South and SouthEast of Spain are the regions with a higher seismic hazard in Spain Consequently, all the municipalities in Alicante province has to develop seismic emergency planning. Besides, the south of Alicante province and, in particular, the cities of Elche and Alicante are located in a sedimentary deposit, which can reach hundreds of meters, so site effects can be important. Additionally, most of the building stock belongs to periods without seismic normative, increasing, therefore, their vulnerability. Furthermore, following the damage caused by earthquakes in Spain, it has been observed that there are significant differences in the spatial distribution of damage from site to site in buildings with similar seismic behavior, located in a similar site. Hence, many authors have stated that the main factor responsible for the different damage distribution could be the building height. The seismic response of a building depends on its dynamic characteristics (fundamental period, T, damping ratio, ξ, and modal shape) and on the input ground motion. Among the existing methods to determine the T and ξ parameters, the best ones probably are to record weak earthquakes (or near explosions) or induced vibrations inside the building. However, both techniques need a very expensive and time-consuming effort when it is applied to a large number of buildings. A possible alternative is the measurement of ambient vibrations. In this work, ambient vibration measurements were performed at the geometrical center of the plan on the top floor of buildings with different height and year of construction in the municipality of Alicante and Elche (both in the Alicante province), assuming that this point coincides with the mass center of the floor. The preliminary results follow a linear relationship between the number of stories and the fundamental period. Finally, the results have been used to estimate the probability of resonance in several districts of both municipalities.

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