Liquefaction Potential and Vs30 Structure in the Middle-Chelif Basin, Northwestern Algeria, by Ambient Vibration Data Inversion

Abstract

The Middle-Chelif basin, in northwestern Algeria, is located in a seismically active region. In its western part lies the El-Asnam fault, a thrust fault responsible for several strong earthquakes. The most important being the El-Asnam earthquake (Ms = 7.3) of 1980. In the present study, ambient vibration data with single-station and array techniques were used to investigate the dynamic properties of the ground and to estimate the Vs30 structure in the main cities of the basin. Soil resonance frequencies vary from 1.2 to 8.3 Hz with a maximum amplitude of 8.7 in. Collapsing behavior has also been demonstrated west of the city of El-Attaf, reflecting a strong potential for liquefaction. A Vs30 variation map and a soil classification for each city were obtained mainly by inversion of the HVSR and Rayleigh wave dispersion curves. Finally, an empirical prediction law of Vs30 for the Middle-Chelif basin was proposed.