Directionally Effect Observation in Topographical Site-Effects at Feden-Sema Range (Guelma-Northern Algeria) from Ambient Vibration

Abstract

The Eocene Feden-Sema Range is a topographical structure located in the complex area of Mechtat El-Ababsia (Guelma) characterized by topographical site effects from an experimental investigation using earthquake and ambient vibration. The structure has its maximum orientation toward the south and a half-circular shape. To study the directionality effects caused by this structure, two profiles of ambient vibration measurements were carried out on the maximum axe and through the range of 12 points. The analysis of the horizontal over vertical spectral ratio indicated that the fundamental frequency, f0, of the topographical structure is constant and around 3.0 Hz in all measurement points. The ambient vibration analysis in the 0.1–20 Hz frequency domain showed that f0 is strongly related to the polarization or directionality, where the maximum amplification is obtained at 45° azimuth from the north with an amplitude of 3.5 times compared to 0° at 2.5 times. The obtained result is of great importance in showing that the topographical site effects are not free from the directionality influence in the ground motion, which must be taken into consideration in the case of building construction orientation.