Earthquakes and seismicity of the Grand Canyon region

The seismicity of the Grand Canyon region of northern Arizona is contiguous with the Intermountain Seismic Belt of Utah. This, plus a similar recurrence rate north of the canyon (and a common style of faulting), suggests that the seismicity of the Grand Canyon region represents an extension of the Intermountain Seismic Belt of Utah. An analysis of the distribution of epicenters indicates that the majority of the events are concentrated in a rather narrow, northwest-trending band between the Mesa Butte and the West Kaibab fracture systems. This trend of activity, plus the northwestern trend of potential fault planes from the 7/4/81 event and one from the 8/31/83 event, suggest that it is the northwest-trending fracture systems, such as the Grandview-Phantom, which contain presently active faults. It seems likely that the seismicity of the Grand Canyon region is an expression of a tectonic boundary that is marked by a change in structural style as well as in crustal thickening. This seismicity is the product of an active stretching or extension of the crust. If this extension continues to affect the crust of the Colorado Plateau in the future, the tectonic boundary will continue to migrate into the interior of the plateau - eventually leaving the Grand Canyon region a seismically quiet area. -from Author