Slow deformations of the Earth's crust and their relation to earthquakes in the U.S.S.R.

Abstract

Slow tectonic deformations of the Earth's crust and the associated stresses give rise to faulting and earthquakes. A correlation between earthquakes and slow recent deformations may be observed by geophysical and geodetic methods for short periods of time (up to tens of years). A correlation between earthquakes and long-continued deformations is determined by a tectonophysical interpretation of geomorphic and tectonic data. Thorough investigations of slow deformations by a number of various methods are necessary to learn the processes preceding earthquakes. For the different methods of investigation, corresponding sizes of the objects of study and periods of time differ by many orders of magnitude. First, one consequence of such a change of scale is that we obtain different mean velocities of movement and crustal strain rates. Second, each particular method brings out qualitatively different peculiarities of crustal deformations. With small objects and short periods of time, we get violent irregularities in deformation processes and faulting in space and time. The mosaic small-block structure of the crust becomes especially prominent and non-tectonic deformations may exceed tectonic ones in amplitude. With large objects and long periods of time, the effect of summing up deformations and fault displacements over time and area becomes foremost in importance; a general tendency of large-scale tectonic processes becomes apparent.