Geophysical research: article

Isostatic recovery flows in the lithosphere
B. Birger
Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia
Journal: Geophysical research
Tome: 18
Number: 4
Year: 2017
Pages: 17-31
UDK: 550.311
DOI: 10.21455/gr2017.4-2
Full text
Keywords: transient creep, isostatic recovery, vertical movements of the Earth’s surface
Аnnotation: Laboratory experiments with rock samples show that their creep at small strains is transient. Therefore we can assume that the lithospheric plates, where strains are small, demonstrate the transient creep that is described by the linear hereditary Andrade rheological model. The effective viscosity that characterizes the transient creep is lower than the effective viscosity at steady-state creep and depends on the characteristic time of the process. The typical duration of isostatic rebound after an initial disturbance of the Earth’s surface is several thousand years, and therefore, the depth distribution of the rheological properties of the lithosphere and crust is different from the distribution that corresponds to slow geological processes. It is shown that when considering the isostatic recovery process, the upper crust can be modeled as a thin elastic plate and the underlying lower crust and lithosphere, as a half-space with transient creep. For such a system, the continuum mechanics equations are solved using the Fourier and Laplace transforms. The solutions are obtained in the form of transverse waves that propagate, with strong attenuation, from the area of the initial disturbance along the Earth's surface and cause its vertical displacements. These solutions, called the inertialess Rayleigh waves, depend on the initial disturbance. In the case of a point initial disturbance, the analytical expression is found for these waves that gives an explicit dependence of the vertical displacements of the Earth's surface on the horizontal coordinates and time. The inertialess Rayleigh waves can be regarded as a mechanism of modern vertical movements of the crust.