Damages caused by earthquakes may be considered as the result of the geological characteristics of the sites where they occur. These characteristics are better studied analyzing directly the ground motions due to the earthquakes. This type of studies, however, is limited to the areas that present a high level of seismicity [Nakamura, 1989].
To get out of this limitation, systematic analyses of ambient noise were made, which can be easily performed in areas where the seismicity is low or even absent [Dikmen & Mirzaoglu, 2005].