Geophysical processes and biosphere: article

Аnnotation: The results of the analysis of the properties of low-frequency seismic noise on the Japanese islands from early 1997 to March 2018 are presented. This time interval includes one of the largest seismic disasters of the last time - the Tohoku earthquake of March 11, 2011. The presence of a dense network of seismic observations provides a unique opportunity to investigate how the preparation of a strong earthquake is reflected in the changing properties of seismic noise both in time and space. Analysis of the clustering of the daily multi-fractal and entropic properties of seismic noise in a 1-year moving time window averaged over all stations of the network made it possible to find a 2.5-year periodicity, established since the beginning of 2004, which correlates with the occurrence of strong earthquakes in Japan. The study of the features of the spatial distribution of seismic noise properties allows us to propose a hypothesis about the increased danger of the next mega-earthquake in Japan in the area of contact of the northern boundary of the Philippine oceanic plate with island Honshu, in the Nankai deep-water trough area, not far from Tokyo. In addition to the network of seismic observations on the Japanese islands, there is a dense network of fixed GPS points, for which, from the beginning of March 2015, there are observations with a time step of 5 minutes. The presence of such measurements makes it possible to supplement the analysis of seismic noise properties 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 Earth’s surface tremor, measured by means of GPS, is located in the Nankai trough with the center at the point 34ο N and 138ο E.