A b s t r a c t: Seismic moments (M 0 ) of 79 earthquakes which ed in the Vardar and West Macedonia seismic zones on the territory of the Republic of Macedonia and neighbouring regions within the period 1992-2002 were obtained by inversion of the amplitude spectra of the vertical components of the short-period shear S g and L g surface waves, digitally recorded on the electromagnetic short-period SS-1 and wide-range WR-1 Kinemetrics seismometers at the stations in Skopje (SKO), Ohrid (OHR), Valandovo (VAY), Bitola (BIA) and Kriva Palanka (KPJ). The inversion was done on the Brune dislocation source model and a proper model of the medium. The data used included earthquake local magnitudes (M L ) between 1.5 and 5.2, for the Vardar seismic zone, and between 1.4 and 5.2, for the West Macedonia seismic zone. Moment magnitudes (M W ) of the earthquakes were calculated using the Kanamori formula. Empirical M 0 -M L and M W -M L relations were obtained, the first of the kind for seismic zones in the territory of the Republic of Macedonia. The results also appointed to a differentiation between classes of small and middle-sized earthquakes at M L = 5.2 and to a change in the scaling law of the small earthquakes at M L ≈ 3.0 -3.5 or M 0 ≈ 6·10 13 -1.5·10 14 N·m.
A b s t r a c t: Тhe source mechanism of the earthquake occurred on September 1, 1994, with local magnitude M L = 5.2, in the Bitola region in the south-western part of the Republic of Macedonia, was studied in details. The studies included P-nodal planes determination for the earthquake, synthesizing of P-wave traces with the two P-nodal planes taken separately as fault planes, locating of adjacent earthquakes, as well as a comparison of all the obtained results with the results of the previous macroseismic studies of the earthquake and the neotectonic conditions in the Bitola region. A normal left-lateral fault striking toward WNW was confirmed as a source mechanism of the earthquake. That fault can be associated with the neotectonic Pelister fault, the last being the northern border of the mountain Baba.
A b s t r a c t: The 24 April 2002 M L 5.2 Gnjilane earthquake was studied first through inversion of the S g -L g wave group displacement amplitude spectrum and P-nodal planes determination. The seismic moment, source spectrum corner frequency and Brune equivalent circular fault surface for this shock were obtained, respectively, as M 0 = 6.48·1016 N·m, f 0 = 0.59 Hz and Σ s,eq = 15.2 km 2 . The P-nodal planes for the four strongest aftershocks and the distribution of other aftershocks' epicentres were determined, too, and used in identifying the actual source mechanism of the main shock by a simple method that included also the vertical projections on the Earth's surface of the main shock Σ s,eq with the two main shock P-nodal planes as possible fault planes. It was found that the main shock was caused by a normal right lateral faulting in a plane which struck with an azimuth of 238° and dipped toward NNW under an angle of 22°. This faulting was associated with the shear stressed fault structure along the Pliocene-Quarternary sinking valley of Binačka Morava, and it led to activations of other ruptures as sources of a significant number of aftershocks.
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