Abstract

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 () may be determined with formal errors of similar to 30%, similar to 12%, and similar to 10%, respectively. In contrast, derived parameters such as the radiated energy (E-r), the radiation efficiency ((r)), and the fracture energy (G) have larger errors, around similar to 70%, similar to 40%, and similar to 25%, respectively. We applied the method to the M-w 6.5 intermediate-depth (62km) normal-faulting earthquake of 11 December 2011 in Guerrero, Mexico. Inferred values of =29.26.2MPa and (r)=0.260.1 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=(14.43.5)x10(14)J), producing a slow rupture process (V-r/V-S=0.470.09) despite the relatively high energy radiation (E-r=(0.54 +/- 0.31)x10(15)J) and energy-moment ratio (E-r/M-0=5.7x10(-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. Key Points New method for imaging the earthquakes source dynamicsFundamental source parameters of an intermediate-depth Mexican earthquakeSlow rupture, low radiation efficiency, high stress drop, and small rupture area AU1GH 119 (10): 7768-7785 OCT 2014 606 SLIP-WEAKENING DISTANCE SPONTANEOUS RUPTURE INSLAB EARTHQUAKES FRACTURE ENERGY FAULT VELOCITY STRESS MOTION SUBDUCTION ZONE Cruz-Atienza, Victor Manuel Cruz-Atienza, Victor Manuel Victor Manuel Cruz-Atienza Iglesias, Arturo Iglesias, Arturo Arturo Iglesias Madariaga, Raul Madariaga, Raul Raul Madariaga