Wide-angle seismic profiling across an active rifted zone in the middle Izu-Ogasawara arc –KY0511 cruise–

Abstract

We carried out a deep wide-angle seismic experiment using a large airgun array and total 110 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 October 5 to November 3, 2005 (KY05-11 cruise). Objectives of this cruise are to know a velocity structure of the across the northern Izu arc, especially velocity variation between an old Eocene arc beneath the forearc and a new active arc, and a relationship between the structural heterogeneity with the velocity variation and the active backarc rifting. These are important keys to clarify nature of the oceanic arc growth. An airgun-OBS seismic line was set from a trench slope break adjacent to the Izu-Ogasawara trench to the western Shikoku Basin through the forearc basin, the volcanic front, the Sumisu rift, the Miocene rear arc, the eastern Shikoku Basin and the Kinan seamount chain. We shot a large airgun array with total volume 12,000 cu. in. and recorded the seismic signals on OBSs with four components and a 24-channel hydrophone streamer. In this paper, we summarize information of the seismic experiments and introduce OBS data and reflection data.