The 6 April 2009 earthquake at L'Aquila: a preliminary analysis of magnetic field measurements

Abstract

Abstract. 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 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.

Ultra Low Frequency (ULF) European multi station magnetic field analysis before and during the 2009 earthquake at L'Aquila regarding regional geotechnical information

“…They occurred during the seismic active period. The classical polarization method has not shown an evidence of polarization events in relation to seismicity reported in Villante et al (2010). The SEGMA chain with multiple stations in various distances to L'Aquila gives the opportunity for further analysis.…”

“…Further, Villante et al (2010) performed a classical polarization analysis with magnetic field data recorded before and during the L'Aquila earthquake series 2009. In the present work we show results obtained with the improved standardized polarization method applied on recorded data at several geomagnetic stations belonging to the SEGMA network spread over mid-and south Europe in a time period of 15 months, including the strong seismic active and further seismic weak time periods in the area of L'Aquila.…”

On a reported effect in ionospheric TEC around the time of the 6 April 2009 L'Aquila earthquake

“…Because the Earth's crust is fluid saturated, Dahlgren et al (2014) conclude that significant electric currents are not expected to be generated the days before earthquakes during the slow stress accumulation in the region of earthquake nucleation; as a consequence no electric and magnetic signals are expected to be observed on the Earth's surface. Note that studies of data records from the L'Aquila area (see Biagi et al, 2010;Masci, 2012b;Masci and Di Persio, 2012;Masci and De Luca, 2013;Villante et al, 2010) have identified no anomalous magnetic or electric effects during the days or hours before and after the 6 April earthquake that might be hypothesized to have seismogenic origin. Still, in a recent report, Masci and Thomas (2016), by investigating magnetic field measurements from multiple magnetometers and seismic and strong motion records close to the earthquake epicentre, have shown that there is no evidence that might support the generation of an underground electric current in correspondence of the 6 April main shock, when the rupture occurred and the vast majority of mechanical energy was released.…”

On the man-made contamination on ULF measurements: evidence for disturbances related to an electrified DC railway

“…The epicenter of the strongest event was located ≈ 6.0 km from the geomagnetic observatory. An analysis of experimental measurements did not reveal any clear evidence for anomalous ULF signals preceding the earthquake's occurrence (Villante et al, 2010; see also Prattes et al, 2011;Nenovski et al, 2013); by contrast, possible coseismic magnetic effects were proposed by Di Lorenzo et al (2011). The city was suddenly evacuated, and all industrial plants, schools and public offices were closed; in the meanwhile, the civil protection and the emergency task and apparatus were all concentrated in the "Scuola Ispettori e Sovraintendenti della Guardia di Finanza" (≈ 1 km from the geomagnetic observatory) that also hosted the G8 summit on 8-10 July 2009.…”