Experimental Evidence for Structural Damage During the 30.10.2020 Samos-Sığacik Earthquake by Laser Vibrometry

Abstract

The Mw 6.9 earthquake of 30.10.2020 that took place to the immediate north of the island of Samos in the Aegean Sea was an important event. It was widely felt in the surrounding areas of both Turkey and Greece. It was an almost pure normal earthquake and recorded by a significant number of strong motion stations deployed in the region. The event caused a small-scale tsunami that led to some damage in the shores of Sığacık, a neighbourhood of the Izmir province to the north of the earthquake source zone. Regional distribution of structural damage was parallel to the ground motion levels. However, the city of Izmir, the third largest city of Turkey and about 60 to 70 km to the north of the epicentral area was severely affected. 117 lives were lost and more than 500 buildings either collapsed or received heavy damage. The majority of collapses and casualties were in the Bayraklı district of İzmir, known for its poor site conditions. This paper reports on a survey that we carried out soon after the earthquake in central Izmir. It relies on laser vibrometry, which was used to measure the dominant frequencies of a series of buildings in low, moderate and heavy damage state. Measurements were carried out remotely in 38 buildings. General structural characteristics of the buildings, such as number of stories, height, structural system and earthquake damage state were visually assessed. The dominant frequencies of vibration were estimated through analysis of vibration data. The fact that the majority of the buildings were more or less similar provided a unique opportunity for comparing their measured natural frequencies of vibration under different levels of damage.