10/13/2017 - 3:30pm
Title: Global Variations of Large Megathrust Earthquake Rupture Characteristics
Rupture characteristics of large earthquakes on subduction zone plate boundary faults vary substantially. The asperity model, proposed in the early 1980s, related regional variations of the largest earthquake size and overall rupture complexity to variations in stress heterogeneity. Repeating earthquakes, geodetic measurements of inter-seismic strain accumulation, and numerical modeling support the notion of frictionally locked asperities surrounded by creeping regions with different frictional properties. Yet, the fundamental nature of asperities has remained elusive for decades; the basic question is whether similar size slip patches (asperities) in different regions have similar dynamic rupture characteristics. Determining static slip distributions alone cannot resolve this issue; nor can static stress drop. Given the profoundly different rupture processes between events such as the 2004 Sumatra and 2011 Tohoku earthquakes, we need a sensitive measure of earthquake complexity that allows us to detect any regional systematics not apparent in standard measurements. We introduce a new non-dimensional source parameter, the radiated energy enhancement factor (REEF), the ratio of the directly measured broadband radiated energy to the calculated minimum radiated energy for given seismic moment and source duration. For 119 large megathrust events, we find that REEF values vary regionally, reflecting the variation of asperity properties of each subduction-zone boundary. Segmentation, roughness, fluid distribution, and tectonic loading in the subduction zone may be responsible for such variations. For each region, fluctuations in REEF result from multiple patch interaction and triggering. Thus, determination of REEF can better represent the rupture characteristics of great earthquakes.
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