Abstract
The paper considers synchronous continuous records of microseismic background obtained within a month before the Kronotskii (Kamchatka) December 5, 1997, earthquake (M = 7.8) at six IRIS broadband stations that are located in a large region extending from central European Russia (the town of Obninsk) to the Far East (Kamchatka and Sakhalin). By averaging and downsampling, initial records were discretized at an interval of 30 s and the microseismic background was examined in the range of periods from 1 min to 2.4 h, after scale-dependent trends due to the effects of tides and temperature variations had been removed. Microseismic fluctuations were analyzed with the help of estimates of the evolution of their multifractal singularity spectra in a moving time window 12 h wide. As the criterion characterizing the background properties in a current time window, we took the values of the generalized Hurst exponent α* realizing the maximum of the singularity spectrum. Hidden synchronization effects of a microseismic field preceding a seismic event are identified by estimating the evolution of the spectral measure of coherent behavior of α* variations in a moving time window 5 days long for various combinations of jointly analyzed stations.
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