Dynamic Rupture and Source Properties in a Damage-Breakage Rheology Model

We present simulations of dynamic ruptures in a continuum damage-breakage rheological model, waves radiated by simulated sources, and synthetic seismograms observed in the far field. The damage-breakage model is based on irreversible thermodynamics of damage and breakage processes, and describes brittle instability as a phase transition in a process zone between damaged solid and granular material. The formulation significantly extends the ability to model brittle processes in structures with complex volumetric geometries and evolving properties, compared to the traditional models of frictional sliding on pre-existing surface(s) in a solid with fixed properties. The propagating rupture produces rock damage and granulation in the process zone ahead of the rupture front where significant local expansion-compaction occur, in addition to the large scale deviatoric deformation associated with the events. The co-seismic changes of rock properties within and behind the process zone significantly affect the radiation pattern from classical deviatoric results, including damage-related-radiation and enhanced isotropic components. The most pronounced feature is significant reduction of the S-wave amplitude radiated in the direction of the propagating rupture. The calculated Es/Ep seismic energy ratio is significantly lower (5-10) than predicted of standard models with no damage-breakage mechanism and no source volume components. We also present results on detailed comparisons between the simulated source properties and those obtained by analyzing the synthetic seismograms, and demonstrate the relations between different source processes and various seismic parameters (potency, stress drop, directivity, rupture velocity, corner frequency, and others). An explicit study of effects associated with complex dynamic rupture process, including realistic thickness of the fault core is an important advantage of the presented formulation compared to other dynamic earthquake rupture models assuming frictional surfaces.