Abstract
To understand the surface/subsurface geophysical structure of the Suiyo seamount submarine caldera, which is one of the active Izu-Bonin arc hydrothermal systems, we employed a newly developed acoustic instrument to make detailed imageries of the caldera (sidescan sonar imagery and subbottom reflection profile). To improve the spatial resolution of the seafloor mapping, we chose a deep-tow survey method and developed a new profiling system called the DAIPACK (Deepsea Acoustic Imaging Package). Using this system, we could successfully obtain a high-resolution seafloor imagery (pixel resolution of 1m or better) of the entire hydrothermal area in the Suiyo caldera. We still have difficulty in direct comparison between the imagery obtained and the video/camera images of the seafloor, because of the lack in the navigational accuracy of the ROV system. We have reprocessed the previously interpreted deep-tow seismic reflection data obtained during the KR01-15 cruise in 2001. Applying geometry correction and migration to the data, we could reduce the spatial distortion and the diffraction patterns from the imagery. Both processes made the structural interpretation easier. Interpreting the final cross section, we propose to revise the shallow structure (from the sea bottom to 200 m in depth) of the Suiyo caldera from the previous "layered model" to the "piecewise-continuous block model". We need further discussion on the consistency of our new results to other geophysical observations and models.
