ANALYSIS OF THE OBSERVED LAGGED COHERENCY OF CHLEF CITY (ALGERIA) DEPENDING ON V-s30

Abstract

The assumption that the seismic ground motion imposed on the supports of extended structures is uniform is no longer valid. Especially those which are generally constructed at sites with different soil characteristics. Among the causes which contribute to the non-uniformity of the seismic ground motion is the site effect. However, several coherency models which estimate this spatial variability of seismic ground motion do not consider this effect. In addition, these models have concentrated only on the horizontal direction while neglecting the vertical direction. The work at hand is an analysis of the observed lagged coherency by taking into account the site effect, which is often estimated by the average shear wave velocity over the upper 30 m of depth V-s(30). This analysis tackles the three directions of the seismic ground motion. In this context, this study relies on fifteen seismic events recorded by nine seismological stations located in different sites in Chlef city from December 2014 to October 2015. As expected, the observed lagged coherency decreases with the increase of the separation distance d between two recording stations. The results prove that V-s(30) affects the observed lagged coherency. Thus, the tendency of the observed lagged coherency decreases with the decrease of V-s(30) defined for one or both recording stations. Therefore, the observed lagged coherency is influenced significantly by the site effect. Comparing three components of the observed lagged coherency indicates that the Vertical component is more significant than those of the East-West and North-South components.