Some aspects of global earthquakes: Investigation of earthquakes source parameters in different seismic zones

SUMMARY In this study, several catalogs of global earthquakes have been compiled to examine some aspects of global earthquakes and the effects of different tectonic structures on the source parameters. For this purpose, the world was divided into 28 different seismic regions. Some empirical relations were developed for various source parameters of shallow earthquakes and the results obtained were compared with the previous studies published in literature. The empirical relations developed were discussed in terms of the types of faulting and tectonism. Relations between stress drop, Act, and moment/ magnitude, Mf/Mg, were investigated for different fault types and different seismic sources. The results show that source functions of large strike-slip, normal and reverse faults with strike-slip component are complex. The other types of faulting are simple. Also, the complex earthquakes are associated with subduction zones with old lithosphere while simple earthquakes are associated with subduction zones with young lithosphere. Energy magnitude, Me, is higher than moment magnitude, Mw, for complex earthquakes. Average high seismic energy is observed for strike-slip faults while average high seismic moment is observed for reverse faults. It is also found that average apparent stress of strike-slip faults is relatively higher than that of the other fault types. Generally, magnitude of ME for strike-slip faults and magnitudes of Mw for reverse faults are higher than the other fault types. The average apparent stress for earthquakes with Mg>Mw is 1 1 times higher than earthquakes with M^Mg. High values of apparent stress were observed on oceanic transform faults and low values were observed on thrust faults associated with subduction zones. Average stress drop of complex earthquakes is about 4 times higher than that of simple earthquakes. High stress drops are related to strike-slip faults and earthquakes from subduction zones with old lithosphere. Key Words: Magnitude, Focal Mechanism, Seismic Energy, Seismic Moment, Apparent Stress, Stress Drop VI