Local site characterization and seismic zonation study by utilizing active and passive surface wave methods: A case study for the northern side of Ankara, Turkey

This study encompasses dynamic soil characterization and site classification zonation mapping of the Plio-Quaternary and especially Quaternary alluvial sediments based on the current seismic codes. The study area is located in the Çubuk district and its surrounding area that is situated towards the north of Ankara, the capital of Turkey. The project site is located in a region which has the potential of being seriously affected by probable seismic events occurring along the Çubuk Fault Zone. The Çubuk Fault Zone is thought to be a continuation of the Dodurga Fault Zone and a sub-fault belt of the North Anatolian Fault System that is one of the most prominent fault systems in Turkey with a significant earthquake potential. Sediment characteristics were determined and soil profiles were characterized by surface wave methods at different locations. Non-invasive seismic methods were used to obtain a shear wave velocity profile at 41 sites and two measurements were taken at each site for passive and active surface wave methods. The Multichannel Analysis of Surface Wave Method (MASW) and the Microtremor Array Method (MAM), which gave comparable results, were used as active and passive surface wave methods, respectively. By combining these two techniques, the shear wave velocity profile of the site was obtained. Additionally, the MAM survey alone was implemented at 10 of the sites, especially to get information on the deeper parts of the soil profiles. The geological characteristics of these sedimentary units were compared with the geological and geotechnical boring and seismic site characterization studies to classify the soil deposits. Therefore, the average shear wave velocity results and the variable characteristics of the seismic data along the soil profiles were correlated with these boring studies. This was performed to develop site categories which took site conditions into account according to the design codes of IBC (International Building Code) 2006 and TSC (Turkish Seismic Code) 1998. Consequently, the regional site classification map of the north of the Çubuk basin considering site classes was assessed based on the average shear wave velocity (Vs30) results in IBC 2006 and the shear wave velocity data and thickness of the surface layer based on the Vs values in the TSC.

► Plio-Quaternary sediments of northern Ankara were assessed by surface wave methods.
► Passive (MAM) and active (MASW) surface wave methods gave compatible results.
► Combination of two techniques was utilized to characterize local site conditions.
► The seismic studies were also correlated and complemented by the boring studies.
► IBC 2006 and TSC 1998 based site classification maps were produced and discussed.