Modern strong‐motion accelerometers record instruments’ translational accelerations as well as their rotation. Based on a detailed analysis of the low‐frequency content of acceleration records, Javelaud et al. (2011) removed the permanent tilt information from strong‐motion records. The accuracy of permanent rotation angles derived from acceleration time histories can be checked by comparison with external rotation information. In practice, this can be done at exceptional sites that experience earthquake‐induced permanent rotation and where the permanent rotation is recorded by various instruments.
Situated above a hidden fault and located 4 km from the epicenter during the 2000 MJ 7.3 western Tottori earthquake in Japan, Kasho Dam experienced very strong shaking and a homogeneous tectonic rotation of about 1.5×10−4 rad over the dam and its reservoir areas. Because the dam is well instrumented (plumb line, strong‐motion seismometers, pre‐ and post‐earthquake ground surveys), it makes an ideal site to check the accuracy of tectonic permanent rotation estimated from records of the strong‐motion seismometer located at the dam’s foundation. As a result of this benchmark, the permanent rotation obtained from the analysis of strong‐motion acceleration time histories is consistent with external measurements, which validates the methodology used and that strong‐motion time histories can be used to estimate permanent rotation.