The deformation behaviour of a stable continent and its seismicity

What is it about?

The present analyses indicate that the maximum principal stress axis of the Indian plate interior does not coincide with the plate motion vector. The strain rate curves for the Indian plate indicate interference of two different orders of deformation. The magnitudes of the first-order maximum strain rates are lower than local extreme strain rates of the second-order deformation. It has been shown herein that the oblique motion of the Indian plate with respect to a state of dominant strike-slip deformation in the Indian plate interior is partitioned into a principal deformation zone, synthetic shear and antithetic shear. The strain rates along these regional shear zones show complex association of second-order high shortening rate coinciding with high extension rate. The earthquakes of the Indian plate interior are interpreted to be results of periodic accumulation of stress ⁄ strain due to shortening and release of strain along the same directions during the extension.

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Why is it important?

Strain is a tensor. Deformation of a circle produces an ellipse (strain ellipse). Averaging of strain value followed in many publications removed important vectorial property of strain. For example averaging of all lines passing through the center of an ellipse will give the diameter of circle (i.e. indicate no deformation). The paper demonstrates how to determine crustal strain from GPS site vector data. Results indicate very high strain value in particular directions of a stable continent.