3rd Croatian Conference on Earthquake Engineering 3CroCEE

Near-surface characterization, i.e., determination of the physical-mechanical characteristics of the soil and rock masses that constitute the terrain structure is crucial in avoiding catastrophic consequences during seismic and geotechnical hazards. Geophysical techniques can provide a comprehensive understanding of subsurface conditions, including the presence of weak zones, local anomalies, groundwater levels, slope stability, and tectonic structures, offering valuable information for assessing potential risks and hazards. Surface seismic methods are non-invasive and widely accepted geophysical techniques for near-surface characterization, and have been used in IZIIS for an extended period. This paper presents two case studies of geophysical surveys conducted for site characterization purposes. Combined seismic method surveys were performed in Strumica, N. Macedonia, at the site of the Orta Mosque. The primary motivation for this study was the appearance of cracks in the Orta Mosque building, which have progressively expanded over time. A similar procedure was applied at the location for tunnel construction in Aleksinac, Serbia. The main objective in both cases has been definition of the seismo-geological characteristics, potential anomalies, local tectonic deformations, and discontinuities in the terrain structure. The seismic models derived from the seismic refraction survey at the Orta Mosque site indicate layers of unconsolidated deposits, with a maximum recorded depth of over 20 meters. The seismic reflection sections, displayed in 3D to provide a more realistic view of the discontinuities and the slope of the bedrock, indicate deformations and local disturbances in the deeper layers. The variation in the thickness of the surface layers, as recorded in the seismic refraction profiles conducted at the tunnel site in Serbia, indicates anomalies, i.e., unstable zones, which are also identified in the deeper layers through reflection profiles. Interpreted discontinuities and deformations in the terrain structure in both case studies point to underlying dynamic processes.