[S13-3] Earthquake source mechanics III

[S13-3-04] Radiated Energy Enhancement and Rupture Complexity of Large Subduction-Zone Earthquakes

Lingling Ye¹, Hiroo Kanamori¹, ^○Thorne Lay² (1.California Institute of Technology, CA, US, 2.University of California at Santa Cruz, CA, US)

The rupture characteristics of large earthquakes on subduction zone plate boundaries vary substantially. The asperity model, proposed in the early 1980s, related variations of the largest earthquake size and complexity in a region to stress heterogeneity. Repeating earthquakes and geodetic measurements of inter-seismic strain accumulation support the notion of asperities being surrounded by creeping regions with different frictional properties. The surge of large earthquakes over last decade and the advance in observations and analysis techniques allow us to evaluate whether asperities differ from region to region. To quantify variable rupture complexity, we introduce a new energy radiation parameter, the radiated energy enhancement factor (REEF): the ratio of directly measured broadband radiated energy to the calculated minimum radiated energy for an event of equal seismic moment and duration with parabolic shape moment-rate function). For large earthquakes, REEF is closely related with complexity in the observed moment-rate function. We find that (1) REEF variation among different subduction zones is consistent with the level of segmentation proposed in the asperity model; and (2) REEF values are similar for earthquakes with different magnitudes in each region. Both observations indicate that the regional “asperity" structure observed at scales of tens to hundreds of kilometers is similar to that at smaller scales. Asperities thus differ from region to region, likely due to variable stress conditions on the plate boundaries.