On the seismogenic increase of the ratio of the ULF geomagnetic field components

Abstract

Following the paper by Fraser-Smith et al. (1990), many scientists have focused their research on the ULF geomagnetic field pulsations in the hope of finding possible anomalous signals caused by the seismic activity. Thereafter, many papers have reported ULF geomagnetic field polarization ratio increases which have been claimed to be related to the occurrence of moderate and strong earthquakes. Even if there is no firm evidence of correlation between the polarization ratio increase and seismic events, these publications maintain that these "anomalous" increases are without doubt precursors of pending earthquakes. Furthermore, several researchers suggest that these seismogenic signals may be considered a promising approach towards the possibility of developing short-term earthquake prediction capabilities based on electromagnetic precursory signatures. On the contrary, a part of the scientific community emphasizes the lack of validation of claimed seismogenic anomalies and doubt their association with the seismic activity. Since earthquake prediction is a very important topic of social importance, the authenticity of earthquake precursors needs to be carefully checked. The aim of this paper is to investigate the reliability of the ULF magnetic polarization ratio changes as an earthquakes' precursor. Several polarization ratio increases of the geomagnetic field, which previous researchers have claimed to have a seismogenic origin, are put into question by a qualitative investigation. The analysis takes into 2 account both the temporal evolution of the geomagnetic field polarization ratio reported in previous papers, and the global geomagnetic activity behaviour. Running averages of the geomagnetic index K p are plotted onto the original figures from previous publications. Moreover, further quantitative analyses are also reported. Here, nine cases are investigated which include seventeen earthquakes. In seven cases it is shown that the suggested association between the geomagnetic field polarization ratio increases and the earthquake preparation process seems to be rather doubtful. More precisely, the claimed seismogenic polarization ratio increases are actually closely related to decreases in the geomagnetic activity level. Furthermore, the last two investigated cases seem to be doubtful as well, although a close correspondence between polarization ratio and geomagnetic activity cannot be unambiguously demonstrated.

On the multi-fractal characteristics of the ULF geomagnetic field before the 1993 Guam earthquake

“…The presumed precursors of the Guam earthquake can be essentially reassumed in the increase of the fractal dimension of the geomagnetic field components and in the change of the ratio between the integrated power, in a fixed frequency band, of the vertical component and the horizontal components of the geomagnetic field, the so-called polarization ratio. However, recently Masci (2010Masci ( , 2011a and Thomas et al (2009b) have demonstrated that these presumed precursors of the Guam earthquake were normal disturbances closely related to changes of the global geomagnetic level and then not induced by the seismic activity. Ida et al (2005), hereafter cited as IDA, performed multifractal detrended fluctuation analysis (MFDFA) of ULF geomagnetic field data from the Guam observatory which is located 65 km away from the epicentre of the 1993 Guam earthquake.…”

“…They excluded any correlation between the changes of the geomagnetic field multi-fractal parameters and the geomagnetic activity since the presumed multi-fractal precursors occurred during a geomagnetic quiet period. This is an oversimplified assumption since we must not consider the level of the geomagnetic activity but its variations which induce changes in several magnetic parameters as well as in the fractal characteristics of the geomagnetic field (see also Masci 2010Masci , 2011a. Figure 1 shows the time series of the MFDFA parameters reported by IDA as daily and 9-day running average values.…”

“…However, since previous studies do not show strong evidence of correlation between the presumed magnetic precursors and seismic events, many scientists do not agree that these signals are really related to the earthquake occurrence. As a consequence, these researchers seriously put into question previous observations of magnetic ULF earthquake precursors and have published their findings (see Campbell, 2009;Masci, 2010Masci, , 2011aMasci, , b, 2012aThomas et al, 2009a, b) giving rise to an intense re-examination process of controversial scientific claims (see also Fraser-Smith et al, 2011;Masci, 2012d;Thomas et al, 2012).…”

Comment on "Ultra Low Frequency (ULF) European multi station magnetic field analysis before and during the 2009 earthquake at L'Aquila regarding regional geotechnical information" by Prattes et al. (2011)

“…Likewise, we should also not expect that in an observation site, (e.g. L'Aquila), a close correspondence between K p and the standardized polarization exists during a long time range (see Masci, 2011a). In brief, as claimed by Masci (2011b), the main issue is: a close correspondence between changes of an ULF geomagnetic field parameter (in this case the standardized polarization) and K p indicates that these changes are part of normal global geomagnetic field variations driven by solar-terrestrial interaction.…”

“…Obviously, it is likely that an anomalous variation of a geomagnetic field parameter may be observed before the occurrence of an earthquake, but relating the anomaly with the seismic event without further validations is just an oversimplified conclusion. As a consequence, some authors (see Campbell, 2009;Thomas et al, 2009;Masci, 2010Masci, , 2011a have recently put into question well-known magnetic seismogenic precursors by showing that these anomalous signals are actually induced by normal geomagnetic activity. Prattes et al (2011), hereafter cited as P11, report the analysis of ULF magnetic data coming from the South European Geomagnetic Array (SEGMA) during the period [2008][2009].…”