Preliminary Map of Soil's Predominant Periods in Barcelona Using Microtremors

Abstract

 — In order to evaluate soil effects in the urban area of Barcelona, the Nakamura's technique has been used to estimate the predominant periods of soils. Noise measurements for 195 sites were performed using a strong motion accelerograph and a velocimeter. In this work, the resulting preliminary map of predominant periods is presented. The obtained predominant periods are coherent with the geological and geotechnical features of the area. The analysis of the information has allowed the distinctions among several types of soil and underlying materials. A predominant period of about 0.06 s is evaluated for sites located over outcrop Paleozoic rock in the Tibidabo-Collserola Mountains. For sites consisting of material named tricycle, that is the most extensive and also the most heterogeneous zone, predominant period range from 0.10 s up to 2.0 s depending on the thickness of the surface materials and the kind and thickness of the underlying materials. In the Besós river two zones are observed: the riverside with periods between 0.50 s and 0.83 s and a second area with periods between 1.0 and 2.1 s. In the Llobregat river delta the obtained periods are quite homogeneous with values around 0.72 s. Other predominant periods are found in some tertiary rock outcrop.