Solitary waves in crustal faults and their application to earthquakes

Abstract

The problem related to crustal fault dynamics consists of identification of the processes and parameters that are responsible for sliding regimes in the faults. The concepts according to which the transition from creep to stickslip along the crustal fault, in most cases accompanied by a tectonic earthquake, is caused by geometrical inhomogeneities of fault surfaces, a decrease of friction in some segments of the fault and by anomalies of the pore pressure, are considered to be conventional (Ben-Zion and Rice 1995). The deformational waves propagating along the faults and excited by elastic-rebound in the foci of the past earthquakes may also initiate seismic slips in crustal faults (Ulomov 1993). The deformational waves detected from changes in the geophysical fields (Nikolaevskiy 1998) are accompanied by migration of seismic activity in a number of cases (Ulomov 1993). The existence of these waves is known to be confirmed in the course of experimental studies of slow deformation processes in the crust (Nevskiy 1994). A lot of direct and indirect evidences (Nikolaevskiy 1996) show that slow tectonic deformations are propagating as solitary waves - solitons. For this reason, theoretical studies (Garagash 1996, Nikolaevskiy 1996, Nikolaevskiy and Ramazanov 1986) aimed at developing mathematical models that lead to soliton-like solutions and, at the same time, reflect the main features of wave deformation process occurring in the crust are of topical interest. In this chapter it is shown that local deformation effects at the mesoscopic level related to decrease of friction at the contacts of inhomogeneous fault surfaces may cause solitary waves of activation whose evolution leads to macroscopic processes as seismic slips in crustal faults. The model suggested describes the dynamics of relative displacements of fault surfaces including retarding and accumulation of energy necessary to provide a stick-slip process. As it is well known, the stick-slip is a necessary element to provide seismic events inside the earthquake focus. Analysis is made of asperity and friction effects in the fault on the evolution of velocity of waves of activation and also the amplitude and frequency of periodical load on fault dynamics. A relative role of different processes in the initiation of seismic slip is investigated. © Springer-Verlag Berlin Heidelberg 2006.