oa Development of hydraulic low frequency marine seismic vibrator

We have fabricated an underwater vibratory seismic source with the scale of 60-70 %, to the real design for towed marine seismic vibrator (MSV) using hydraulic servo system. Several evaluation tests were conducted in the sea using the downsized MSV at a depth of about 250m in water. The performance of the downsized MSV was tested for maximum sound level, frequency characteristic, horizontal directivity, and vertical directivity of the sound field generated from the downsized MSV in Suruga Bay about 100 km away from Tokyo. The sound source level and the frequency characteristic were equal to or higher than the estimated specification between 3Hz and 300Hz. The intensities of the generated sound fields observed at vertical and horizontal directions were equivalent to each other, which indicate that the generated sound field could be regarded almost omnidirectional. A trial seismic survey using a short streamer was also conducted and a shot gather was acquired with several different conditions in sweep frequency bands and in sweep lengths. The results showed that the downsized MSV could perform well to be deployed as a marine seismic source in shallow water surveys and that MSV would be a versatile source as one of alternatives to the existing impulsive seismic sources in practice such as airguns, waterguns, boomers, etc.