Mirror triad of tectonic earthquakes

Abstract

It is natural to call the trinity of foreshocks, main shock and aftershocks a classical triad. The magnitude of the main shock is always greater than the maximum magnitudes of foreshocks and aftershocks. In the classical triad, the number of foreshocks is less than the number of aftershocks. In many cases, foreshocks are completely absent even before very strong earthquakes. In this work, we found a rare but extremely interesting species of triad (we called it the mirror triad), in which the number of foreshocks is greater than the number of aftershocks at the interval of 24 h before and 24 h after the main shock. Quite often, aftershocks are absent in mirror triads at all. In this paper, we described the properties of mirror triads and made an attempt to understand their origin. A schematic classification of tectonic triads is proposed. Keywords: foreshock, main shock, aftershock, Gutenberg-Richter law, Bath law, Omori law, solitary earthquake.