Focal Mechanism Dependence of a Few Seismic Phenomena and its Implications for the Physics of Earthquakes

We studied the scaling of reduced energy versus seismic moment, the Coulomb stress triggering, and the property of clustering for global shallow earthquakes with different focal mechanisms. Clear focal mechanism dependence can be observed for these three phenomena. For strike-slip earthquakes, reduced energy increases slightly, nearly constant with the increase of seismic moment, while for thrust and normal earthquakes, reduced energy decreases with seismic moment. The level of reduced energy for thrust and normal earthquakes is several times smaller than that for strike-slip earthquakes. Thrust earthquakes exhibit clear stress triggering effect, strike-slip earthquakes possess almost no such a property, while normal faulting type earthquakes lie in between. Thrust earthquakes are more likely to occur in ‘pairs’ or ‘groups’, while strike-slip earthquakes are more likely to be ‘single’. These three phenomena are related to each other in the physics of earthquakes.