Complexity measure in natural time analysis identifying the accumulation of stresses before major earthquakes

Here we suggest a new procedure through which one can identify when the accumulation of stresses before major earthquakes (EQs) (of magnitude M 8.2 or larger) occurs. By analyzing the seismicity in the frame of natural time, which is a new concept of time introduced in 2001, we study the evolution of the fluctuations of the entropy change of seismicity under time reversal for various scales of different length i (number of events). We find that anomalous intersections between scales of different lengths i are observed upon approaching an extraordinary major EQ occurrence. The investigation is presented for the seismicity in Japan since 1984 including the M9 Tohoku EQ on 11 March 2011, which is the largest EQ ever recorded there, as well as for the seismicity in Mexico where the deadly Chiapas M8.2 EQ in 2017 is Mexico’s largest EQ in more than a century. On the basis of this new complexity measure, a preprint of the present work submitted to the arxiv.org on 5 December 2023 anticipated the recent M7.6 EQ on 1 January 2024 which caused extensive damage in the west coast of Japan.