These ringdown measurements, of the LHO QUAD suspensions violin mode 6th and 7th harmonics, were obtained 2 days after the big Earthquake hitting LHO on the 20170706. For this analysis I used 17 hours of detector data in Low noise state from "20170708 06:30:00" UTC. None of the 6th and 7th harmonics were being actively damped or excited. Although clearly the Earthquake excited these harmonics well enough to get very nice ringdowns.
In this analysis, a line tracker (iWave) was applied over each of the identified 6th and 7th harmonic frequencies, locking onto them.
I give next the results for those frequencies that show ringdowns. I also attach 'png' plots which shows; in each column the mode monitored with the top plot being the frequency tracked as a function of time, the middle plot is the 'log(Amplitude)' (natural logarithm of the mode's amplitude). The red dashed lines are respectively the median of the tracked frequency and the fitted first order polynomial to the 'log' of the mode's ringdown. The plot at the bottom shows the Phase deviation respect to the linear fit.
6th Harmonic
Mode frequency (Hz) Q
2836.347 792664427
2837.676 735427842
2839.189 667931233
2841.245 645741246
2842.507 503371109
2843.141 669024332
2843.431 659048452
2844.486 715255321
2846.824 675302066
2847.020 608809212
2848.206 659351953
2849.444 534289274
2849.583 405660077
2850.597 574906401
2853.482 712952420
2853.710 401649469
2857.727 724216344
2858.379 624072692
2864.457 770311177
2866.174 671254082
2868.132 427751583
2878.644 498367912
2878.701 429105364
2880.567 621008999
2880.854 614386214
2882.491 585658907
The 7th harmonic values will be added below in the comments.
