[Shuta Tanaka, Ide, Obayashi (Aogaku), Yuzurihara]
We performed the lockloss investigation for the lockloss which happened between 2025/07/09~07/15. The previous lockloss investigation was posted in klog34686. During this period, there were 27 lockloss from the OBSERVATION state. The plots are listed in DAC wiki.

Quick saturation of OMC DCPD

For 4 lockloss (i=112, 114, 115, 118), the quick saturation of OMC DCPD happened. This phenomena looks similar with the lockloss reported in klog34527. Compared with the usual saturation of OMC DCPD, the quickness (or the time scale) of the saturation is different. One of them have the ISC_WC_L label.
Although we checked the other channels, we didn't find the coincidence change. If you find the coincidence with other channel, that's helpful to understand the cause behind the lockloss.

Slowly saturation of OMC DCPD

For 7 lockloss (i=110, 113, 124, 125, 126, 127, 129), the slowly saturation of OMC DCPD can be seen. This phenomena is same as regular report one. The oscillation just before the saturation was 20~40 Hz. One of them have the ISC_WC_L label.

There was no lockloss with 18 Hz oscillation.

Earthquake

For 8 lockloss, the EQ label was asgned. During this period, many earthquakes occurred near the Tokara Islands.

Excess of 1~10Hz seismic motion

For 6 lockloss (i=108, 109, 111, 119, 121, 123, 131)(4 of them has also EQ label), 1Hz label was assigned. In addition, for 1 lockloss (i=108), we found the excess of the 1Hz seismic motion.

Alignment upward the AS port

For 3 lockloss (i=105, 107, 120, 130), we can see the increase of OMMT2 TRANS, increase of AS17, the large feedback for ASC DHARD. the gradual drop of IR trans. I guess the alignment upwad the AS port (before the OMC) was changed before the lockloss, as shown in Figures 1~4.

Lockloss by the human request

For 2 lockloss, the REQ label was asigned.