Considerations on the global seismic sequences: the second and the third largest aftershocks

Abstract

Statistical considerations on the occurrence of the second largest aftershock of an earthquake sequence have been developed using global data. The time distribution of the second, M2, and the third, M3, largest aftershocks are studied here as well. The probability that these two aftershocks would occur in the first 24 hr after the main shock is more than 50 per cent. It was found that the second and the third largest aftershocks are distributed like the first largest aftershock. The difference, D2, is determined between the magnitudes of the main shock, M, and the second largest aftershock, M2, of an earthquake sequence. Using a complete data set, it was found that the difference, D2, has a mean of about 2.0. Two distinct cases of the M2 occurrence are observed. The first case (case 1) corresponds to normal aftershock sequence evolution, where M2 follows M1 (which is the largest aftershock of a sequence), while in the second one (case 2) M2 precedes M1. The values of the time distribution are totally different between case 1 and case 2. An attempt is made to interpret the temporal occurrence of the aftershocks, with respect to the surface (terrestrial) heat flow. The mean heat flow value for case 1 is qA= 1.61 ± 0.86, while for case 2 this is qB= 1.38 ± 0.82. It is shown that when the heat flow is high, the three largest aftershocks (M1, M2 and M3) temporally occur closer to the main shock.