HR: 1330h
AN: S52D-0159    [PDF]
TI: Temporal Variation of Ambient Seismic Noise of the Seafloor Borehole Broadband Seismic Observatory WP-1 in the West Philippine Basin
AU: * Shinohara, M
EM: mshino@eri.u-tokyo.ac.jp
AF: ERI, Univ. Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Kanazawa, T
AF: ERI, Univ. Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Araki, E
AF: JAMSTEC, Yokosuka, Kanagawa, 237-0061 Japan
AU: Suyehiro, K
AF: JAMSTEC, Yokosuka, Kanagawa, 237-0061 Japan
AU: Yamada, T
AF: ERI, Univ. Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Mochizuki, K
AF: ERI, Univ. Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Shiobara, H
AF: ERI, Univ. Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Nakahigashi, K
AF: ERI, Univ. Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Mikada, H
AF: JAMSTEC, Yokosuka, Kanagawa, 237-0061 Japan
AU: Fukao, Y
AF: ERI, Univ. Tokyo, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: The seafloor borehole seismological observatory WP-1 is positioned in the west Philippine Basin west of the Kyushu-Palau Ridge. The observatory was installed in April 2001 to fill observational gaps for global seismological networks. The two identical seismometers (Guralp Systems Ltd., CMG-1T) were cemented into the hole as required to assure good coupling. All the necessary power is supplied from lithium batteries. The system has two units of batteries. The data recorder and control unit are placed on the sea floor and a remote operated vehicle (ROV) services the station. We usually operated only one seismometer to reduce the consuming power of the system. The WP-1 observatory was activated in March 2002 using an ROV KAIKO and long-term observation was started using first lithium battery unit. In October 2002, the KAIKO re-visited the WP-1 site and we obtained about six-months continuous data (Mar. 26th, 2002 - Oct. 6th, 2002). The KAIKO visited the WP-1 site again in May 2003 and seven-months continuous data (Oct. 7th, 2002 - May. 7th, 2003) were retrieved. During the third visit, the KAIKO changed an electric connection and the second battery unit started to supply the power to the system. At present, seismic records of 408 days in total have been obtained from the WP-1 observatory. The long-term variations of broadband seismic noise spectra (3mHz - 10 Hz) in the west Philippine Basin were revealed. The noise levels at periods of greater than 10 s are stable all the year round. It is found that the noise levels of the vertical component at the WP-1 reach -180 db (re: 1 m**2/s**4/Hz) at periods between 10 s and 100 s. On the other hand, temporal small variations (maximum fluctuation is 10 dB) of noise levels for periods around a few seconds are seen; the WP-1 station has large noises in summer and fall. The small island (Okinotori-shima) lies about 100 km northeast of the WP-1. The meteorological station is being operated at Okinotori-shima and we can compare the meteorological data at Okinotori-shima and the noise spectrum of the WP-1. The speed of wind looks to be related with the noise levels for periods around a few second.
DE: 3025 Marine seismics (0935)
DE: 3094 Instruments and techniques
DE: 7294 Instruments and techniques
SC: Seismology [S]
MN: 2003 Fall Meeting