Estimation of Ground Motion at One of the Damaged Building Sites Following the October 30, 2020, Samos Earthquake

On October 30, 2020, an earthquake with a moment magnitude of 7.0 occurred on the Kaystrious fault in the north of Samos Island. Although the effects of the earthquake in İzmir were widespread in several districts, the majority of the damage was concentrated in alluvial sites, the Bayraklı-Manavkuyu region, which is approximately 70 km away from the epicenter being the most heavily affected area. The fact that none of the buildings as high as four storeys did not experience considerable damage in contrast with the heavily damaged or collapsed structures with a number of storeys varying between 8 and 12 demonstrated that longer period harmonics that were close to the natural periods of these taller buildings were amplified by deep and soft saturated alluvial soils. Strong ground motion stations available at the time of the earthquake in the Manavkuyu region were established on soft grounds where the engineering bedrock with a shear wave velocity of 760 m/s is seated at about 200–350 m. Therefore, it was necessary to conduct deconvolution analyses to come up with engineering bedrock motions that would further be used in convolution runs to come up with realistic ground motions at the sites of the collapsed buildings. Shear wave velocity data captured in seismic surveys, capable of providing reliable data from deeper soil layers, were utilized along with deep borehole logs while establishing the one-dimensional soil response models. A sequential series of deconvolution analyses were then made in order to come up with the engineering bedrock motions. Site response analyses were made on accordingly established 1D model at the site of one of the collapsed buildings yielding acceleration response spectra which were later modified to reflect kinematic soil-structure interaction that would take place underneath the considerably large foundation of the damaged building. It was found that significant soil amplification took place at the building site, and the base shear force obtained based on the kinematic SSI analysis was close to the one found with respect to the 1975 Turkish Seismic Design Code with which the building was designed for.