Abstract
Comparing the results of the analysis of microtremor measurement in 1998 and 2013 at Colosseum in Rome, both spectral shapes agree well with each measurement in wide frequency range for all the three directions. However confirming the detail of the predominant frequency and the amplification factor, they slightly differ for each other. The result for 2013 comparing that for 1998 shows that the peak shifts to a little higher in radial direction and lower in circumferential direction, and the amplification factor becomes larger for each direction. The circumferential direction is a direction along the wall and is estimated that the degradation of the structure can be easily appeared not only for the horizontal direction but also vertical direction. And the radial direction may be easy to show the local affection because this direction appears the vending motion strongly. From this perspective, although the predominant frequency for the radial direction becomes larger than that in 1998, the fact that the circumferential direction becomes obviously lower is feared to be noticed. From the mode shown in the animation, the mode changing the phase for 180 degrees between 3F and 4F can be commonly observed in 1998 but not in 2013. It indicates that there is something structural difference between 3F and 4F from 1998 to 2013, and it will be confirmed. Kb value in 2013 becomes almost larger at all the direction than that in 1998. The largest value is shown in radial direction and the value in 2013 becomes 1.4 times larger than that in 1998, and the drift angle of the column at 3F is estimated to reach 1% caused by the earthquake motion of around 100 Gal.
