A 2-D model for tilt and strain fields associated to earthquakes in crustal block structures

A 2-D model for slow crustal movements, including tilt and strain anomalies before earthquakes as well as shape and time lag of each preseismic anomaly with respect to the time of origin of the corresponding earthquake, is proposed. The model represents a numerical study to evaluate the behavior of a series of crustal rigid blocks separated by narrow fault zones filled with viscoelastic material. Rheology of the fault material is described by constitutive equations of standard linear solid. Vertical displacement and rotation of the blocks result from the vertical uplift of one (central) block due to a vertical Force. Displacements and tilts of blocks are computed from a system of linear differential equations which are solved numerically. The main characteristic feature of the model is that the viscoelastic parameters of the fault zone, where fracture occurs (at the boundary of the rising block), may change in time? simulating the earthquake preparation. Numerical modelling shows that tilt behavior at successive blocks reveals anomalies which are similar in shape to the observed ones. The anomalies are of opposite signs in adjacent blocks, and show a time lag with distance from the fracturing zone. (C) 1998 Elsevier Science B.V