Summary: I calculated the pitch of the mirror after the earthquake using geometrical considerations: 13.4 mrad. In an analogous way, I did the same using data from OSEMs V2 and V3: 9.5 mrad and 8.8 mrad respectively. The values are different, but to a certain extent consistent.

Using Hirata-san's picture posted in the klog 18330, and Kamiizumi-san's CAD drawing of the PCB board, it was determined that the position of the oplev beam spot with respect to the centre of the QPD was:

• Horizontal: 1.5 mm
• Vertical: 17.3 mm

From Yokozawa-san's drawings we also know that the distance from the mirror to the tilt QPD is 1050 mm, with the angle of incidence on the mirror 52 degrees.  This means that the effective lever arm length is 0.646 m. In turn, this implies that the pitch of the mirror is ( 17.3 mm / 0.646m ) / 2 = 13.4 mrad.

The pitch of the mirror was 13.4 mrad from the direction defined by the centre of the QPD

Using OSEMs V2 and V3, we can estimate by how much we moved the IM when we recovered the pitch alignment. This should be similar to the pitch displacement just calculated.  OSEM V1 ended up in out of range after recovery, so I didn't use it for this calculation. Along the longitudinal direction, OSEMs V2 and V3 are 48 mm from the suspension rod. The measured displacement of each OSEM and the pitch associated to such displacement are

• V2: -456 um, 9.5 mrad.
• V3: -423 um, 8.8 mrad.

Although the values calculated using the oplev are all different, they are consistent in the sense that they indicate a very large displacement.