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We present a dataset of 77 strong ground motion records within 200 km epicentral distance from the 30 October 2020, M7.0 Samos Island (Aegean Sea) earthquake, which affected Greece and Turkey. Accelerograms from National Networks of both countries have been merged into a single dataset, including metadata that have been uniformly derived using a common preliminary source model. Initial findings from the analysis and comparative examination of acceleration time histories, Fourier amplitude spectra and 5%-damped response spectra are discussed along with significant source, propagation path and site effects. The long-period amplifications observed in most records in Izmir bay triggered failures and severe damages in weak structures. Yet, the spectral accelerations are observed to lie below the current and previous design spectra corresponding to the damaged regions. Peak ground motions are used to construct a purely instrumental-based macroseismic intensity map, which is capable of reflecting the actual earthquake damage caused by this considerably large event. Finally, peak ground motions are compared to various ground motion models (GMMs) and deviations are highlighted. Our overall preliminary analysis reveals a strong energy signature of the Samos earthquake in the period range 0.5–1.5 s at many sites, both on rock and soil, whereas records in the heavily hit Izmir city, at an epicentral distance circa 70 km, provide strong indication for additional amplification due to basin effects. At relatively large distance from the earthquake source (> 120 km), several recorded amplitudes are significantly lower than those predicted by many GMMs, implying that further studies are necessary toward the improvement of regional attenuation models. [ABSTRACT FROM AUTHOR]

An investigation of Soil-Structure Interaction (SSI) effects on the seismic response of the Regional Administration building in the island of Lefkas, Greece is performed, based on earthquake recordings from two accelerometric stations installed at the basement of the building and on ground surface at a certain distance from the structure, representing a free-field station. The observed deviation between basement and free-field records is explored by means of a hybrid numerical—analytical formulation in the framework of the substructure approach. To this end, the kinematic part of the interaction mechanism is modeled through commonly employed analytical transfer functions between ground surface and foundation base, while a detailed 3D mass-distributed Finite Element model is analyzed under both fixed and flexible supports to explore the seismic response of the building, as affected by inertial SSI effects. The comparison between predicted and recorded response shows a kinematic dominated response of the foundation that is characterized by strong filtering of the free-field motion at ground surface. Accordingly, various repercussions due to the potential underestimation of the seismic hazard from recording stations housed at the basement of buildings are discussed. Numerical results demonstrate also that soil compliance may have an important effect on the seismic demand quantified in terms of interstorey drifts of the building. Finally, a simplified MDOF lumped-mass stick model of the superstructure is also analyzed under flexible-base conditions, leading to a substantial overprediction of interstorey drifts compared to the 3D model. [ABSTRACT FROM AUTHOR]

Acheiropoietos in its current state is a typical Early Byzantine three-aisled timber-roofed basilica with narthex and galleries. During the destructive earthquake of June 20, 1978, the basilica suffered significant damage. In the following years, ambient vibration measurements were performed at the damaged structure before any intervention and main eigenperiods of vibration were calculated. In 1990s, an extensive structural restoration project was undertaken aiming at the provision of diaphragms of controlled shear strength and rigidity at the level of the timber floors and roofs of the galleries. Horizontal steel frames were placed at the perimeter of these diaphragms providing the required diaphragmatic response. The interventions were intended to support the long north and south walls and galleries of the basilica by its stiffer east and west walls against horizontal actions. Within the framework of the present study, the efficiency of the interventions to achieve the desired diaphragmatic response was investigated by measuring the structure’s response to ambient vibration. The in situ measurements and the postprocessing data document that the timber diaphragms are actually behaving as rigid levels. Therefore, it is concluded that the implemented interventions on the basilika assure its proper diaphragmatic function, improving thus successfully its dynamic behavior in future earthquake excitations, according to the redesigned structural approach. [ABSTRACT FROM AUTHOR]

In the framework of the SESAME project one of the tasks was the compilation of all available ambient noise measurements within urban environments affected by historical or/and recent strong earthquakes in Europe. The aim of such a task was to give an answer to the question; “ How does horizontal-to-vertical ambient noise spectral ratio compare with damage in modern cities?”. For this purpose five European urban areas, namely, Angra do Heroismo (Portugal), Fabriano and Palermo (Italy), Thessaloniki and Kalamata (Greece) were selected for which spatial damage information was available either in terms of modified Mercalli intensity or in EMS98 damage grades. The geological setting of the examined sites as well as the causative earthquakes are satisfactorily known. Ambient noise recordings compiled for all examined sites have been homogeneously processed by a technique developed and agreed upon SESAME project. Using a standard multivariate statistical analysis, namely, factor analysis and canonical correlation, the horizontal-to-vertical ambient noise spectral ratio (HVNSR) is correlated with damage pattern observed within examined urban areas. Results show that, in some cases (Thessaloniki, Palermo), the HVNSR seems to be able to differentiate between areas previously shown to be associated with higher damage. In other cases however (Angra do Heroismo, Fabriano, Kalamata), the correlation is not statistically significant indicating thus the complex character of the parameters involved, implying that currently there is no a straightforward way that a value of HVNSR can correctly predict the extent to which a given region will be associated with increased damage. [ABSTRACT FROM AUTHOR]