corey.gray@LIGO.ORG - posted 14:03, Sunday 25 June 2017 - last comment - 19:46, Sunday 25 June 2017(37116)
Earthquake Report: 6.2 near Tonga, H1 Remained Locked (& mid-shift report)
Summary: H1 Remained Locked, L1 Broke lock, Virgo was already down before EQ
H1 rode through this decent-sized EQ from the South Pacific. The green ITMY Z EQ BLRMS signal approached 1000nm, but never got there (instructions say to take it to LARGE_EQ, which I assume is LARGE_EQ_NOBRSXY [I'm assuming even when locked?], but we never reached the threshold).
Play By Play Of Signals/Tools/Monitors As EQ Approaches/Passes:
- 17:51: Verbal Alarm for "Incoming earthquake"
- 17:51: Seismon estimates ~2min arrival (but didn't see anything.)
- 1st EQ observation (edit: on-site) 17:58: DMT Viewer FOM STS starts & eventually gets to 0.2um at 18:09. Maxes out at 0.9 at 18:30.
- 18:04: Posted on USGS
- 18:06: Posted on Terramon with r-wave arrival estimate of 18:26.
- 18:18: Start seeing signal on Tidal StripTool on wall, AND on ISI_Config medm Strip Tool (ITMy Z EQ blrms almost up to 1000nm at 18:20)
- 18:23 (Scariest part!): DARM spectra shows glitches between 20-80Hz. And also see oscillations on LSC striptool signals. Also seeing on various ASC striptools. Range drops down to 38Mpc.
- 18:35: L1 loses lock due to EQ
- 18:37: Another wave (smaller) appearing on Tidal striptool & ISI_Config.
- 18:55: EQ appears off of H1's radar (still trending down on DMT viewer for STS seismometers). Virgo UP, & L1 still in DOWN state.
The last conversation that I had with Jim left me the understanding that switching to Large EQ anything is done after the lock is broken and is to simply keep the tripping under control. Unless I misunderstood, I don't think switching in-situ is going to help. Am I wrong? anyone?
Ed's right, the only intent of the large eq state is to keep the tables from tripping when the low frequency ground motion is large. Going to this state outside of some narrow circumstances will probably break the lock. The other eq states might work better, but the transition isn't fast enough and will also probably break the lock.
To remind everyone what the response is during an earthquake: While the IFO is locked, do nothing. AFTER the IFO goes down, if the earhtquake is big (probably like a mag 7+, but depends on distance) switch to the large eq state. When .03-.1 hz blrms are somewhere below 1 micron, switch back to the windy state. This is just to prevent tables from tripping, saving time and steps in recovery. The hope is that if the tables don't trip, you're less likely to have to do an initial alignment.
If you like resetting watchdogs and running through initial alignment, feel free to ignore these directions.