An earthquake of 7.4 magnitude in August 1999 caused major loss of life and severe damage within the municipality of Izmit, 170 km southeast of Istanbul (Figure 1). A survey of the damaged buildings was made by the municipal authorities shortly after the earthquake. The municipal government decided to conduct a pilot seismic zonation project to determine whether the cause of the damage was poor construction materials and methods or weak soil conditions. In this project, we investigated the soil conditions with two objectives in mind: (1) to estimate the seismic model of the soil column at each district to determine the geotechnical earthquake engineering parameters, and (2) to map active faults within the municipal area.