Daniel Halbe, Josh Smith, Jess McIver

Summary: strong, semi-periodic transient ground motion is propagating up the SEI platforms and down the suspension stages at ETMY. Cause of the ground motion is not yet determined. Effect on the HIFOY signal is not yet evaluated. 

Glitching in the top stage of the ETMY BOSEMs was first identified by Daniel Halbe (see Spectrogram_SUS_Longitundinal_M0_BOSEM_July2.png). These glitches are seen in all DOFs of the suspensions and seismic isolation platforms, have an irregular periodicity of about every 10-20 minutes, a duration of a few minutes, a central frequency of 3-5 Hz, an amplitude in Stage 1 T240s of the ISI on the order of a thousand nm/s (~ um/s) away from baseline noise, and have been occurring since at least June 12, 2013. They are not seen in ITMY suspensions channels. 

For a table that traces these glitches across each DOF and up the stages of seismic isolation to the top stage of the suspension, see: https://wiki.ligo.org/DetChar/HIFOYETMYglitching > Normalized spectrograms (PSD) of the periodic glitches for 1 hour 10 min

Daniel also found them in the lower stage ETMY OSEMs: https://wiki.ligo.org/DetChar/SpectrogramsOfH1AllMassQuadSUSETMY

And Josh Smith traced them to excess ground motion using a representative top stage BOSEM channel (see EMTY_top_stage_BOSEM_pitch_correlation_to_excess_ground_motion.png). 

These glitches have a strong correlation with local ground motion and significant correlation with ground motion near the vault. There appears to be faint correlation with ground motion near MX and the LVEA that merits further investigation.  
(See the normalized spectrogram Top_stage_BOSEM_ETMY_longitudinal_glitching.png and compare to normalized spectrograms Ground_motion_PEM_{location}_spectrogram.png of the same time period)

For additional plots of ground motion at various locations around the ifo during these glitches, see again: https://wiki.ligo.org/DetChar/HIFOYETMYglitching
(If you are unable to see some of the plots on this page, please see the instructions under 'Normalized spectrograms (PSD) of the periodic glitches for 1 hour and 10 min'). 

Note that the reported units of counts are incorrect for all plots (a bug in ligoDV) - these channels are calibrated to nm/s for inertial sensors or to um for BOSEMs and OSEMs.