Near Field Effects of Hidden Seismic Faulting on a Concrete Dam

概要

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The 2000 Western Tottori earthquake (M_J 7.3), Japan, was caused by a hidden seismic fault underlying the Kasho Dam, a 46 m-high concrete gravity dam. Strong-motion accelerometers registered peak accelerations of 2051 at the top of the dam and 531 gal in the lower inspection gallery. Integration of the acceleration records in the gallery showed a permanent displacement of 28 cm to the north, 7 cm to the west, and an uplift of 5 cm. The dam survived the earthquake without serious damage, but the reservoir water level dropped suddenly by 6 cm followed by damped free vibration that continued for several hours. Based on numerical simulation and field observations, the water level change is attributed to ground displacement in the near field and subsequent seiching of the reservoir. The vibration period of the dam in the upstream-downstream direction changed noticeably during the main shock, probably due to hydrodynamic pressure variation. The earthquake caused cracking of concrete floor beams in a sub-gate control room, which was repaired by post-tensioning with steel bars. Micro-tremor measurements were used to evaluate the effectiveness of the repair work.
日本自然災害学会の論文