Damage distribution in Skopje can be explained in terms of the seismic response of surficial soils. There exists a generally good correlation between the distribution of damage, the thickness of the surficial soil layer, and the predominant periods of microtremors. The most heavily damaged region is covered with about 20 to 30 meters of alluvium, and the predominant period of this alluvium is about 0.36 seconds. The alluvium in this heavily damaged region probably was shaken near its resonant frequency, and soil amplification may have reached three.
The greatest destruction was recorded along a belt which is defined by an abrupt change of the thickness of the alluvium. However, heavy destruction was also recorded on the shallow alluvium side, and no clear explanation exists for this.