THE DISCRIMINATION BETWEEN NATURAL EARTHQUAKES AND ARTIFICIAL EXPLOSIONS AROUND THE GREATER CAIRO AREA, EGYPT

Abstract

It is found that, there are many industrial cement factories have been distributed in and around the Greater Cairo area. These cement factories use big quantities of dynamites to generate seismic energy, that affect the new cities constructed recently in and around the Greater Cairo. It is also shown that, some microearthquake activities have been recorded by the Egyptian National Seismograph Network (ENSN). Therefore, it was very important to discriminate between the natural earthquakes and artificial explosions. In this study, about 163 quarry blasts and 125 local earthquakes around the Greater Cairo were monitored by the ENSN. The discrimination tools, that have been used in this study, are: the polarities of the first arrivals, the features of the seismograms, the spectral analysis of the waveform, the focal depth distributions, and the geographical distribution of the epicenters. It is observed that, the polarities of the first arrivals of the quarry blasts are usually up, while the polarities of the microearthquakes are varying from up to down. The local earthquakes have maximum values of energy ranging from –135 dB to –95 dB at higher frequencies, but the energy content has minimum values varying from –145 dB to –100 dB at low frequency range. For the quarry blasts, the energy content decreases by increasing the frequencies ranging from –170 dB to –100 dB at high frequency range, but the energy content at lower frequencies ranges from –160 dB to –100 dB. For the focal depth, the quarry blasts have shallower focal depths less than 100 meters, but the natural earthquakes have relatively deeper focal depths starting from 3.3 km. The geographical distribution of the epicenters of local earthquakes is concentrated at the high seismic active areas, but the quarry blasts epicenters are located around the quarries of the cement factories in and around the Greater Cairo area.