We performed a seismic survey using Ocean Bottom Cabled Seismometer (OBCS) system and airguns off the south western coast of Awashima island, Japan, in August 2011 to obtain a seismic velocity structure just below the OBCS system and to estimate orientations of seismic sensors equipped in the OBCS system. The OBCS system was installed in 2010 for a real-time seismic observation, and the system has a total length of 25 km and four seismometers at intervals of 5 km. Based on the seismic velocity structure, we estimated station corrections which are used to adjust travel times due to crustal heterogeneity for the location. We located hypocenters using the seismic data recorded by the OBCSs with the estimated station corrections. Average differences between observed travel times and calculated travel times with the correction decreased. Three component accelerometers are equipped in the OBCS system as seismic sensors. Because horizontal components of seismic waveform data are important in studying waveform analysis, such as source processes of earthquakes and structures by surface waves, it is necessary to estimate accurate orientations of seismic sensors. Therefore orientations of the seismic sensors are estimated using the gravitational acceleration. In addition, we estimated orientations of seismic sensors using particle motions of airgun signals. The orientations of the sensors estimated by different methods show good agreement with each other.

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