4 th International Conference on Earthquake Geotechnical Engineering June 25-28, 2007 Paper No1631 APPLICATIONS OF ENGINEERING SEISMOLOGY FOR SITE CHARACTERIZATION Öz YILMAZ 1 , Murat ESER 2 , Mehmet BERILGEN 3 ABSTRACT We determined the seismic model of the soil column within a residential project site in Istanbul, Turkey. Specifically, we conducted refraction seismic survey at 20 locations using a receiver spread with 48 4.5-Hz vertical geophones at 2-m intervals. We applied nonlinear tomography to first-arrival times to estimate the P-wave velocity-depth profiles and performed Rayleigh-wave inversion to estimate the S-wave velocity-depth profiles down to a depth of 30 m at each of the locations. We then combined the seismic velocities with the geotechnical borehole information regarding the lithology of the soil column and determined the site-specific geotechnical earthquake engineering parameters for the site. Specifically, we computed the maximum soil amplification ratio, maximum surface-bedrock acceleration ratio, depth interval of significant acceleration, maximum soil-rock response ratio, and design spectrum periods TA-TB. We conducted reflection seismic survey along five line traverses with lengths between 150-300 m and delineated landslide failure surfaces within the site. We recorded shot gathers at 2-m intervals along each of the the seismic line traverses using a receiver spread with 48 40-Hz vertical geophones at 2-m intervals. We applied nonlinear tomography to first-arrival times to estimate a P-wave velocity-depth model and analyzed the reflected waves to obtain a seismic image of the deep near-surface along each of the line traverses. Keywords: Engineering Seismology, Travel Tomography, Surface-Wave Inversion, Reflected Waves INTRODUCTION A geotechnical project involves interdisciplinary coordination between the seismologist, geomorphologist, and the geotechnical and earthquake engineers. We obtain a seismic image of the near-surface from the analysis of reflected waves to delineate fault geometry and geometry of layers within the soil column. We obtain a P-wave velocity-depth model of the soil column from the analysis of refracted waves. Finally, we estimate an S-wave velocity-depth profile for the soil column from the analysis of surface waves. These intermediate products, combined with the geomorphology of the site and the geotechnical borehole and laboratory data, are then used to define the parameters for the soil geometry, soil pedology, and the soil dynamics associated with the geotechnical model of the soil column, which is then used for geotechnical design for soil remediation. Figure 1 shows the location map of the site. The size of the area is approximately 40 acres. Elevations vary between 125-180 m. Topography is fairly flat in the western half of the site while there is a downhill slope in the northerly direction in the eastern half. The top soil is entirely clay. 1 Director, Anatolian Geophysical, Istanbul, Email: oz@anatoliangeo.com 2 Operations VP, Anatolian Geophysical, Istanbul, Email: murat@anatoliangeo.com 3 Assoc. Professor, Department of Civil Engineering, Yildiz technical University, Istanbul, Email: berilgen@yildiz.edu.tr