Improvement of seismic observation in the ocean by use of seafloor boreholes

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doi: 10.1785/0120020088
Author(s): Araki, Eiichiro; Shinohara, Masanao; Sacks, Selwyn; Linde, Alan; Kanazawa, Toshihiko; Shiobara, Hajime; Mikada, Hitoshi; Suyehiro, Kiyoshi
Author Affiliation(s): Primary:
Carnegie Institution of Washington, Department of Terrestrial Magnetism, Washington, DC, United States
University of Tokyo, Japan
Japan Marine Science and Technology, Japan
Volume Title: Bulletin of the Seismological Society of America
Source: Bulletin of the Seismological Society of America, 94(2), p.678-690. Publisher: Seismological Society of America, Berkeley, CA, United States. ISSN: 0037-1106 CODEN: BSSAAP
Note: In English. 34 refs.; illus., incl. 1 table
Summary: We developed a long-term, high-quality seismic ocean floor borehole observatory system, the "Neath Seafloor Equipment for Recording Earth's Internal Deformation (NEREID). Four NEREID borehole observatories were installed in the Japan Trench off-Sanriku area (JT1, JT2), in the northwestern Pacific Basin (WP2), and in the Philippine Sea (WP1). The borehole sensors are cemented in the borehole to assure good coupling of sensors to the ground as well as to avoid effects of water flow around the sensors, which may have been a problem in previous borehole installations. The NEREID seismic records from two of the observatories (JT1, WP2) were free from long-period noise due to turbulence in the seafloor boundary current or to water flowing around the sensor that is significant on the seafloor. The infragravity wave noise clearly observed around 0.01 Hz on the horizontal components was significantly higher in the JT1 seismometer in the sediment because of the low shear modulus of the sediment. Ocean waves of long wavelength cause the infragravity wave noise. It is thus necessary to install seismometers in boreholes below the sediments to reduce the infragravity wave noise.
Year of Publication: 2004
Research Program: ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; 20 Geophysics, Applied; Boreholes; Crust; Depth; Geophysical methods; Instruments; Leg 191; Mantle; Marine methods; Noise; Observations; Ocean Drilling Program; Ocean floors; Seismic methods; Seismic networks; Seismicity
Coordinates: N120000 N420000 E1600000 E1430000
Record ID: 2004057689
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