Abstract
Abstract. A fault system made of two segments or asperities subject to a constant strain rate is considered. The fault is modelled as a discrete dynamical system made of two blocks coupled by a Maxwell spring dashpot element and pulled at constant velocity on a rough plane. The long-term behaviour of the fault is studied by calculating the orbits of the system in the phase space. The model shows the role of viscoelastic relaxation in the Earth's crust in controlling the occurrence times of earthquakes. If a viscoelastic coupling is present, earthquakes are anticipated or delayed with respect to the elastic case. The limit cycles made of two alternate asperity failures, which are observed in the case of purely elastic coupling, are no longer produced. The model is applied to the 1964 Alaska earthquake, which was the effect of the failure of two asperities and for which a remarkable post-seismic relaxation has been observed in the subsequent decades. In such a fault system, viscoelastic coupling of the asperities appears to have a great influence on the occurrence times of earthquakes.
Highlights
The seismic activity of a fault is controlled by the applied tectonic stress, due to plate motion, and by the stresses transferred by dislocations on neighbouring faults
The model presented in this paper investigates the interaction between two asperities in the presence of a viscoelastic coupling
We presented a complete analytical solution for the four modes of the system. On this basis we calculated the orbits of the system in the phase space in order to establish how the different physical quantities control the occurrence times and the source functions of the earthquakes generated by the system
Summary
The seismic activity of a fault is controlled by the applied tectonic stress, due to plate motion, and by the stresses transferred by dislocations on neighbouring faults. Fault interaction plays a key role in determining the occurrence times of earthquakes. A role in this process is played by the rheological properties of the Earth’s crust. The static stress fields produced by seismic dislocations undergo a certain amount of relaxation during the interseismic intervals, which may have durations of hundreds of years (Chen and Molnar, 1983; Dragoni et al, 1986; Kusznir, 1991; Kenner and Segall, 2000). In a fault system, such a long-term variation of stress alters the stress distribution on faults and modifies the occurrence times of seismic events In a fault system, such a long-term variation of stress alters the stress distribution on faults and modifies the occurrence times of seismic events (e.g. Chery et al, 2001; Lynch et al, 2003; Smith and Sandwell, 2006; Piombo et al, 2007)
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