INSTABILITY OF THE STS SEISMOGRAPH AT SYOWA STATION, ANTARCTICA

• Main Authors: ヤマモト マサト, Masato YAMAMOTO
• Format: Report
• Language: English
• Published: ABSTRACT 1993
• Subjects: Syowa Station; Antarc*; Antarctica
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=2725; http://id.nii.ac.jp/1291/00002725/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2725&item_no=1&attribute_id=18&file_no=1

Seismic observations by a three-component STS (Streckeisen Seismometer) seismograph were started at Syowa Station (69°S, 39°E) in 1989. The seismographs have been installed in the thermal insulation boxes since 1990. Broad-band (BRB) and long-period (LP) seismic signals were recorded on both cassette magnetic tape and long-term chart recorders for monitering. The recording has been contaminated by shift-noise and baseline shift. The shift-noise is a kind of pulse-like noise which appears on the monitoring record of the (mostly) vertical component. The baseline-shift is an instrumental drift that causes the recording instrument to deviate from the baseline center on the monitoring seismograms. In March 1991,a thermometer was installed in the thermal insulation box of the vertical component for making clear the cause of noises. There was a seasonal change in temperature in the box, ranging from 8℃ to as low as-7℃. A total of 591 shift-noises was observed on the seismogram of the vertical component in 1991. During a time when shift-noises occurred more than ten times in a day, the temperature in the thermal insulation box fell suddenly, by 2-3℃, within a few days. At the same time, the daily mean air temperature decreased 10℃ in a day. The shift-noise on the seismograms of the horizontal components were recorded only several times during one year. The occurrence of baseline-shift of the vertical and N-S components were also correlated with temperature change in the thermal insulation box. However, there were no baseline-shifts recorded on the E-W component seismogram through the year. We concluded from the STS seismic observation in 1991 that noise on the STS seismograms has a significant correlation with the temperature change in the thermal insulation box. We plan to use heaters in the thermal insulation box, to keep the temperature constant.