Multifractal and Entropic Properties of Seismic Noise in the Japanese Islands

The article examines the behavior of seismic noise fields over the Japanese islands recorded by the F-net seismic network for 1997-2025. The paper uses nonlinear noise statistics: the entropy of the wavelet coefficient distribution, the Donoho-Johnston (DJ) wavelet index, and the multifractal singularity spectrum support width. These parameters were chosen because their changes reflect the complication or simplification of the noise structure. Changes in the structure of seismic noise properties are analyzed in comparison with a sequence of strong earthquakes. Using a model of the intensity of interacting point processes, the effect of the leading of local noise property extrema relative to the seismic event times is estimated. Using the Hilbert-Huang decomposition, the synchronization of the amplitudes of the envelopes of noise property time series for different IMF levels is estimated. A sequence of weighted probability density maps of extreme values of noise properties is analyzed in comparison with the mega-earthquake of March 11, 2011 and the preparation of a possible next strong seismic event.