Structural and seismic data for the eastern Grand Canyon were analyzed to determine the relationship between basement fractures, surface faulting, and seismicity. Published structural data were compared with the results of focal mechanism analysis of tremors occurring in the eastern canyon region during the period 1989–2004. Previous studies of the geology of this area indicate that the fault and joint trends exposed in the surface rocks and through the entire sedimentary section were first established with predominant northeast and northwest trends in Precambrian time. The northwest trends of this prefractured terrane correlate with a dominant northwest trend of nodal planes in the seismic data, suggesting that the present stress system in the region is favoring the reactivation of the preferentially oriented pre-existing northwest-trending fractures.

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