Development and Validation of a 3D Seismic-Velocity Model for the Crust in Eastern Marmara

A 3D crustal model is developed for eastern Marmara, including the city of Istanbul. The model is based on a wide variety of data collected in recent years by different studies, both at crustal and at shallow scale. For modeling the shallow zones, we used mainly data from microzonation surveys carried out by the municipality of Istanbul. The deeper structures are constructed using receiver function and tomographic studies of recent years. All data from various sources are smoothed and put into a unique form having the same number of homogeneous layers at various different locations. A special technique is developed to interpolate the 1D data from irregularly distributed observation points into a volume of a 3D model. We partitioned the complete 3D space by Delaunay triangulation. Within the surface of each triangle, linear interpolation is used to determine the compressional (P) and shear-wave (S) velocities at regularly spaced grid points, which are then extended vertically to fill the space in between. The validity of the 3D model is tested with observed earthquake data (29 September 2004, M-L 4.1) recorded at 86 stations at close distance. Wave propagation in 3D space is simulated using the Wave Propagation Program code (Petersson, 2010). The performance of the 3D model is compared with the 1D models commonly used for this locality. Qualitative and quantitative comparisons clearly show that the 3D model, which includes more details for the shallow structures, fits the observed data better than the 1D model.