Abstract
DONET is a network of permanent ocean-bottom seismic stations aimed at improving the detection capability and earlier detection of earthquakes and tsunamis off the Kii Peninsula, where the Tonankai mega-thrust earthquake is anticipated to occur in the near future. DONET consists of 20 stations each of which seismometers and pressure gauges are installed. The orientation of the horizontal components of the seismometer at each station has been measured by using video of a remotely operated vehicle (ROV), which is difficult to measure again for the confirmations. We estimated the seismometer orientations by using the seismic observation data based on three methods; correlation of long-period seismic waveforms with observations on land, direction of P-wave first motion of distant earthquakes, and particle motion of airgun signal. The obtained results are well consistent with each other. The differences between the estimations are at maximum 5 degrees. The difference from the measurement of the ROV video is up to about 10 degrees for most stations, but in some stations the difference is about 50 degrees.
