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Within the presented research, model tests were performed in 1-g conditions to investigate the liquefaction potential of Skopje sand as a representative soil from the Vardar River’s terraces in N. Macedonia. A series of shaking table tests were performed on a fully saturated, homogeneous model of Skopje sand in the newly designed and constructed laminar container in the Institute of Earthquake Engineering and Engineering Seismology (IZIIS), Skopje, N. Macedonia. The liquefaction depth in each shaking test was estimated based on the measured acceleration and pore water pressure as well as the frame movements of the laminar container. The surface settlement measurements indicated that the relative density increased by ~12% after each test. The observations from the tests confirmed that liquefaction was initiated along the depth at approximately the same time. The number of cycles required for liquefaction increased as the relative density increased. As the pore water pressure rose and reached the value of the effective stresses, the acceleration decreased, thus the period of the soil started to elongate. The results showed that the investigated Skopje sand was highly sensitive to void parameters and, under specific stress conditions, the liquefaction that occurred could be associated with large deformations. The presented experimental setup and soil material represent a well-proven example of a facility for continuous and sustainable research in earthquake geotechnical engineering.

<p>Surface seismic methods are among the most popular, widely accepted, geophysical methods for near-surface characterization. The most practical and effective way to perform in-situ measurements and data processing using different seismic methods as are seismic refraction, seismic reflection and MASW method in an integrated approach is presented in this paper. Each method has some advantages and limitations, but their application in an integrated approach provides higher accuracy in subsurface modeling. The same seismic equipment and, in most of the cases, the same acquisition parameters were used, enabling time and cost effective survey for subsurface characterization. The choice of these parameters was not random. Experimental research by use of the above-mentioned seismic methods was carried out in a long period in order to define the optimal parameters for successful application of an integrated technique in future research. During this survey, particular attention was paid to the influence of the acquisition parameters on the dispersion image resolution in the MASW surveys and extraction of an effective dispersion curve.</p><p>The results of the performed surveys at characteristic locations in R. North Macedonia are presented to show the efficiency of the combined methods approach.</p>

The large number of catastrophic earthquakes that have occurred worldwide and their consequences point out the fact that the seismo-geological structure of the terrain represents an amplitude-frequency modifier of the seismic effect. The unconsolidated sediments lying upon the bedrock as well as the variations of the bedrock topography may increase the amplification potential of the seismic effects depending on their physical properties and thickness. From this aspect, there arises the need for obtaining as realistic as possible insight into the structure of the terrain, i.e., definition of the geometry of the sedimentary basins. Particular attention in this study was paid to definition of thickness variation of alluvial unconsolidated deposits that constitute the Skopje sedimentary basin, reaching a depth of down to 200 m, as well as the topography of the Neogene sediments present in the terrain base. For that purpose, preliminary 3D geological modelling was done by interpolation of a number of boreholes made in the urban area of Skopje city. Geophysical surveys were performed by application of active and passive seismic methods as are seismic refraction, seismic reflection, Multichannel Analysis of Surface Waves (MASW), Refraction Microtremor (REMI) and Horizontal-to-Vertical Spectral Ratio (HVSR) for the purpose of defining the variation of the shear-wave velocity Vs through different lithological layers as well as upgrading and improving the accuracy of the 3D model. Of particular importance for this survey was the implementation of fast, economical and efficient procedure by using the combined seismic methods approach, which enabled seismo-geological modeling to different scales as well as comparative analysis of the results and verification of their accuracy.