Figure 8. 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-1, 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 H1 and H2 could not be determined during installation of the instrument. dB = decibels.