SEISMICITY
The territory of Macedonia, situated in the Medifterranean seismic belt, is quoted as an area of high seismicity. In the seismic history of Macedonia, the Vardar zone appears as a region where earthquakes occur quite frequently, and the Skopje region is considered to be the most mobile part of the Vardar zone.
The seismicity of Macedonia is related to destructive tectonic processes associated primarily with vertical movement of tectonic blocks. Two regions of specific neotectonic features are well distinguished: West Macedonia, characterized by longitudinal (NE-SE), and Central and East Macedonia with transverse (E W) stretching of principal tectonic morphostructures. The boundaries between this two regions is represented with relatively stable Pelagonian massif (Fig. 1).
Earthquakes of magnitudes 6.0 to 7.8, from ten seismic zones ((Fig. 2, Table 1) have been historically experienced throughout the country. The strongest earthquakes occurred in Pehcevo-Kresna (1904,M=7.8) and Valandovo-Dojran (1931, M=6.7) seismic zones. During the last 100 years few destructive, even catastrophic earthquakes, have been affecting the country.
Moderate scale earthquakes (M<6.0) can cause serious problems, even devastation, in Macedonia and the rural regions in the vicinity of the City of Skopje, since the traditional houses, particularly in the rural regions, are too weak to sustain them without substantial damage. Earthquakes of magnitudes greater than 6.0 on the Richter scale are rather infrequent. However, when they occur, due to the structural weakness of prevailing traditional urban and rural building typology constructed prior to 1964, a widespread devastation might be expected in regions affected,. The earthquakes with magnitudes M=6.9- 7.9 expected from the Pehcevo-Kresna and Valandovo-Dojran seismic zones (Table 1) will be catastrophic not only for Macedonia, but for the entire Balkan region (Bulgaria, Greece and FR Yugoslavia), creating probably the largest natural disaster effects ever occurred in Europe.
Although the seismic history of Macedonia must have been rich with the occurrence of medium-to-strong earthquakes, there is very incomplete documentation on these phenomena until 1905 when the Seismological Institute of Belgrade was founded.
Prior to 1900, the seismic history of Skopje, as part of the Vardar seismic zone, is practically reduced to a rather brief description of the earthquake catastrophes of Scupi in 518 A.D. and that of Skopje in 1555. The old Scupi was situated about 4-5 km northwest of the center of the present Skopje. As ground fissureè extending over 45 km in length and up to 4 meters in width are reported for this earthquake, it seems that it is the strongest shock that has ever occurred in Macedonia. The earthquake of 1555 is said to have demolished a part of Skopje. Both earthquakes are estimated to be of an intensity of XII MCS (catalogues of the Seismological Institute of Belgrade). However, it is believed that the reported values are certainly overestimated.
During this century, the region of Skopje was affected by a series of damaging earthquakes, centered at the village of Mirkovci (42°06’N, 21 °24’E), which lasted from August to September 1921 with a magnitude of 4.6 to 5.1 and intensity of I = VIl-VIlI degrees MCS scale. Besides the local earthquakes, the region of Skopje has suffered several times from relatively distant earthquakes, e.g., from the Urosevac-Gnjilane region in southern Serbia, like in 1921.
In 1963 earthquake (M=6.1, l=lX-X MCS) the City of Skopje was devastated. About 77.4% of total building area (including dwelling houses) was destroyed or heavily damaged and 75.5% of inhabitants were left homeless. The direct economic losses were estimated at 1 billion 1963 US$, or at 15% of the GNP of former Yugoslavia for the year of 1963. Details on damages and effects caused by the 1963 Skopje earthquake of July 26 are presented in Annex A to this report.
The studies on occurred seismicity indicate that only in this century the entire territory of Macedonia have been exposed to intensities larger than VI, 97.8% to intensities equal or larger than VII, 52.2% to intensities equal or larger than VIII, 14.0% % to intensities equal or larger than IX, and 3,9% to intensities equal or larger than X.
Data source (Country report)
1. Name: Zoran Milutinovic
2. Organization: Professor, Institute of Earthquake Engineering & Engineering Seismology, University "St. Cyrie and Methodius", Skopje
3. Course: 1998 Sm
4. Title:SEISMIC HAZARD AND COUNTERMEASURES IN THE CITY OF SKOPJE