GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 2.1 343 Fig. 1 - The position of the loop for the magnetic detector installed at Chieti Station with respect to the epicentres of Central Italy seismic events in 2016-2017. when a strong earthquake struck Norcia. Daily numbers of pulses continued to increase up until November 3, reaching a peak of 94 counts. There was no evidence of daily pulse number increases around the Amatrice main event on August 24, 2016. Unfortunately, data was not available for the week prior this event. There was evidence of daily pulse number increases from both the analysis around the Capitignagno seismic swarm which manifested four strong earthquakes with magnitudes between 5.0 and 5.7 on January 18, 2017. Increases in pulse numbers began on January 17, 2017, and reached a maximum on January 19, 2017. Contemporary recordings of electric detectors operating at the same location in Chieti did not evidence correspondent pulses of the electric fields to those of the magnetic field (Fidani, 2017), this limited the maximum intensity of magnetic pulse. Magnetic pulse detected intensities were relevant being of the order of μT. Given that, recent experiments produced smaller intensities for magnetic pulses recorded during seismic activity, a test was build to verify this result by a coupled loop where electrical currents were controlled, see Figure 2. The magnetic field that was produced by a circular loop of radius R and that was coupled with the Chieti loop can be calculated (Landau and Lifsits 1986) B = 2J[K+E(R 2 -r 2 -x 2 ) / ((R-r) 2 +x 2 )] / [c((R+r) 2 +x 2 )] where J is the electric current density, K and E are the elliptical integrals, r and x are the distances from the axis and from the loop plain, respectively. This test confirmed the intensity of recorded pulses. Several physical models were used to obtain measured intensities of magnetic pulses. To have an initial estimate of the minimal electrical current flowing in the earth’s crust, a simple model was thought by the Biot-Savart law which considers an infinitely long line conductor, see Figure 3 left, that is at some depth in the earth’s crust. Then |B| = μo |I|/(2 π r). Fig. 2 - Schematic of a couple of loops where a well known electric current in a loop was used to set the magnetic sensibility of the other loop.