GNGTS 2021 - Atti del 39° Convegno Nazionale

195 GNGTS 2021 S essione 2.1 for Extremely Low and Ultra Low frequencies (0.001 to 100 Hz) magnetic fluctuation events ( MF ) at ground stations (Schekotov et al., 2006; Hattori et al., 2010). The Japanese and Kamchatka studies obtained correlations with time differences of 2 - 5 days before seismic events, and probability gains G MF = 1.6 (Han et al., 2014) to G MF = 2.6 (Hayakawa et al., 2019) were reported. Following the work by Console (2001), the prediction related to the detection of a precursor consists of the earthquake event occurrence of minimal magnitude in the alarm volume. In this framework, the performance of a specific method is carried out through the statistical parameters that can be evaluated in the case of NOAA data, such as the success rate N S / N A , the false alarm rate (N A – N S ) / N A , the alarm rate N S / N E , the failure rate (N E – N S ) / N E , and the probability gain is defined as G = N S / (N A V A ) / (N E / V T ) , (1) where N S is the success number, N A is the alarm number that is the electron burst number, N E is the earthquake number, V A is the alarm volume, and V T is the total volume represented in the scenario of Figure 1. In this representation, the precursor volume is indicated by V P . Note that this description is completely equivalent to those presented in Fidani (2018) being N S = max Δt [Σ {EQ;EB} (EQ × EB)] , V A = A·N h , where A is the Indonesian and Philippine areas, and V A = A being the alarm duration of one hour. V A by NOAA particle data is constant for all the alarms. Thus, the success rate is exactly P(EQ|EB) , the false alarm rate is 1 – P(EQ|EB) , the alarm rate is max Δt [Σ {EQ;EB} (EQ × EB)]/N E , the failure rate is 1 – max Δt [Σ {EQ;EB} (EQ × EB)]/N E , and the probability gain due to electron burst detections G EB = P Δt (EQ|EB)/P(EQ) = 1 + corr Δt {(EQ,EB)√[1/P(EQ) – 1][1/P(EB) – 1]} 1/2 , (2) where corr Δt (EQ,EB) is the particular correlation and P Δt (EQ|EB) is the particular conditional probability both corresponding to Δt of 2 - 3 hours. G EB is about 3 for the earthquake epicenter altitude projection of 2,000 km. The condition of independent candidate precursors is difficult to prove, and a set of physical links for a part of them is suspected, see for example Pulinets et al., (2015). Therefore, it seems that dependent candidate precursors represent the most common occurrence. Therein, the conditional probability of an earthquake with a magnitude greater than M is not increased by a simple product of a further probability gain of another detected precursor (Aki, 1983), if this Fig. 2 - A comparison of magnetic induction lines produced by the rectangular and circular sections in the center of top right; continuous lines are generated by the rectangular strip (s), whereas the dotted lines are generated by the wire (w). B dependence, from the distance d at half of the stripe width of the currents are shown on the plot for both conductors infinitely long or of length L .