The mechanisms generating the charges/potentials and abnormal electromagnetic radiation that accompany earthquakes have been discussed based on observational, theoretical and laboratory studies, in particular over the last few decades. We previously conducted stick-slip tests using precut granite cores with a contact electrode on the sample side, and proposed that surface charges released from charge trapping centres on sheared asperities are a possible source of the above-mentioned charges or potentials. Here we discuss seismoelectric and magnetic fields formed by the surface charges, and derive their scaling laws with the earthquake magnitude at a distance. According to our model, detectability of these fields at a point on the ground surface depends strongly on wet/dry condition at a fault zone (sheared asperities).
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