Near-Source Released Energy in Relation to Fracture Energy on Earthquake Faults

The near-source energy released on a fault is estimated through the strain energy change and the fracture energy from the results of kinematic waveform inversion and dynamic modeling for two different types of earthquakes: a shallow crustal earthquake, the 2000 Tottori, Japan (Mw 6.6) earthquake, and an in-slab event, the 1999 Oaxaca, Mexico (Mw 7.5) earthquake. The procedure incorporates the spatial distribution of slip, critical slip-weakening distance, stress drop, and strength excess. The results show that the near-source energy density estimated over major asperities on the fault is nearly the same for the two earthquakes, while the fracture energy on the in-slab fault is appreciably larger than that for the crustal fault, suggesting higher strength in the in-slab fault zone. The near-source released energy on major asperities is significantly larger than the fracture energy in the two earthquakes.