Space-time analysis of observed and modeled aftershock sequences

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Extreme earthquakes can generate tens of thousands of aftershocks in a relaxation process that is not understood. The rate of aftershocks decays as a power law in time (Omori’s Law), similar to the time-invariant decay rates observed following other extreme phenomena. If the mechanisms driving aftershocks can be determined using physical arguments and numerical models to compare with vast datasets of aftershock patterns, then significant advances will be made in understanding earthquakes and their extreme limits. A current hypothesis for aftershock generation results from post-seismic degassing of trapped high pressure sources at depth. In this scenario, the ensuing pressure pulse 'invades' the overlying crust that should produce complex tree-like structures along flow paths that should be discernible in aftershock catalogs. The purpose of this proposal is to search for, quantify, and model such structures. We propose to analyze in detail the time evolution of 3-dimensional aftershock patterns from a variety of tectonic environments to evaluate whether observed patterns are indicative of fluid-pressure-induced aftershocks. This will require nonlinear space time pattern analyses and the development of new algorithms to visualize and model this scenario. Specifically, we will 1) develop visualization techniques to study the space-time evolution of aftershock sequences, 2) quantify the evolution of aftershocks by identifying the hypothesized underlying network structure, 3) develop 3- dimensional numerical models that include the dominant physical and chemical processes acting, and 4) make detailed comparisons between model results and aftershock observations.