Site response of deep alluvial deposits in the northern coast of İzmir Bay (Turkey) and a microzonation study based on geotechnical aspects

• Local site conditions are evaluated.
• Site effects of close and long distance earthquakes are demonstrated and mapped.
• A microzonation model based on geotechnical aspects is developed in an urban area.
• A design spectrum for EDCT is proposed for alluvial site conditions.

İzmir, the third largest city with fast economically growths, in western Turkey, has experienced various moderate-to-large historical and recent earthquakes. Karşıyaka, Çiğli districts and their surrounding areas, located in northern coast of İzmir Bay and one of the major economically and residentially developing districts, are subject to strong shakings due to deep sediments and shallow-soft liquefiable soils in the area. The purpose of this study is to develop a comprehensive microzonation model based on geotechnical aspects and put forth this model for use of residential developments in the area. The properties and dynamic behavior of the Quaternary alluvial soils in the study area were assessed using geotechnical and geophysical data gathered from 461 boreholes and 205 microtremor recordings. One-dimensional dynamic site response analyses were performed with Equivalent-linear Earthquake site Response Analysis (EERA) software by using the simulated earthquake time histories. The maximum ground surface acceleration values obtained from the dynamic analyses were also used for liquefaction potential assessment. Soil classification, dynamic soil properties under different earthquake excitations, spectral amplification, variation of soil predominant period, and liquefaction potential of the study area were evaluated and mapped. The produced maps showed that highest earthquake hazardous soil conditions are located along the shoreline and in the densely populated section of the southwestern part of the study area.