Fractal ULF signatures related to seismic processes

Abstract

Abstract. In order to detect seismo-related patterns that manifest themselves in fractal properties of ULF magnetic field variations, the fractal and multifractal analyses of the ULF data obtained from several stations were performed. As a result, two different behaviors of fractal parameters of the ULF magnetic field variations were detected. The first one has the certain co-seismic character and manifests itself in significant increase in fractal dimension synchronous with the rise of seismic activity. Another pattern can be interpreted as a manifestation of the seismic preparation processes, which is characterized by the significant gradual decrease in fractal dimension during the extended time period of several months.Also a new procedure of the local geomagnetic activity (LGA) level estimation was proposed. A correlation between the geomagnetic activity and the fractal dimension, and, consequently, the necessity of taking into a consideration the LGA level was demonstrated.Key words: fractal analysis, ULF variations, seismo-electromagnetic patterns. IntroductionThe modern geophysics has several challenging problems. One of those important problems is a possibility to find out some reliable precursor signatures of strong seismic events, and the promising candidate as a role of such a process can be the seismo-electromagnetic coupling. During the last decades several different models describing such a kind of coupling were proposed by different researchers (Molchanov and Hayakawa, 1998, 2008;Molchanov, 1999;Surkov and Pilipenko, 1999;Surkov, 1999;Hayakawa and Molchanov, 2002;.The most promising frequency range of seismogenic emissions is supposed to be ULF because ULF emissions originated from different processes in the focal zone can reach the Earth's surface from the focal depths of several tens kilometers. Different parameters of the ULF signals could be analyzed: polarization ratio, power spectrum, fractal dimension (Hayakawa et al., 1996(Hayakawa et al., , 1999Hattori et al., 2002Gotoh et al., 2003;Smirnova et al., 2004;Ida et al., 2005;Ida and Hayakawa, 2006;Molchanov and Hayakawa, 2008). Hayakawa et al. (1999) carried out the first attempt of fractal analysis for the 1993 Guam earthquake by means of the frequency spectrum slope estimation. Later Smirnova et al. (2004), Gotoh et al. (2004) and Ida et al. (2006) have developed different kinds of fractal estimations and also have extended them from the mono to multifractal analyses (Ida and Hayakawa, 2005). Nevertheless, the number of events analyzed is extremely small, so that we need to increase the amount of analyzed events in order to obtain certain patterns or concrete precursor signatures of earthquakes. In this sense we have performed the fractal analysis of ULF data from several Japanese ULF stations in order to detect any seismo-related patterns and to classify them.In our analysis we have used the most complete ULF data (with minimal amount of gaps) from nine Japanese ULF stations (Kakioka, Mochikoshi, Unobe, Fudago, Iyogatake, Kagoshima, Seikos...

Fractal analysis of ULF electromagnetic emissions in possible association with earthquakes in China

“…Because Mezentsev et al (2009) have analyzed the fractal dimension of ULF geomagnetic data at different stations and over long-term data, they have found that the geomagnetic storm tends to have a significant effect and that the fractal dimension always decreases for geomagnetic storms.…”