Dynamic estimate of seismic danger based on multifractal properties of low-frequency seismic noise

A new method of dynamic estimate of seismic danger is presented which is based on estimating multifractal properties of low-frequency seismic noise. The efficiency of the method is illustrated by the analysis of seismic noise from broadband seismic network F-net in Japan. The analysis of multifractal properties of low-frequency seismic noise from Japan seismic network F-net since the beginning of 1997 allowed a hypothesis about approaching Japan Islands to a future seismic catastrophe to be formulated at the middle of 2008. The base for such a hypothesis was statistically significant decreasing of multi-fractal singularity spectrum support width mean value. The peculiarities of correlation coefficient estimate within 1 year time window between median values of singularity spectra support width and generalized Hurst exponent allowed to make a decision that starting from July 2010, Japan come to the state of waiting strong earthquake. This prediction of Tohoku mega-earthquake, initially with estimate of lower magnitude as 8.3 only (at the middle of 2008) and further on with estimate of the time beginning of waiting earthquake (from the middle of 2010), was published in advance in a number of scientific articles and abstracts on international conferences. The analysis of seismic noise data after Tohoku mega-earthquake indicates increasing probability of the 2nd strong earthquake within the region where the north part of Philippine Sea plate is approaching island Honshu (Nankai Trough). This region is characterized by relatively low values of singularity spectrum support width which is an indicator of seismic danger. In one paper (Sobolev in Izv Phys Solid Earth 47:1034–1044, 2011 ), the low-frequency seismic noise at the same range of periods was investigated retrospectively using data from the stations of broadband network IRIS which are located around the epicenter of Tohoku mega-earthquake with a distance up to 1,200 km. It was shown that the variance of the noise and the number of high-amplitude asymmetric impulses were grown dramatically before the event for stations which are located within the radius up to 500 km from the epicenter.