AUTOMATON MODELS OF SEISMIC FRACTURE - CONSTRAINTS IMPOSED BY THE MAGNITUDE-FREQUENCY RELATION

To obtain an understanding of the ingredients required in a realistic model of fa t dynamics, we have constructed a number of models for the initiation and propagation of seismic fractures on a planar fault. Th e models are all of the cellular automaton-type and fall into two broa d categories which can be subdivided into 40 different classes. They d iffer in whether the fracture propagates as a crack or as a partial st ress drop model; whether they are loaded homogenously or randomly; whe ther or not the models are asperity models; whether the characteristic time associated to the initiation of fracture is short or long; and w hether or not the dynamic variable (e.g., stress or energy) is conserv ed on the fault plane. We restrict ourselves to the question whether m odels are capable of reproducing a Gutenberg-Richter power-law decay o f event frequency with fracture dimensions, irrespective of the b valu e. We find that very few models can generate a power law which extends to all sizes, although more models can generate power laws that cover a broad range of sizes. Of these, only a few exhibit acceptable scali ng behavior with system size. We conclude that, within the class of mo dels studied, only a reduced subset of partial stress drop models is a cceptable for the modeling of seismic fault dynamics.