Abstract
A b s t r a c t: The 24 April 2002 ML 5.2 Gnjilane earthquake was studied first through inversion of the Sg – Lg 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 M0 = 6.48·1016 N·m, f0 = 0.59 Hz and Σs,eq = 15.2 km2. 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 Σs,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.
Highlights
On 24 April 2002, at 10:51 GMT, a moderate earthquake occurred near the town of Gnjilane in the region of Kosovo
The present study aims to find the actual source mechanism and size of the 24 April 2002 ML 5.2 Gnjilane earthquake, as well as to sketch some characteristics of the whole corresponding seismic cycle
According to all seismic and non-seismic data, the long-term tectonic stressing in the first phase of the seismic cycle is most often a shear stressing, and, the most probable source model for the earthquakes is a dynamic faulting – a rupturing with relative slip of rupture’s walls that propagates in a short time and with a velocity that increases rapidly, having the S wave velocity as upper limit
Summary
On 24 April 2002, at 10:51 GMT, a moderate earthquake occurred near the town of Gnjilane in the region of Kosovo. The neotectonic activity in Kosovo is characterized by permanent uplifting of the terrain It had passed a phase of flattening of the terrain through erosion and denudations (pre-orogenesis), which was proceeded by orogenesis, i.e. by differential, predominantly vertical movements of the first and second order tectonic structures under regional tectonic stresses that mainly resulted in an approximatively E-W oriented shear stressing. The source of the strongest earthquake observed in the last century (10 August 1921, 14 h 10 min GMT, ML = 6.1) was associated with the fault structure along the approximatively E-W oriented valley of the river of Binačka Morava
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