Effects of Local Site Conditions on Building Damage in the 2007 Noto-hanto Earthquake

Abstract eng:
The 2007 Noto-hanto earthquake of Mj=6.9 that occurred on March 25, 2007, caused extensive damaged to wooden houses in the affected area, with the most catastrophic damage in the Monzen-machi of Wajima city. The damage to wooden houses appears to concentrate along the foot of alluvial fans in the northern end of the district, suggesting the effects of local soil condition on the damage. In order to clarify the major cause of the damage, field investigations including boring, spectral analysis of surface waves methods were conducted in the district and two-dimensional shear wave velocity profiles were determined. It is shown that the thickness of soft alluvial deposit underlying the district varies from 7-25 m and increases toward the foot of alluvial fans and that the structural damage increases with increasing thickness of the soft alluvial deposit. Dynamic response analyses are conducted with the detected shear wave velocity profiles to estimate ground motions and structural response during the main shock. It is shown that the maximum response of wooden houses, i.e., damage level, in the area could mainly be controlled by strong ground motion with a period of about 1-2 s and that the ground motions in that period range were significantly amplified due to the nonlinear amplification of the thick soft layer underlying the district.

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