Abstract
For understanding mechanisms of large earthquakes and tsunami, JAMSTEC has been conducting active-source seismic surveys using own seismic system since 1995. The seismic system was mounted on the new R/V Kairei in 1997. In 1999, the seismic system was upgraded for larger volume airgun array (total volume of 197 L), which was mounted on both R/Vs Kairei and Kaiyo. Operation of 100 OBS was also started in 1999. In 2004, the number of section of the streamer cable on the R/V Kairei and OBS were increased for intensive surveys in the Izu-Bonin-Mariana region. The seismic system has provided several important new findings concerning seismogenesis and arc evolutions. However, further improvement of data quality was required for making integrated study of seismic study and material study, which was necessary for the IODP study. To meet the requirements, the new seismic system with a tuned airgun array and a streamer cable with dense group interval have been fit out to R/V Kairei in 2008, and the required capability have been confirmed by field data. Future improvements would be necessary to achieve future scientific requirements.