Borehole sensor records quake



A permanent, self-contained borehole seismometer placed at 44°N, 160°E in the northwest Pacific on September 11, 1982, recorded the May 26 Japan quake while being serviced by the R/V Kana Keoki. The signal was recorded digitally (100 samples per second) and is undipped. Data are well above noise level from 0.03 Hz to over 40 Hz, a frequency span of more than 10 octaves, on all three orthogonal seismic components (4.5 Hz geophones). The 30 sec signals are shear and surface waves recorded 84 dB below the peak response of the geophones.