Local Site Effects Estimated from Ambient Vibration Measurements at Aqaba City, Jordan

Abstract

Ambient vibration measurements have been employed to estimate empirical site response functions in Aqaba City, Jordan. These measurements were made, using H/V technique, on nine selected sites that are representative for the different geological units beneath the city. The results show site–dependent variations in spectral amplitude, dominant frequency, and amplification level. The dominant frequency of the alluvial sediments shows a general decreasing in the NW direction from 1.8 to 0.3 Hz. No reliable difference in the levels of amplification that are in the range 1.8 to 2.1 was determined. The measurements at the highly fractured granitic site exhibit amplification of 1.8 at 3.9 Hz. The results indicate that the thickness of the loose sediments in western and northwestern part is much thicker than they are in eastern and northeastern parts. The shallow basement rocks in the eastern and northeastern shoulder of the city have direct effect on the measured peak frequency. The intensity and distribution of seismic destruction of the Gulf of Aqaba earthquake (November 22, 1995, Mw = 7.3) appear to correlate well with the dominant frequency as obtained in this study.