On Scaling of Fracture Energy and Stress Drop in Dynamic Rupture Models: Consequences for Near-Source Ground-Motions

We calculate spontaneous dynamic rupture models for several well-recorded moderate to large earthquakes and analyze the scaling properties of fracture energy and stress drop. Among the set of 12 source models for 9 different earthquakes, the large events did break the surface while the moderate-size events occurred as completely buried ruptures (i.e. no surface faulting). We find that dynamic and static stress drop differ by only about 10%. Fault-averaged stress drop increases with increasing earthquake magnitude, while also fault-averaged (or maximum) fracture energy grows with magnitude. The scaling of fracture energy with the stress intensity factor appears to be sensitive to whether or not the earthquake rupture broke the surface, indicating that large earthquakes consume more fracture energy as the rupture expands and reaches the surface. This scaling of fracture energy may shed light on the recent observation that large, surface breaking earthquakes apparently generate lower near-source ground motions than buried ruptures in a certain period range of engineering interest. The derived empirical scaling relations for fracture energy may help to constrain the initial conditions for future dynamic rupture modeling, but can also be used in physics-based source characterization for near-source groundmotion calculations.