In this paper, the concrete gravity dam built 40 years ago was partially damaged by the M=7.3 Chi-Chi Earthquake in central Taiwan in 1999. The elastic wave tomography method was applied to identify the safety conditions of the repaired dam in 2010. The resulting velocity profiles showed that the total structure conditions were accepted as a good to questionable condition. The filled materials and cracks existed in some dam components. Seven years later, the updating tracing investigation revealed that the pervious detrimental zones were spatially extended and associated with time. These testing results were also consistent with the findings from the ground penetrating radar inspection.

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