kiwamu.izumi@LIGO.ORG - posted 16:41, Thursday 20 July 2017 - last comment - 14:26, Friday 21 July 2017(37664)
OMC length and test mass oplevs: unlikely to be culprit for low frequency excess
The attached are comparison of the OMC length and oplev spectra before (4/7/2017 12:30 UTC) and after (today; 20/7/2017 21:00 UTC) the Montana earthquake.
- OMC length signals-- Almost no change. All the lines almost perfectly match up in both frequency and amplitude. There is a subtle change in PZT1_MON where the small bump at 400 Hz shifted to 380 Hz although it is hard to imagine that this is the culprit.
- Oplevs -- No significant change. The noise floor of ITMX YAW between 3 and 30 Hz increased, although this sensor has not been used for the interferometer control. ITMY kept oscillating at 3.25 Hz and the peak height decreased after the earthquake by a factor of several. The sum signal didn't show appreciable changes.
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The attached are the spectra of the BS, PR3 and SR3 oplevs, comparing before and after the earthquake. Again I don't see any suspicious changes except that the BS PIT noise floor improved by a few dB for some reason after the earthquake.
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