GNGTS 2021 - Atti del 39° Convegno Nazionale

193 GNGTS 2021 S essione 2.1 FORECASTING PROBABILITY FOR STRONG EARTHQUAKES BY SINGLE AND MULTIPLE GEOPHYSICAL MEASUREMENTS ON THE EARTH’S SURFACE AND FROM SPACE Cristiano Fidani Central Italy Electromagnetic Network, Fermo, Italy Here, a contribution is presented which introduces the effect of a multiplicity of physical observations, both from space and from the ground, in order to evaluate the forecasting earthquake improvements that could be obtained. This approach refers to the correlation obtained between strong earthquakes and NOAA-15 polar satellite high energy electron bursts, and to the correlation obtained between strong earthquakes and magnetic pulses. The only further hypothesis is that both the observations are made in the same areas and during the same periods. Then, the improvements are calculated by a probability gain which is a combination of the single observation probability gains. NOAA polar satellites use particle detectors that monitor fluxes of electrons in polar orbits at altitudes between 807 and 854 km. Data can be downloaded at the link http://www.ngdc.noaa . gov/stp/satellite/poes/dataaccess.html. All of the sets of orbital parameters are provided every 8 seconds. Thus, 8-second averages of the electron counting rates, latitude, longitude data were calculated. Unreliable counting rates with negative values were labeled and excluded from the analysis. Since the energy detected for the electrons is a cumulative sum over three thresholds equal to E 1 = 30 keV, E 2 = 100 keV, and E 3 = 300 keV, new energy channels were derived from the difference of the energies thresholds to obtain electrons detected in the intervals 30 - 100 keV, 100 - 300 keV, and > 300 keV; which are more suitable for the dynamic analysis. To systematically test the methodology proposed for NOAA data, a quantitative and rigorous definition of the concerned precursor (Console, 2001) was defined. The daily averages of particle counting rates exiting the entrapment in the geomagnetic field were calculated, and then the condition for which a counting rate fluctuation was not likely, due to possible statistical fluctuations, was defined. This calculation was formulated with a probability larger than 99% (Fidani et al., 2010). The sudden increase in electron flux that satisfies this condition was named electron burst. According to previous work (Alexsandrin et al., 2003), the daily averages of counting rates were calculated in the invariant coordinate space. Together with the L -shell and the pitch angle, it was necessary to take into account the counting rate amplitudes and their variations versus geomagnetic coordinates, since the spatial gradient of particle fluxes near the South Atlantic Anomaly is too large. Counting rate distributions inside invariant volumes are compatible with a Poisson distribution. Being so, a threshold was introduced for the counting rates to define the conditions for which a counting rate is a non-Poissonian fluctuation with 99% probability. Moreover, NOAA satellites measure variations of ionospheric parameters are not only due to earthquakes but principally due to solar activity (Sgrigna et al., 2005). To reduce the effects of solar activity, both low values in Dst variations downloaded at the link http://wdc.kugi.kyoto-u.ac.jp/dst_final/index.html, and geomagnetic Ap indexes at the link ftp://ftp.ngdc.noaa.gov/STP/GEOMAGNETICDATA/APSTAR/ apindex, were chosen to exclude counting rate data corresponding to the sun influence (Fidani et al., 2012). The quantification of the precursor (Console, 2001) is obtained by the L -shell invariant parameter, which was considered to define a region of space where a physical interaction, whatever it is, can connect the seismic and ionospheric activities. Following works by Alexandrin et al., (2003), and Sgrigna et al., (2005), particle bursts were considered only when their L -shell values referred to well-defined intervals in altitudes above the M ≥ 6 earthquake epicenters. This is equivalent to imagining that the physical interaction can occur in the same region near the vertical. The correlation was calculated by filling a histogram with the time differences Δt