ИСТИНА

The results of the analysis of the properties of low-frequency seismic noise on the Japanese islands from the beginning of 1997 to September 2018 are presented. The considered time interval includes one of the largest recent seismic catastrophes - the Tohoku earthquake on March 11, 2011. The presence of a network of seismic observations provides a unique opportunity to investigate the preparation of a strong earthquake affects the change in the properties of seismic noise both in time and in space. Analysis of the clustering of daily multi-fractal and entropy properties of seismic noise in a 1-year sliding time window, averaged over all stations of the network, allowed us to find a 2.5-year periodicity established since early 2003, which correlates with the occurrence of strong earthquakes in Japan. The study of the features of the spatial distribution of seismic noise properties makes it possible to put forward a hypothesis about the increased risk of the next mega-earthquake in Japan in the contact area of the northern tip of the Philippine Oceanic Plate with Honshu, in the area of the Nankai Trough, near Tokyo. In addition to the network of seismic observations on the Japanese islands, there is a dense network of fixed GPS points, for which since the beginning of March 2015 there are observations with a time step of 5 minutes. The availability of such measurements makes it possible to supplement the analysis of the properties of seismic noise and to calculate the degree of correlation of GPS data at any point from measurements at neighboring stations. As a result, it turned out that the most intense spot of increased correlation of the earth tremor, measured by GPS, is located in the Nankai Trough with its center at 34°N and 138°E.