09:30 〜 09:45
[S13-5-05] Dynamic Source Inversion of Intermediate Depth Earthquakes in Mexico
The source mechanisms of earthquakes at intermediate depth (50-300 km) are still under debate. Due to the high confining pressure at depths below 50 km, rocks ought to deform by ductile flow rather than brittle failure. Several source mechanisms have been proposed, but for neither of them conclusive evidence has been found. One viable mechanism is Dehydration Embrittlement, where liberation of water lowers the effective pressure and enables brittle fracture. Another is Thermal Runaway, a highly localized ductile deformation. In the Mexican subduction zone, intermediate depth earthquakes represent a real hazard in central Mexico due to their proximity to highly populated areas and the large ground accelerations.
To improve our understanding of these rupture processes, we use a recently introduced inversion method to analyze several intermediate depth earthquakes in Mexico. The method inverts strong motion seismograms to determine the dynamic source parameters based on a genetic algorithm. It has been successfully used for the M6.5 Zumpango earthquake (62 km depth). For this event, high radiated energy, low radiation efficiency and low rupture velocity were determined. This indicates a highly dissipative rupture process, suggesting that Thermal Runaway could probably be the dominant source process.
In this work we improved the inversion method by introducing a theoretical consideration for the nucleation process that minimizes the effects of rupture initiation and guarantees self-sustained rupture propagation. Preliminary results indicate that intermediate depth earthquakes in central Mexico may vary in their rupture process. For instance, for a M5.9 earthquake at 55 km depth that produced very high accelerations in Mexico City we found a moderate radiation efficiency and a typical rupture velocity. Differences and similarities between the earthquakes studied here will help to better elucidate the physical processes originating intermediate depth earthquakes.
To improve our understanding of these rupture processes, we use a recently introduced inversion method to analyze several intermediate depth earthquakes in Mexico. The method inverts strong motion seismograms to determine the dynamic source parameters based on a genetic algorithm. It has been successfully used for the M6.5 Zumpango earthquake (62 km depth). For this event, high radiated energy, low radiation efficiency and low rupture velocity were determined. This indicates a highly dissipative rupture process, suggesting that Thermal Runaway could probably be the dominant source process.
In this work we improved the inversion method by introducing a theoretical consideration for the nucleation process that minimizes the effects of rupture initiation and guarantees self-sustained rupture propagation. Preliminary results indicate that intermediate depth earthquakes in central Mexico may vary in their rupture process. For instance, for a M5.9 earthquake at 55 km depth that produced very high accelerations in Mexico City we found a moderate radiation efficiency and a typical rupture velocity. Differences and similarities between the earthquakes studied here will help to better elucidate the physical processes originating intermediate depth earthquakes.