Publication Date:
2014-09-28
Description:
We introduce a method for imaging the earthquake source dynamics from the inversion of ground-motion records based on a parallel genetic algorithm. The source model follows an elliptical patch approach and uses the staggered-grid split-node method to simulate the earthquake dynamics. A statistical analysis is used to estimate errors in both inverted and derived source parameters. Synthetic inversion tests reveal that the average rupture speed ( V r ), the rupture area and the stress drop (Δτ) may be determined with formal errors of ~30%, ~12% and ~10%, respectively. In contrast, derived parameters such as the radiated energy ( E r ), the radiation efficiency ( η r ) and the fracture energy ( G ) have larger errors, around ~70%, ~40% and ~25%, respectively. We applied the method to the Mw6.5 intermediate-depth (62 km) normal-faulting earthquake of December 11, 2011 in Guerrero, Mexico. Inferred values of Δτ = 29.2 ± 6.2 PMa and η r = 0.26 ± 0.1 are significantly higher and lower, respectively, than those of typical subduction thrust events. Fracture energy is large, so that more than 73% of the available potential energy for the dynamic process of faulting was deposited in the focal region (i.e. G = (14.4 ± 3.5) × 10 14 J), producing a slow rupture process ( V r / V S = 0.47 ± 0.09) despite the relatively-high energy radiation ( E r = (0.54 ± 0.31) × 10 15 J) and energy-moment ratio ( E r / M 0 = 5.7 × 10 − 5 ). It is interesting to point out that such a slow and inefficient rupture along with the large stress drop in a small focal region are features also observed in both the 1994 deep Bolivian earthquake and the seismicity of the intermediate-depth Bucaramanga nest.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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