As reported in Change of finesse asymmetry during earthquake?? the change in finesse asymmetry happened between two locks separated by an earthquake. In the same moment the OMC temperature changed by about 0.18 degrees. The full fringe can be seen immediately after to be 1.6 degrees. The change corresponds to 0.11 OMC FSR, which can be explained with a master laser frequency relative shift of 2.2e-6 or 450 MHz. Indeed in the same period there has been a reset of master laser thermal correction, which changed by about 2 degrees. According to Benjamin, this might correspond to the predicted frequency change.
Moreover, this change in laser frequency is close to the expected FSR of the reference cavity.
Finally, the change in laser frequency does affect the etalon, since the input mirror acts as a cavity with 10cm length. The frequency shift corresponds to about half a fringe. This seems more or less consistent with the observation.
