Retrospective investigation of geomagnetic field time-series during the 2009 L'Aquila seismic sequence

This paper reports the analyses of ULF (Ultra-Low-Frequency) geomagnetic field observations coming from the Geomagnetic Observatory of L'Aquila during the period 2008–2009. This period includes the L'Aquila 2009 seismic sequence, where the main shock of 6 April heavily damaged the medieval centre of the town and its surrounding area, causing 308 deaths, more than 1000 injuries and about 60,000 displaced people. Recently, several publications have documented the observation of precursory signals which occurred before the 6 April earthquake (e.g. Eftaxias et al., 2009, 2010), while others do not find any pre-earthquake anomaly (e.g. Villante et al., 2010; Di Lorenzo et al., 2011). In light of this, the goal of this study is to carry out further retrospective investigations. ULF magnetic field data are investigated by means of conventional analyses of magnetic polarization ratio, improved magnetic polarization ratio, and fractal analysis. In addition, total geomagnetic field data coming from the INGV Central Italy tectonomagnetic network have also been investigated, using the simple inter-station differentiation method. Within the limits of these methods, no magnetic anomalous signal which may be reasonably characterized as a precursor of the L'Aquila earthquakes has been found