Publications

The vertical cable seismic (VCS) is one of the reflection seismic methods, which uses hydrophone arrays vertically moored from the seafloor to record acoustic waves generated by surface, deep-towed or ocean bottom sources. Analyzing the reflections from the sub-seabed, we could look into the subsurface structure. VCS has the following advantages for hydrothermal deposit survey.  VCS is an efficient high-resolution 3D seismic survey method for a spatially-bounded area.  It achieves high-resolution image because the sensors are closely located to the target.  It avoids the coupling problems between sensor and seabottom that cause serious damage of seismic data quality.  Various types of marine source are applicable with VCS such as sea-surface source (air gun, water gun etc.), deep-towed or ocean bottom sources. Based on the advantages stated above we can apply it not only for shallow oil-gas exploration but for site surveys for drilling, pipeline route surveys or geohazard surveys. Our first experiment of the VCS surveys has been carried out in Lake Biwa, JAPAN in 2009 for a feasibility study. Prestack depth migration is applied to 3D data to obtain good quality 3D depth volume. Based on the results, we have developed four autonomous recording VCS systems. After a trial experiment, we carried out several VCS survey cruises with airgun (GI gun), high frequency deep–towed source and ocean bottom vibrator in actual ocean area around JAPAN. Through the data acquisition, we could confirm that our VCS system works well in the deep water harsh * JGI Inc. environment as well as shallow water. We have, however, also confirmed that the uncertainty in the measured positions of the moving source and the hydrophones in the deep water could lower the quality of subsurface image. We are continuing to develop a total survey system that assures an accurate positioning and deployment techniques.