Numerical modeling of preseismic slow movements of crustal blocks caused by quasi-horizontal tectonic forces

A 2D model is proposed for slow crustal movements caused by subhorizontal forces applied to a system of rigid blocks separated by transition zones (faults) filled with viscoelastic material. The aim of the modeling is to explain the main features of tilt anomalies observed prior to earthquakes. It is assumed that an earthquake is prepared within the fault zone, where macroproperties of the fault gouge material are changed due to the increase of microfractures. The fault zones are inclined, and the blocks are allowed to move in both vertical and horizontal directions, as well as to rotate. Numerical experiments were performed for systems of two and seven blocks with different viscosity and rigidity of the fault material. The shape of the anomalies as well as the time delay and decay of the anomaly amplitude with distance from the earthquake preparation zone are explained by the model.