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

Abstract

Abstract. The long-term data (during the period of 1 March 2003 through 31 December 2006) of ULF geomagnetic variations observed at Kashi station (geographic coordinates: 39.5 • N, 76.0 • E) in China have been used to investigate the long-term variation of fractal dimension of ULF emissions. We have studied the changes in fractal dimension in association with several earthquakes around the observation station. It is then found that a significant change (or decrease) in the fractal dimension of the Z component took place before the 1 September 2003 earthquake, which lends a further support to our previous finding based on our improved polarization analysis for the same earthquake. The results obtained are discussed in the contexts of a few aspects (detectability of seismogenic emissions, comparison with previous results by other analysis methods, the importance of fractal analysis in the nonlinear process of the lithosphere and earthquake prediction).

Comment on "Fractal analysis of ULF electromagnetic emissions in possible association with earthquakes in China" by Ida et al. (2012)

“…Up to now no strong evidence has been provided to reject the findings of these reviews. Ida et al (2012) criticized the findings of some of these papers, such as, Campbell (2009) and Thomas et al (2009a, b), but they did not provide any solid evidence in support of their weak criticism. Among these reviews, there are the studies by Masci (2010Masci ( , 2013, which demonstrated that the fractal analysis of the geomagnetic field in the ULF band is not a good indicator of an imminent earthquake.…”

“…These papers reported a relation between the fractal dimension variations and the occurrence of strong earthquakes such as the 1993 Guam earthquake, the 1996 Biak earthquake, and the 2000 Izu earthquake swarm. Ida et al (2012) failed to address the review by Masci (2010) that demonstrated that the fractal precursors documented in these papers are signals that are part of normal geomagnetic activity, which therefore cannot be described as earthquakerelated anomalies.…”

“…Among these reviews, there are the studies by Masci (2010Masci ( , 2013, which demonstrated that the fractal analysis of the geomagnetic field in the ULF band is not a good indicator of an imminent earthquake. On the contrary, Ida et al (2012) referred to several papers that identified increases in the fractal dimension of the ULF geomagnetic field H component as earthquake precursors. These papers reported a relation between the fractal dimension variations and the occurrence of strong earthquakes such as the 1993 Guam earthquake, the 1996 Biak earthquake, and the 2000 Izu earthquake swarm.…”

“…The first comment concerns the set of data analyzed by Ida et al (2012). In a previous paper (Ida et al, 2008), the authors conducted a polarization ratio analysis performed by using the same magnetic dataset of Ida et al (2012).…”

“…In their study, Ida et al (2012) analyzed magnetic data (1 Hz sampling rate) recorded by a triaxial fluxgate magnetometer system in Kashi, China, during March 2003-December 2006. The first comment concerns the set of data analyzed by Ida et al (2012).…”