Origin of artificial noises on broadband seismograms and possible prescription to remove them

Abstract

Artificial noise, which was generated simultaneously as a data storage's hard disc drive started up, has been recorded in STS-1 broadband seismometers' output at two seismic stations where were established over western Pacific Ocean. If this periodical noise is included in the data, it may disturb our analyses of long period ground motions. For this reason, we conducted the experiments under several conditions to find the origin of this noise and to remove it. As a result, the noise wasn't generated by separating a ground line for frame ground from that for power return in the laboratory and the station, which means that the noise was generated by adding some impedance to the ground line for power return. We also propose some ideas to improve the instrument so that this noise may be not generated even if we short the ground line for frame ground and that for power return.