Wide-angle seismic profiling across the middle Izu-Ogasawara arc for understanding boundary structure between the mature and juvenile arcs - KY0609 cruise -

Abstract

We carried out a deep wide-angle seismic experiment using a large airgun array and total 95 ocean bottom seismographs (OBSs) in the middle Izu-Ogasawara arc area, which was conducted by R/V Kaiyo of Japan Agency for Marine-Earth Science and Technology (JAMSTEC) from August 3, 2006 to September 1, 2006 (UTC) named as KY06-09 cruise. The seismic line runs from the Izu-Ogasawara trench to the eastern foot of the Kinan Seamount Chain in the Shikoku basin through the northern tip of the Ogasawara trough, the volcanic front located off south of the Sofugan and the Miocene Nishi-shichito ridge. Most important objective of this cruise is to construct a velocity structure across this area and clarify commonalities and differences by comparison of velocity structures obtained with previous studies in the whole of Izu-Ogasawara arc regions. The key structures are the continuity of the crustal layers of the Ogasawara ridge and trough, and the current active arc obtained by previous KY05-02 and KY05-11 cruises. And the high velocity lower crust with P-wave velocity of over 7.0 km/s is also one of the key structures because it was discovered at the arc-backarc transition zones in the western Izu-Ogasawara arc and the Mariana arc. The seismic signals propagated from an airgun array with a total capacity of 12,000 cu.in. were recorded by not only OBSs but also a 12-channnel streamer towed from stern. In this paper, we introduce the seismic experiment, especially the schedule and examples of OBS and reflection data.