Java Plateau. The Mariana Basin is the oldest seafloor of the Pacific (>16ma) and the Ontong Java Plateau is lava plateau on the seafloor. We got a faster dispersion curve of Rayleigh wave on the Mariana Basin and a lower one on the Ontong Java Plateau. The dispersion curves for the two paths are in marked contrast on the basis of which the shear velocity models were constructed.The Mariana Basin has an at least 120km thick plate with a velocity faster than the standard oceanic model which is the oldest seafloor (160-170ma) in the pacific. Relations between the seafloor age and the surface wave velocity in the Pacific have been studied by Mitchell and Yu (1980), Yoshii (1975). However their studies lack the result for the oldest seafloor because of the poor path coverage over the Mariana Basin. The Ontong Java Plateau has thick crust more than 40km and has thick plate more than 80km.