Earthquake Ground Motion Simulation Based on Finite Element Method in OJIYA City,JAPAN

Abstract eng:
Strong ground motion simulation based on 2-dimensional finite element method considering topographic effects, local site effects of sedimentary layer and soil-structure interaction has been presented in this paper. The simulation has been carried out for the 2004 Mid Niigata Prefecture Earthquake (MJMA 6.8), in Ojiya city, Japan. The Ojiya General Hospital is located in Ojiya city, the vicinity of the mainshock, which is one of damaged buildings. Input ground motion to this building is required to explain the damages. Strong ground motion records were observed for the mainshock and its aftershocks at a neighboring base-isolation building, Suisen-no-ie. Suisen-no-ie, however, is located at the foot of a hill, while the Ojiya General Hospital is located at the edge of a hilltop. It is likely that input earthquake motions were different between two buildings. Therefore, we have performed microtremor measurements to investigate the structure of surface soft layers. A 2D-FEM model has been constructed, explaining both the peak frequencies of H/V ratios of microtremor observation and Fourier spectral ratios for aftershocks between the Ojiya General Hospital and Suisen-no-ie. Then, we simulated the earthquake ground motion during the mainshock and clarified the topographic effects on both buildings, the different local site effects of surface soft layer and soil-structure interaction. Finally, the structural damages of the buildings have been described from differences in input ground motions.

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