Accumulation of Stress and Strain due to an Infinite Strike-Slip Fault in an Elastic Layer Overlying a Viscoelastic Half
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Pure and Applied Geophysics
Accumulation of Stress and Strain due to an Infinite Strike-Slip Fault in an Elastic Layer Overlying a Viscoelastic Half Space of Standard Linear Solid (SLS) DEBABRATA MONDAL,1 PIU KUNDU,1 and SEEMA SARKAR (MONDAL)1 Abstract—Viscoelastic behaviour of materials at the lithosphere-asthenosphere boundary is observed in this paper. The observed post-seismic and aseismic deformation help us to understand the rheological properties of the mantle and asthenosphere. A quasi-static model having homogeneous, isotropic, elastic material overlying viscoelastic material of a standard linear solid (SLS) is considered. A long strike-slip fault of finite width inclined to the free surface due to a sudden movement has been studied in this work. Analytical solutions for displacement, stresses and strains are obtained before and after fault movement using a technique involving the use of Green’s functions and integral transforms, assuming that tectonic forces maintain a shear strain far away from the fault. The effect of aseismic fault movement across it is found to depend on distance, dimension, relative position and other characteristics of the fault. Also, the effect of different inclinations, elastic layer thickness and slip magnitude have been studied. The study of such earthquake fault dynamical model helps us to understand the mechanism of the lithosphere-asthenosphere boundary. Keywords: Strike-slip fault, Standard linear solid, Green’s function technique.
1. Introduction Earthquake-generating faults differ in geometrical size and shape and are generated due to various types of movement across active seismic fault zones, such as the San Andreas fault zone of California, the North Anatolian fault zone of Turkey and the Atalanti fault zone of central Greece. When geologists and seismologists are modelling the dynamics of earthquakes (which is one of the main concerns of theoretical seismology at present) in the seismically active regions of the earth, they have to take into account
1 Department of Mathematics, National Institute of Technology Durgapur, Durgapur, India. E-mail: [email protected]; [email protected]
the period of seismic activity (when an earthquakes takes place) as well as the apparently aseismic period during which slow and continuous aseismic surface movements are observed in seismically active regions. These aseismic surface movements indicate slow aseismic changes of stress and strain in that region. If the stress becomes sufficiently large to overcome the frictional and cohesive forces, this may lead to sudden/creeping fault movement. The deformation and stress responses of an elastic or viscoelastic half space due to the dislocation sources have been investigated by many researchers. The work involving static ground deformation in an elastic medium was initiated by Chinnery (1961) and Maruyama (1964, 1966). Various theoretical models in this direction were later formulated by a number of authors, including Rybicki (1971, 1973), Sato (1972) and Sen et al. (1993)
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