Evaluation of site effects based on the 1999 Kocaeli and Düzce earthquake events and seismic microzonation of Gölyaka, Düzce, Turkey

The high seismicity study area situated in a near-fault region in Gölyaka, Düzce, makes the determination of the bedrock geometry more complex, and hence, it makes this area very challenging in terms of a site response study that would aid a seismic hazard assessment. This study developed a basin model to evaluate the site effects in the tectonically controlled and formed Plio-Quaternary fluvial sediments of the Gölyaka region that uniquely falls within the bifurcated near-field fault section of the North Anatolian Fault System (NAFS). Surface seismic surveys and deep vertical electrical sounding (VES), coupled with boring studies, have been performed to determine the presence of the geological heterogeneities and the geometry of the basin over a vast area, and a 3-D basin geometry model was developed. 1D and 2D numerical analyses using an equivalent linear approach were performed to characterize the near-field dynamic soil behavior within the Gölyaka pull-apart basin in the presence of a probable ground motion. The results of the numerical analysis were compared and the performance of the used method was reviewed to ascertain the site effects in the study region. A shear wave velocity of 1100 m/s was accepted as the bedrock depth limit in the region. Based on the VES results, the alluvial thickness in the center of the basin could be much thicker, i.e., almost 450 m. The results of 1D and 2D numerical calculations for soft/weak soils revealed 2D basin effects in spectral accelerations in a 1s period. A three-dimensional effect could also be noticed for the Seis-18 analysis point by comparing the acceleration and velocity spectra along the E-W and NW-SE cross-sections. Based on the recorded weak motion, it was observed that the spectral acceleration showed significant similarity to the results of 1D and 2D analyses. For this particular case, it was deemed that weak motion earthquake was a good indicator of the seismic site effects for the soft and thicker sediments of the study area.


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Citation Formats
K. YOUSEFI BAVIL, “Evaluation of site effects based on the 1999 Kocaeli and Düzce earthquake events and seismic microzonation of Gölyaka, Düzce, Turkey,” Ph.D. - Doctoral Program, Middle East Technical University, 2022.