Still thinking about earthquakes, I have 2 main points:

1. We can reduce the number of times ISIs trip during earthquakes by reducing the amount of inertial isolation we do a low frequency. Even if we can't lock, changing seismic configurations may save time in recovery.

2. The current earthquake configuration amplifies microseism (.1-.3hz motion) by a factor of a couple. I have some thoughts on improving that, but we need to balance not making things worse at .1-.3 hz (for the summer, we'll need to do better come November) and rolling off the seismometers quickly below .1hz. I've made a Earth_Quake_V2 to address this, but theres more work here to do.

This morning New Zealand had a pretty big earthquake, with peak .03-.1hz blrms velocties around 10 micron/s at LHO.  We noticed this before the velocities reached around 1 micron/s, so I moved the SEI_CONF manager to the Earth_Quake state. Looking at ground and WD trends for the ISI's over the last two months, it seems that normally the BSC ISIs trip at 1-2 micron/s, and today all of the platforms survived. My first plot shows the ITMY .03-.1hz BLRMS, ITMY ST2 WD MON bit and SEI_CONF state (40 is the "windy" state, 17 is the "earthquake" state) for the earthquake today, the second is a plot of an earthquake from Aug 29th. The earthquake on Aug 29th took out all of test mass ISIs (WD_MON goes from 1 to 4), while none of the chambers tripped today, even though the peak velocities were almost 1.5x as high. Kiwamu was even able to run his Guoy phase measurements, without losing the IMC, or any other platforms. He did this with when the .03-.1hz blrms were sitting around 10 micron/s.

Given the fact that we can't lock with 1+ micron/s, I think it would be relatively low risk to automate switching the seismic configuration, for the case where some number of site  seismometers are showing 1 micron/s motion. Maybe we could add this to the SEI_CONF manager.

I really doubt we could get to NLN or even ALS during an eq like this and this may be harder to do when the microseism is high. I think this shows that even if we can't lock the IFO, it might still be worthwhile going to an earthquake robust state to reduce the amount of re-alignment needed to recover, once the earthquake is over.

I've been looking at data from the earthquake on Aug 31, in alog 29403. My third figure is the stock lockloss plot from the first lockloss during that eq. Looking at ALS in the "earthquake" and "windy" seismic configurations on Sheila's plot in 29403, ALS sees more .15ish hz noise in the earthquake state. This is because the current earthquake state turns off the low frequency sensor correction and so the .1-.3hz motion gets amplified by the gain peaking of the 250mhz blends on the ISIs. On the BSCs this gets amplified twice, because both stages use 250mhz blends.

One way  to get around that is to use some narrow band sensor correction to reduce the .1-.3hz motion. I've tried this a bit during the earthquake today, and it seemed like it could have been helping, but things were obviously moving a lot. For now, I've added and "Earth_Quake_V2" state to the SEI_CONF that adds .1-.3 sensor correction to the earthquake state. Commissioners and operators should try using this state the next time we get  a ~.5micron/s earthquake.