Correlations between earthquakes and anomalous particle bursts from SAMPEX/PET satellite observations

In the last decades, a possible influence of electromagnetic fields of seismic origin in the ionosphere-magnetosphere transition region has been reported in the literature. In recent years, a few space experiments also revealed anomalous bursts of charged particles precipitating from the lower boundary of the inner radiation belt. They were thought to be caused by low-frequency seismo-electromagnetic emissions. A recent study [Aleksandrin et al., 2003. Annales Geophysicae 21, 597-602] seems to confirm that these particle bursts have a short-term preseismic character. The particle longitudinal drift should enhance the detectability of preseismic particle bursts, thus magnifying their importance in earthquake prediction studies. This paper takes into consideration the method introduced by Aleksandrin et al. (2003) to carry out a deeper investigation on the subject. In this sense, a method for the temporal correlation between continental earthquakes with M⩾5.0 and anomalous particle bursts collected by the PET-SAMPEX satellite mission is critically investigated and presented here. Several constraints and cuts have been applied to data in order to exclude, from the correlation, charged particles collected inside the SAA region and/or during ionospheric and magnetospheric perturbations caused by non-seismic sources. After the data have been detrended by these effects, a short-term seismic precursor of ∼4 h is observed in the histogram of the time difference between the time occurrence of earthquakes and that of particle burst events. The best correlation is obtained only when considering high-energy electrons (E⩾4MeV) with pitch angles near the loss cone. Such a result confirms previous ones but also points out the importance of an ad hoc method of analysis. Results suggest the importance of coordinated and simultaneous ground-based and space investigations specifically dedicated to the subject. Also, a deeper investigation based on particle data prepared and analyzed as carefully as possible is requested to understand the physical mechanisms underlying the phenomenon under study.