Figure CaptionsFigure 1. A. Location map of seismic station coverage in the northwest Pacific. Stations needed in the oceans worldwide. At least five major plates with consuming boundaries interact in the northwest Pacific, causing subduction, back-arc opening, slab collisions, terrane accretion, and island arc development. Solid circles indicate land seismic stations, whereas open circles are current and proposed seafloor borehole observatories. Note that a few borehole stations effectively complement and expand the existing network. YSS = Yuzhno Sakhalinsk, Russia, 46.9583°N, 142.7610°E; NMR = Nemuro, Japan, 36.1525°N, 145.7430°E; PHN = Pohang, Korea, 36.03°N, 129.36°E; HCH = Hachijo-shima, Japan, Reserved; OGS = Chichi-jima, Japan, 27.0570°N, 142.2030°; MCSJ = Minami-tori-shima, Japan, 24.290°N, 153.978°E; ISG = Ishigaki, Japan, 24.3793°N, 124.2347°E; PATS = Ponsei, Micronesia, 6.8367°N, 158.3125°E; PMG = Port Moresby, Papua New Guinea, -9.41°N, 147.16°E; TGY = Tagaytay, Philippines, 14.10°N, 120.94°E. B. Location of proposed Site WP-1B in relation to global seismicity. M = magnitude.
Figure 2. Location map showing Deep Sea Drilling Project Sites 290, 294, 295, and 447 and proposed Site WP-1B in the Philippine Sea.
Figure 3. Photograph of the Japan Marine Science and Technology Center's (JAMSTEC) ROV, the Kaiko. All seafloor assembly electrical connections, the data storage unit, and the data handling and control unit (see Fig. 5A and 5B) can be removed and replaced by such an ROV. The Kaiko will visit Site WP-1B to activate the borehole observatory after Leg 195.
Figure 4. Noise spectra from the borehole seismometer at Site JT-1 (Leg 186) off Sanriku, Japan (from Suyehiro et al., 1999). The noise level is positioned at a satisfactory level between the high noise model and the low-noise model. The rise of noise around 0.01 Hz is known to be infragravity wave noise induced from a long-period surface wave in the ocean. At Site WP-2, the borehole seismometer will be installed in the basement so that such serious noise should be sufficiently suppressed. The seismometer in Hole 1150D (proposed Site JT-1C; Leg 186) has a vertical (V) and two horizontal components that are perpendicular to each other. The direction of the horizontal components could not be determined during installation of the instrument; therefore, H1 and H2 denote the noise spectra from records of two horizontal components of the seismometer. dB = decibels.
Figure 5A. Schematic block diagram of the seismic observatory components.
Figure 5B. Schematic configurations of the instrument package for broadband seismometry. All the equipment in this assembly is accessible to an ROV. Cables from the sensors grouted at ~500 mbsf terminate in a four-way underwater-mateable connector block. The data control unit (MEG) plugs into this connector block. A single output from the top of this package is coupled (by ROV) to the battery/recorder unit (PAT) installed after the sensors are grouted. A data recording unit (SAM) can be retrieved by an ROV when required. MEG = multiple-access expandable gateway. PAT = Power supply access terminal. SAM = storage acquistion module.
Figure 6. Schematic of the seafloor assembly with expected lithologies extrapolated from Leg
185. PAT = Power supply access terminal.
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