GNGTS 2014 - Atti del 33° Convegno Nazionale

32 GNGTS 2014 S essione 2.1 America. Earthquakes occurred principally in the sea, which was in contrast with previous results (Sgrigna et al. , 2005) and in agreement with past electromagnetic results (Nemec et al. , 2009). The epicentre positions of all these earthquakes were located in the positions where the more frequent strong seismic events occurred during the studied period. These earthquake positions were also causally physically linked with electron perturbations occurring several hours before the main shocks which were located west of detection positions. In fact, when perturbations of electron trapped conditions occurred at earthquake projection altitudes, they could have changed both electron pitch angles and bouncing altitudes at locations westwards of South Atlantic Anomaly. Furthermore, NOAAMEPED were sensitive to much lower energies, compared to previous studies: between 30 keV and 100 keV compared to several MeV. This latter observation suggests that the drift velocity of detected electrons will be generally lower than previous cases. Its corresponding electron drift periods were calculated using the expression: T d = (1.05/ E (MeV) L )*1/(1+0.43 sin�α eq ). ���(1) For 30 keV and 100 keV, the results from Eq. (1) were 21 hours and 6 hours, respectively. Moreover, detector energy band modifications due to degradation were considered to have the effect of increasing the detection energy intervals of about 30 keV (Evans et al. , 2008). Being electron bursts which contributed to the correlation in late years, when increasing detection energy taken plays, the drift periods from Eq. (1) were calculated to be 10.5 hours and 4.5 hours, respectively. These electrons belonged to the low L -shell range of 1.15 < L < 1.35, as in past works. The electrons which produced the correlation met satellite vertical detectors in the drift loss cone near the South Atlantic Anomaly about 2 - 3 hours before the earthquake time, after having drifted eastwards. This means that the perturbations had to have started much earlier. In fact, it was calculated that an earlier time between 1.5 – 3.5 hours was necessary for electrons to cover about 120° which divided earthquake epicentre longitudes of Sumatra and The Philippines from the detection area; with the electrons moving eastwards at drift velocity Fig. 3 – The altitudes of mirror points for electrons at L = 1.2 are indicated compared to NOAA-15 and atmosphere altitudes. Coloured areas indicate altitude/longitude regions where there are bouncing points of electrons that are detectable by NOAA-15 satellite. Yellow and sky-blue areas are relative to the Southern and Northern Hemispheres, respectively; the green area is the shared area. The red and orange areas are the more frequent possible interaction areas between earthquakes and electron bursts. The South Atlantic Anomaly is delimited by vertical lines.