Analysis of Vibration Characteristics based on Microtremor Measurement of Hikone Castle and Surrounding Ground

Abstract

In this research, in order to obtain the basic data while evaluating the earthquake safety of the Japanese National Treasure: Hikone Castle, we conducted microtremor measurement inside the Tenshu (castle tower), Tsuke Yagura (attached turret) and Tamon Yagura (hall turret) as well as on the surrounding ground. Consequently, by analyzing the result of microtremor measurement conducted inside the buildings, we clarified the natural frequencies of Tenshu, Tsuke Yagura and Tamon Yagura and the mutual coupling effect of each other’s vibration characteristics. Next, from the result of the microtremor measurement conducted on the surrounding ground, we generally clarified the thickness of the surface layer ground of Nishinomaru (west ground) and Honmaru (main ground where Tenshu was constructed), as well as the natural shape of the ground. Meanwhile, we also found except the fact that difference of H/V spectral ratio due to direction can only be verified on the foundations close to Ishigaki (stone wall); on the ground a few meters away from Ishigaki, outstanding frequencies of the surface layer ground as well as outstanding frequencies of the ground around Ishigaki can be observed.