Various damages to water tanks have been reported due to sloshing and bulging. In particular, bulging has just added to the latest guideline, so it is necessary to understand it as soon as possible. In this paper, we calculate the bulging natural frequencies by the micro-tremor measurement device being installed on the roof panel of the water tank. Furthermore, as they are compared with the results from accelerometers installed on the wall and from finite element analysis, we confirm whether bulging natural frequencies calculated by using this device are correct. We also examine the usefulness of this device. As a result, it is found that calculated bulging natural frequencies by each method were almost identical.
