Non-Stability and Non-Reproducibility of Ambient Vibration HVSR Peaks in Algiers (Algeria)

ABSTRACT

The ambient vibration horizontal-to-vertical spectrum method (HVSR) is widely used in microzonation and structural studies, assuming stability and reproducibility of HVSR frequency peaks. A 35-day continuous HVSR monitoring performed in the suburbs of Algiers (Algeria) reveals that HVSR peaks are not always stable and reproducible both in frequency and amplitude. HVSR curves show a first peak, which varies from 0.9 to 1.8 Hz with amplitudes from 0.9 to 3.3, and a second peak from 5 to 7.7 Hz with amplitudes from 1.4 to 4. These results show that HVSR peak frequencies and amplitudes are highly sensitive to nearby anthropogenic sources.

KEYWORDS:

• Ambient Vibrations
• Frequency Peak Instability
• Site Effects
• Soil Structure
• Microzonation

Acknowledgments

HVSR data used in this study have been acquired by the authors and colleagues from the Centre National de Recherche Appliquée en Génie Parasismique, Algiers, Algeria (CGS), using equipment from IRD-ISTerre, Grenoble, France, and are available from the first author. Borehole data are taken from a 2009 unpublished geophysical investigation report made available by the Laboratoire Central des Travaux Publics (LCTP) from Algiers. We thank two anonymous reviewers for very constructive remarks that helped improve the manuscript. The authors are thankful to all the colleagues from the Centre National de Recherche Appliquée en Génie Parasismique, Algiers, Algeria (CGS) who participated in the data acquisition. The authors are thankful also to all the people working on the Baraki stadium construction who kindly spent some of their time in useful discussions.