Summary:  After the July 5th earthquake, we had excess noise, some of which can be explained by charging of the optics possibly by hitting earthquake stops, in particular couplings from the ISI to Darm which could be explained by electrostatic forces between the cage (earthquake stops or image charges in the conductors of the cage), and a 1/f^3 noise which was reduced by discharging.

There is nothing really new in this alog, but things which have not been ploted and posted together.  In all of the plots I am posting here, I have removed jitter as witnessed by the PSL bullseye and the IMC WFS DC signals by selecting the jitter channel with the highest coherence at each frequency, estimating that DARM noise due to jitter at that frequency to be sqrt(coherence)*DARM ASD, and subtracting that in quadrature from the DARM ASD.  This doesn't perfectly get rid of the jitter, which varied between different times in these plots.

The first attached plot shows DARM spectra before and after the EQ, with the additional noise shown in yellow.  Also shown are the noise projections for the new ISI to DARM couplings which were introduced most likely by charging of the EQ stops which happened during the earthquake, which is about an order of too small to explain the amagnitude dditional noise. 

The second plot shows a comparison of the noise before and after discharging (at both end stations), with some lines with different slopes drawn.  Using Rai's charge hopping model (G1401153) you can roughly estimate that the surface charge density removed by discharging both test masses was 4.4e-13 C/cm^2, however, the charge was likely localized and if it came from contacting an EQ stop the EQ stop would also be charged. The coupling from ETMX ISI to DARM was also removed by the discharging, which can explain the noise improvements around 70Hz in this plot.  ITMY was not discharged.

The last plot is meant to show that there is still a lot of noise from 30-60 Hz which was added at the time of the earthquake, which has a slope shallower than the 1/f^3 predicted for charge hopping but cannot be explained by the coupling to ISI motion.