I performed the lockloss investigation for the recent lockloss from the OBSERVATION state of the LSC_LOCK guardian, between 2025-06-04 06:24:36.937500 UTC and 2025-06-05 00:44:39.437500 UTC. The previous lockloss investigation was posted in klog34054. During this period, there were 6 lockloss from the OBSERVATION state. The plots are listed in DAC wiki.

1~10Hz seismic motion made the IMC lockloss

For 2 lockloss, we saw the excess of the seismic motion with 1~10 Hz, which made the oscillation of the IMC length control and caused the IMC lockloss.

• 2025-06-04 10:35:49.562500 UTC
• 2025-06-05 00:44:39.437500 UTC

From my experience, their cause seems to be blasting. I will wait for the report on the actual blasting execution time.

Long-term stability of alignment

Thanks to the modification of the BPC for ETMY pitch (klog34016) on June 2, the lock duration is now longer and more stable. I focused on the drift of the alignment control, such as ASC or BPC.

Figure 1 shows the BPC error and feedback signals. It takes 2 hours to reach an equilibrium of BPC for PRM YAW. It takes 30 minutes to reach an equilibrium of BPC for ITMX YAW. Figure 2 shows the oplev signals. The amount of shifting the PRM seems ~2 urad.
Except for this, I didn't see a significant drift of the alignment control (ASC and BPC).

Oscillation of ASC control

Figure 3 shows the oscillation of IR trans and DHARD_P at -1 min. Coincidentally, we can see the excess of OMMT2 TRANS. This oscillation can be seen in other ASC and BPC (Figures 4 and 5).

Memo

Figure 6 shows the duty cycle on June 3 and June 4. They were 76% and 71%, respectively.