Terramon told us that we had an incoming earthquake large enough to likely break lock, so I asked Jim to take us out of Observing mode so that I could quickly try to increase the SRM offloading, to see if that would save the lock. In the end, we still lost the lock.
I changed the SRM M1 Lock L gain from the nominal -0.02 to -0.05 with a 10 second ramp.
I need to look at the data to know more, but the verbal alarm did not complain about SRM saturations. It did however complain about ETMY saturations.
If that really did help prevent SRM saturations from causing our lockloss, I wonder if we should think about increasing every optics' offloading gain by a factor of 2 or 3 when we have an earthquake coming. Anyhow, I need to look at the data to see what really happened, and to see if I can figure out what really helped.
SRM offloading by just increasing the gain was no good.
I think that I must have made the crossover unstable, which made something not good at the AS port. The HARD ASC loops (particularly DHARD Pitch) start to oscillate, which is probably why all 4 test masses are saturating their L2 drives at the time of lockloss (and ETMY is also saturating the L3 drive).
So, oopsies. While trying to save the lock, I seem to have killed the lock.
To actually fix the SRM offloading, I'll need to measure the crossover to check its stability, and maybe tune the filters a bit.