An-Najah Staff

The city of Nablus is located in one of the highest seismic hazard areas in Palestine, and many buildings were completely destroyed in the city during the historical earthquakes. The population of Nablus city is rapidly increasing and new urbanizing areas are growing to the eastern and western parts where they are located at soft sediments. Consequently, the evaluation of surface soil effects is very important from a standpoint of earthquake disaster mitigation. A landform classification geotechnical map was modified by analyzing available boreholes logs and seismic refraction data. Microtremor measurements were carried out at about 16 sites in the study area and Nakamura’s method (1989) was applied for determining predominant periods. The results showed that predominant period, determined at rock site in different locations of the city, is about 0.55 sec whereas at soft soil sites, in the center of the city, the predominant period reaches more than 1.0 sec. At medium soil sites, mainly in the western part of the city, the predominant period ranges between 0.65- 0.75 sec. The obvious difference of the predominant periods between hard rocks and soft soil sites reflects the surface soil cover and it coincides with the variations of geological outcrops. Three main surface soil units, which have different site effects, were figured out from this study. Keywords: microtremors, soil effects, Nakamura’s method, seismic microzoning.