DIFFUSIONLESS DILATANCY MODEL FOR EARTHQUAKE PRECURSORS

A dilatancy model without extensive pore fluid diffusion is proposed as an explanation for time-dependent geophysical anomalies occurring prior to earthquakes. As with the fluid flow models, the creation of thin dry or undersaturated cracks due to progressive distortion near the focal region is assumed. Rather than invoking fluid migration from the surrounding crust to fill cracks, the cracks are thought to close again before the earthquake because of decreasing stress levels imposed by strongly nonlinear constitutive properties of fault zone material. The proposed model and the fluid flow model predict qualitatively similar V-p/V-s, and resistivity histories. Whereas the fluid flow model predicts maximum epicentral uplift due to dilatancy at the time of the earthquake, the diffusionless model predicts uplift followed by subsidence prior to the earthquake, as well as premonitory creep in the focal region.