The 6 April 2009 earthquake at L'Aquila: a preliminary analysis of magnetic field measurements
Natural Hazards and Earth System Sciences
Several investigations reported the possible identification of anomalous geomagnetic field signals prior to earthquake occurrence. In the ULF frequency range, candidates for precursory signatures have been proposed in the increase in the noise background and polarization parameter (i.e. the ratio between the amplitude/power of the vertical component and that one of the horizontal component), in the changing characteristics of the slope of the power spectrum and fractal dimension, in the
... ion, in the possible occurrence of short duration pulses. We conducted, with conventional techniques of data processing, a preliminary analysis of the magnetic field observations performed at L'Aquila during three months preceding the 6 April 2009 earthquake, focusing attention on the possible occurrence of features similar to those identified in previous events. Within the limits of this analysis, we do not find compelling evidence for any of the features which have been proposed as earthquake precursors: indeed, most of aspects of our observations (which, in some cases, appear consistent with previous findings) might be interpreted in terms of the general magnetospheric conditions and/or of different sources. -A substantial increase in the noise background starting from days to several weeks preceding earthquake covering almost the entire ULF range (Loma Prieta, Spitak, Guam, Alum Rock), followed by an anomalous dip in the range 0.2-5 Hz starting one day ahead the earthquake (Loma Prieta). -An increase to a high level of activity in the range ≈10-50 mHz starting few hours before the earthquake (Loma Prieta, Spitak). -A broad maximum of the "polarization parameter" R 2 =P Z /P H about one month before the earthquake (P Z and P H being the integrated power of the vertical component, Z, and of the North/South component, H, in the Published by Copernicus Publications on behalf of the European Geosciences Union.