Systematic Characterization of Radiated Energy and Static Stress Drop of Global Subduction Earthquakes from Source Time Functions Analysis

Abstract:

Source Time Functions (STFs) describe how the seismic moment (Mo) is released with time. In addition to moment magnitude Mw, they carry information on more detailed rupture properties, such as static stress drop Δσ and radiated energy Er. Here we systematically analyze a set of 1500 STFs extracted from the SCARDEC method (Vallée et al 2011), containing the Mw>5.8, shallow (z<70 km) earthquakes with normal or inverse mechanisms that occurred in the past 20 years. At the global scale, we confirm the scale-invariance of Δσ with magnitude, while the apparent stress µEr/Mo slightly increases with seismic moment. In a second step, the source parameters distribution is investigated in light of the tectonic context of the earthquakes: we find that subduction interplate earthquakes have lower stress drop and apparent stress relative to all other earthquakes (e.g. crustal earthquakes), in agreement with other approaches (Houston, 2001; Allmann and Shearer, 2009). This observation may reflect the fact that subduction plate boundaries host a very large number of earthquakes, making the fault zone “mature”; or, it may be the consequence of the hydrated subducted materials leading to specific frictional properties. This finding may explain why damages observed after crustal earthquakes tend to be larger than the ones due to subduction earthquakes of the same magnitude. We finally focus on subduction interplate earthquakes (approximately 700 earthquakes) by considering 18 regional segments of subduction zones. We find that these segments do not have the same signature in terms of dynamic rupture properties, which means that large scale plate convergence properties influence rupture behavior. In a given segment, local heterogeneities of stress drop or radiated energy can be associated with local features of the subduction zone: in particular, we find that low coupled zones generate earthquakes with low stress drop and apparent stress.