An installation experiment with broadband ocean bottom seismometers for reducing low frequency seismic noises.

概要

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A seismometer installed on the seafloor is affected by water flow, which could cause a noise in seismic records. The noise is significant especially for low frequencies below 0.1 Hz. For seafloor seismic observatories installed by free fall from a ship, it should be important to improve seafloor coupling of seismometer for reducing the low frequency seismic noise. In order to seek for an installation method that gives a better low frequency performance of seismometers, we conducted an installation experiment using two broadband ocean bottom seismometers with different types of anchor. The two seismometers were placed closely, within 150 m to each other: one with a conventional grid type anchor and the other with a wide planar anchor. The wide planar anchor was used to improve the seafloor coupling of seismometer. The experiment was conducted in the Kumano Basin off Kii Peninsula, from late December, 2007 to early February, 2008. For horizontal components, a noise level obtained from the seismometer with the planar anchor was comparable to that from the seismometer with the conventional anchor. For the vertical-component record, however, the seismometer with the planar anchor had the better noise performance than the seismometer with the conventional anchor at frequencies lower than 0.01Hz.