MICROTREMORS MEASUREMENTS FOR SITE EFFECT INVESTIGATION AT ASWAN NEW CITY, EGYPT Abdel-nasser Mohamed 1) & Raafat Fat-Helbary 1) 1) Aswan Earthquake Research Center, P. O. Box 152 Aswan, Egypt. ABSTRACT: Aswan New City is located about 70 km north to the main active seismic zone in Kalabsha area, where 14 November, 1981 earthquake with magnitude 5.6. was occurred. An accurate estimation of the seismic ground motion across this site is importance for urban development and mitigation of seismic risk. Following many examples of monitored strong earthquakes in the last few years in many countries, show that the local site effects may have a dominant contribution to the intensity of damage and destruction. In this study microtremors survey was carried out at 20 selected sites in the study area. The average H/V spectral ratio indicated that the site amplification ranges from about 1.7 at the central part to 4.6 at the north-western part, while the fundamental frequency ranges from 0.9 Hz at the north-western part to 2.4 Hz along the south eastern part of the study area. Key words: Microtremors, Aswan New City, Fundamental Frequency, H/V Spectral Ratio. 1. INTRODUCTION Site effects associated with local geological conditions constitute an important part of any seismic hazard assessment. Studies of areas affected by damaging earthquakes showed an evident relation between earthquake damage and geological conditions of the site (Sanchez-Sesma et al., 1993; Kagami et al, 1994). Distributions of damage caused by earthquakes indicate that large differences in the extent of damage often occur over relatively short distances; some of the large variations in structural damage can be attributed to local foundation problems, especially when the soil is soft (Aki, 1988; Haile et al., 1997). After the population reached to the maximum capacity around the two banks of the River Nile, in the last decades the Egyptian government planning to construct many new cities North and South Egypt. One of these cities is Aswan New City. Aswan New City is located in South Egypt between latitude 24˚ 09 \ 20 \\ & 24˚ 13 \ 07 \\ N and longitude 32˚ 50 \ 18 \\ & 32˚ 52 \ 08 \\ E, on the west bank of the River Nile about 12 kilometers North to the old Aswan City, where it covers around 21 km 2 as shown in the accompanied locality map (Figure, 1). Aswan New City is located about 70 km North to the main active seismic zone in Kalabsha area, South Egypt, where the epicenter of 14 November, 1981 earthquake with magnitude 5.6. Aswan New City is an urbanization project and it will be good if the assessment of Site Effect being incorporates in the planning stage. Local site response may be evaluated either empirically using seismic recordings or theoretically using synthetics generated record with modeling methods. The theoretical method requires detailed geotechnical information about the materials thought which the seismic waves propagate to the surface. In this study we used an empirical method to determine dominant frequency and amplification factor directly from seismic records at the sites, so the main target of the present study is to estimate the Site Effect (both the amplification characteristics of ground vibration and the fundamental frequency) at Aswan New City site based on microtremors field measurements. This estimation became a major challenge for efficient mitigation of seismic risk.