Late Cenozoic Faults of the Region Surrounding the Eagle Flat Study Area, Northwestern Trans-Pecos Texas

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The Eagle Flat study area is located along the southeastern edge of the southern Basin and Range-Rio Grande tectonic province in Trans-Pecos Texas. The desert region that encompasses the study area consists of the broad Diablo Plateau and a series of mountain ranges and adjacent intermontane basins that formed by extensional faulting that probably occurred in the last 24 mya. There has been no historical surface rupturing of faults in Trans-Pecos Texas, although earthquakes have occurred and faults that displace Quaternary (present to approximately 2 mya) deposits are present (fig. 1). Geologic investigations of faults active during the Quaternary provide important data (tables A-1 and A-2) for seismic risk studies of the proposed Eagle Flat low-level radioactive waste repository. Most of the Quaternary faults of Trans-Pecos Texas are between about 11 and 24.8 mi (18 and 40 km) long (table A-1). Many of the faults are sections of longer fault zones that are between 43 and 64 mi (70 and 105 km) long. Strikes of individual faults are variable, although most of the fault zones strike northwestward or northward. Faults dip between 50° and 89°. Fourteen Quaternary faults are within 31 mi (50 km) of the proposed repository.


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