Seismic site investigation and structural amplification based on geotechnical and structural health monitoring

The Ohrid region being one of the most beautiful regions in North Macedonia is also earthquake-prone and a couple of strong earthquakes in the past have caused great disasters. The strongest recorded earthquake was reported in February 1911, with a magnitude of 6.7 at a depth of 15 km [1]. In view of the high seismicity of the Ohrid region, almost all buildings are exposed to risk of a potential earthquake event. The demand for detailed inspections has been initiated in the 80s of the previous century, which has been a pioneering event in the Balkan regions. One of the sites is the Location Tower, which has been reestablished recently and enables real-time monitoring and recording of data. The Location Tower consists of a surface and three downhole instruments up to 125 meters down the bedrock; it is a nine-story building with two instruments installed on the 6th and 9th stories and four instruments installed at the foundation level. Several small to moderate earthquakes have been recorded during the period 2021-2022. Selected results and comparisons of equivalent analysis are presented in this work using real recorded acceleration data from the analyzed site. Based on a number of geophysical and geotechnical investigations, the soil profile of the location is obtained and evaluated both in situ and by laboratory tests. The obtained results present a promising starting point for further complex site response analysis considering both linearity and nonlinearity of the material models, which can be validated by stronger earthquakes in future.