Predictive performance of current ground motion models for recorded strong motions in 2020 Samos Earthquake

The 2020 M7.0 Samos earthquake had occurred on the north of Samos Island; however, structural damage was observed in İzmir-Bayraklı, which is located approximately 65 km away from the epicenter. Strong ground motions recorded in İzmir Bay showed unique site amplifications, mostly due to the interaction between the basin and deep alluvial deposit response. The objective of this study is to evaluate the predictive performance of current ground motion models (GMMs) for estimating the recorded strong motions, especially the recordings over or near the Bayraklı-Bornova basin. 66 strong motion stations from Turkey with rupture distance (R_RUP) < 200 km are used in the residual analysis, considering the ambiguities in the magnitude and depth to the top of the rupture estimations. Event terms of the earthquake for tested GMMs are found to be small and lie within the expected scatter, except for T = 0.5–1.5 s spectral accelerations. Event-specific distance attenuation for R_RUP<100 km is consistent with the median predictions of current GMMs; however, the distance scaling for 100 km<R_RUP<200 km are significantly different at high frequencies, indicating faster attenuation for Southwestern Anatolia. Relatively long period (0.5–1.5 s) spectral energy is present in both soft sites on the Bayraklı-Bornova basin and rock/stiff-soil sites on the basin edge and these stations contribute significantly to the positive event terms at T = 0.5–1.5 s. For sites within the basin or close to the basin edge, factors such as the direction of the rupture front, basin width and depth, and the seismic structure of the basin contribute to the ground motion variability.