Breather-type oscillations of the global tectonic shear stress fields

A new way of observing the tectonic waves

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In this paper, two observations of the breather-type oscillating tectonic shear stress field in the Earth's crust are described. The normalized tectonic shear stress from the regional earthquake focal mechanisms is calculated by using the modified moment tensor summation method. The results show that the observed time-development of the normalized tectonic shear stress can be modelled as a breather, which is a spatially localized, time-periodic, oscillatory solution of the sine-Gordon equation. It represents the stress and strain fields, which periodically oscillate in time and decay in space as the distance from the center increases. Two case studies are described. The first was observed during the years 2017–2019 in South America, while the second was observed during the years 1977–1979 south of Japan. The first example is an almost ideal breather. The second example contains some natural noise, but can still be modelled as a breather.

Example of a breather-type oscillation of the shear stress field in South America between 2017 and 2019.