Appendix I

This report presents the results of a reconnaissance analysis of Quaternary faulting in central Arizona, conducted for the U.S. Bureau of Reclamation. The goal of this study has been to thoroughly delineate locations of possible Quaternary faulting in the area surrounding existing and potential dam sites in central Arizona.

Probable quaternary faults in Arizona have been mapped by systematic interpretation of aerial photographs, extensive geomorphic field studies, and compilation of previous work. Greatest concentrations of late Quaternary normal faults are found near the Colorado Plateau margin in northwestern and north-central Arizona, with lesser concentrations in central and southeastern Arizona and the Lake Mead area. Late Quaternary faults are rare in southwestern Arizona and none have been recognized in the interior of the Colorado Plateau province in northeastern Arizona.

The Tucson 1 ° X 2.0 quadrangle exhibits a wide variety of basin landforms and late Cenozoic surficial geologic deposits. Several factors contribute to this diversity. The Tucson quadrangle spans the transition between the relatively low ranges and typically undissected basins of south-central Arizona and the higher ranges and typically dissected basins of southeastern Arizona.

This report is a compilation of available data on Quaternary faults in Arizona as of the summer of 1998. These data were compiled as part of a effort to compile data and map information on Quaternary faults throughout the world, which is being overseen by Michael Machette of the U.S. Geological Survey.

The Colorado Plateau is a major tectonic and physiographic province in the southwestern United States which has been relatively stable during the Phanerozoic, but has been epeirogenically uplifted about 2 km in the Cenozoic.

The frequency of occurrence of earthquakes with different seismic moments is expressed in terms of the rate of slip on a fault and to the largest seismic moment likely to occur in the region.

A distinctive suite of volcanic, sedimentary, structural, and physiographic characteristics permits differentiation of the post-1 2- to 15- Ma Basin-Range disturbance from earlier mid-Tertiary extensional tectonism in Arizona. Basin-Range volcanism comprises basalts or bimodal basalt-rhyolite suites that are concentrated in several fields in central and northern Arizona; the age of volcanism generally decreases northeast and east onto the Colorado Plateau margin.

This map presents data and interpretations concerning the distribution, amounts and timing of neotectonic faulting in Arizona. It is one part of a larger study and analysis of the neotectonic framework of Arizona..

We present tectonic reconstructions and an accompanying animation of deformation across the North America–Pacific plate boundary since 36 Ma.

We develop recommendations for design spectra at two sites, one in the Mojave desert, California, and the second at Columbia, South Carolina. These sites were chosen because local, small earthquakes dominate the high frequencies (f⩾10 Hz), but large distant events dominate the low frequencies (f⩽1 Hz).


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