Modelling of Block Structure Dynamics for the Vancea Region: Source Mechanisms of the Synthetic Earthquakes

Abstract

—The main structural elements (blocks) of the Vrancea (Romania)—the East-European plate; the Moesian, the Black Sea, and the Intra-Alpine (Pannonian-Carpathian) subplates—are assumed to be rigid and separated by infinitely thin plane faults. The interaction of the blocks along the fault planes and with the underlying medium is elasto-viscous. The velocity vectors which define the motion of the East-European plate and of the medium underlying the subplates are input model parameters, which are not changed during the numerical simulation. At each time, the displacements of the subplates caused by these motions are defined so that the system is in the quasistatic equilibrium state. When, for some part of a fault plane, the stress exceeds a certain strength level, a stress-drop (a failure) occurs (in accordance with the dry friction model), and it can cause failures in other parts of the fault planes. The failures represent earthquakes and, as a result of the numerical simulation, a synthetic earthquake catalog is produced. Panza et al. (1997) and Soloviev et al. (1999) have determined the ranges for the values of the motion velocity vectors and of the other parameters of the model for which the space distribution of epicenters and the frequency-magnitude relation in the synthetic earthquake catalog are close to those of the observed seismicity. In this paper we study the variation of the slip angle of the synthetic earthquakes as a function of the variation of the model parameters, and we compare our results with observations.