Discrimination Between Small Earthquakes and Quarry Blasts in Egypt Using Spectral Source Characteristics

Abstract

AbstractSource parameters calculated from displacement spectra of both P and S waves are used to discriminate between earthquakes and quarry blasts in three regions of Egypt during the 2009–2015 period. We use vertical component seismograms from 440 earthquakes and 450 quarry explosions with MD 1.5 to 3.3 to calculate source parameters, including scalar moments and corner frequencies. The Mo(P,S) vs. fc(P,S) and P- to S-wave corner frequency fc(P)/fc(S) ratios are used to distinguish quarry blasts from earthquakes. A comparison of Mo(P,S) vs. fc(P,S) for both earthquakes and explosions in Egypt demonstrates that explosions had significantly lower corner frequencies than earthquakes, particularly for S-wave displacement spectra. In contrast to the Northern and Central regions, the Southern Egyptian region provides a perfect separation of corner frequencies of earthquakes and explosions for both P- and S-waves. The empirically derived average ratio of fc(P)/fc(S) for earthquakes is 1.28, 1.26 and 1.26 in the Northern, Central and Southern Egyptian regions, respectively. For explosions, average fc(P)/fc(S) ratios are 1.89, 1.86 and 2.0 in the three Egyptian regions, respectively. According to these findings, the average ratio of fc(P) to fc(S) for explosions is higher than those for earthquakes, implying that the differences in ratios enhance the ability of the fc(P) vs. fc(S) approach to discriminate between earthquakes and explosions. Based on the average fc(P)/fc(S) ratios vs. Mw in the whole of Egypt, the observed fc(P)/fc(S) discrimination threshold value for separating quarry explosions from earthquakes is 1.51–1.52.