Ambient vibration measurements to estimate site fundamental periods in Aguadilla and Aguada, PR

Abstract

Considering the high risk of seismic activity of the island of Puerto Rico, this research is aimed at determining the fundamental natural periods of the soil deposits in two areas, downtown Aguadilla and the Espinal neighborhood of Aguada. Also this research studies the influence of massive buildings on the fundamental soil periods. These are the areas of interest not only because of its population and residential areas but also by its proximity to the Mona Canyon. Although it is not currently required in the codes, it is important to know the site soil periods so as to avoid coincidence with the fundamental natural period of the buildings. The study to be performed consists of ambient vibration measurements around the two previously mentioned areas. The data obtained from the ambient vibration measurements where processed by applying the Nakamura procedure also known as the H/V spectral ratio or H/V method to obtain the fundamental periods of the soil deposits. Isoperiod maps where developed in ArcGIS using the data obtained from measurements at the site described before. It was found that the fundamental soil periods vary as the geology of the zone change. In the investigation on the effect of constructions in the soil period it was found that these seem to have a small influence but the results are not very conclusive. Having maps of natural periods of the soil deposits helps to avoid resonant conditions with the structure that can occur in earthquakes of long duration.