Abstract
Ocean Drilling Program Leg 195 consists of a science segment devoted to drilling and casing a hole on the Philippine Sea abyssal seafloor (Site WP-1B) coupled with the installation of a broadband seismometer for a long-term sub-seafloor borehole observatory. The seismic observatory is an important component of the International Ocean Network seismometer net. By filling a large gap in the global station grid, the observatory will help increase the resolution of global tomographic studies, which have revolutionized understanding of mantle dynamics and structure. Moreover, the observatory will allow more precise study of the seismic structure of the crust and upper mantle of the Philippine plate, as well as better resolution of earthquake locations and mechanisms in the northwest Pacific subduction zone.Drilling at Site WP-1B will also provide more precise basement age constraints for models of backarc spreading in the Philippine Sea as well as high-quality sediment sections that may be used to reconstruct the history of microplate motion, climate change, aeolian transport, and arc volcanism in the region.