A study of seismic microzonation in the provincial center of Aydın (Turkey)

In this study, it was aimed to perform seismic microzonation study for the Efeler District of Aydın province based on the data obtained from the analysis of dynamic soil properties of the investigation field. In this scope, geotechnical data obtained from 144 shallow and 4 deep borings performed recently in the investigation area were compiled. A database containing soil classes in accordance with NEHRP and TBDY-2018 classification systems and average shear wave velocity in upper 30 m (Vs,30) and spectral accelerations and spectral amplification was formed in order to use in the analysis. A probabilistic seismic hazard analysis was carried out by compiling the seismic resources in the region. The response of geotechnical soil profiles to scaled seismic base rock motions was evaluated by using a one-dimensional equivalent linear ground response analysis approach. Estimated soil response spectra obtained from these analyses were calculated according to the criteria in the latest Turkish Building Earthquake Code (2018). The variations in both soil amplification, surface spectral accelerations and ground shake hazard were mapped. A geographic information system-based seismic microzonation map of the investigation field was built up by using the results of the analysis. It was determined that the investigation field composed of only C and D soil classes according to NEHRP soil classification system. The analyses showed that soils of better engineering properties underlay ancient settlements of Aydın city. Advancing from north to south in the investigation area, it was observed that the engineering properties of the soils became worse. A very low percentage of encountered soils were well-graded sand and gravel, the soil profile was predominantly composed of silty sand and silts of low plasticity. Based on the fact that the structure of such soils is prone to liquefaction and the groundwater level in the southern part of the city is high from place to place, it was revealed that it is necessary to make site-specific investigations in field application. Results of analyses show that in Efeler district, evaluation of the soil improvement methods and structural designs as a whole would be an indispensable measure in terms of preparedness to a possible earthquake hazard.