[Shuta Tanaka, Ide, Obayashi (Aogaku), Yuzurihara]
We performed the lockloss investigation for the lockloss which happened between 2025/07/02~07/08. The previous lockloss investigation was posted in klog34685. During this period, there were 35 lockloss from the OBSERVATION state. The plots are listed in DAC wiki.

Quick saturation of OMC DCPD

There waa no lockloss with the quick saturation.

Slowly saturation of OMC DCPD

For 10 lockloss (i=70, 74, 76, 77, 80, 83, 84, 90, 91, 103), 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 15 lockloss, the EQ label was asgned.
The most of earthquakes seems to have occurred near the Tokara Islands. 42%(=15/35) of lockloss was caused by the earthquake.

Excess of 1~10Hz seismic motion

For 2 lockloss (I=97, 98), 1Hz label was assigned. In addition, for 3 lockloss (I=75, 82, 85), we found the excess of the 1Hz seismic motion.

Alignment upward the AS port

For 3 lockloss (i=81, 94, 102), 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 1~3.

For 1 lockloss (i=99), the gradual drop of IR trans power was observed, as shown in Figure 4.  We are still not sure why the gradual drops happened.
Comments from experts are very helpful.

Lockloss by the human request

For 1 lockloss, the REQ label was asigned.