Deep resistivity structure of Yucca Flat, Nevada Test Site, Nevada

Asch, Theodore H.; Rodriguez, Brian D.; Sampson, Jay A.; Wallin, Erin L.; Williams, Jackie M.

doi:10.3133/ofr20061261

Cited by 5 publications

(1 citation statement)

References 3 publications

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“…Since 2003, the USGS has been conducting natural-source magnetotelluric (MT) surveys for the UGTA Sub-Project to better constrain pre-Tertiary stratigraphy and structures buried beneath thick sequences of alluvium and volcanic rocks. MT data from Yucca Flat proved particularly useful in constraining the extent and thickness of the upper clastic confining unit (UCCU) HSU beneath the basin (BN, 2006;Asch et al, 2006). This improved stratigraphic understanding led to a revised and better constrained structural model of the pre-Tertiary rocks beneath Yucca Flat.…”

Section: Geophysical Investigationsmentioning

confidence: 99%

A Hydrostratigraphic System for Modeling Groundwater Flow and Radionuclide Migration at the Corrective Action Unit Scale, Nevada Test Site and Surrounding Areas, Clark, Lincoln, and Nye Counties, Nevada

Prothro¹,

Drellack²,

Mercadante³

2009

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Underground Test Area (UGTA) corrective action unit (CAU) groundwater flow and contaminant transport models of the Nevada Test Site (NTS) and vicinity are built upon hydrostratigraphic framework models (HFMs) that utilize the hydrostratigraphic unit (HSU) as the fundamental modeling component. The delineation and three-dimensional (3-D) modeling of HSUs within the highly complex geologic terrain that is the NTS requires a hydrostratigraphic system that is internally consistent, yet flexible enough to account for overlapping model areas, varied geologic terrain, and the development of multiple alternative HFMs. The UGTA CAUscale hydrostratigraphic system builds on more than 50 years of geologic and hydrologic work in the NTS region. It includes 76 HSUs developed from nearly 300 stratigraphic units that span more than 570 million years of geologic time, and includes rock units as diverse as marine carbonate and siliciclastic rocks, granitic intrusives, rhyolitic lavas and ash-flow tuffs, and alluvial valley-fill deposits.The UGTA CAU-scale hydrostratigraphic system uses a geology-based approach and two-level classification scheme. The first, or lowest, level of the hydrostratigraphic system is the hydrogeologic unit (HGU). Rocks in a model area are first classified as one of ten HGUs based on the rock's ability to transmit groundwater (i.e., nature of their porosity and permeability), which at the NTS is mainly a function of the rock's primary lithology, type and degree of postdepositional alteration, and propensity to fracture.

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Section: Geophysical Investigationsmentioning

confidence: 99%

A Hydrostratigraphic System for Modeling Groundwater Flow and Radionuclide Migration at the Corrective Action Unit Scale, Nevada Test Site and Surrounding Areas, Clark, Lincoln, and Nye Counties, Nevada

Prothro¹,

Drellack²,

Mercadante³

2009

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Characteristics of Fault Zones in Volcanic Rocks Near Yucca Flat, Nevada Test Site, Nevada

Sweetkind¹,

Drake²

2007

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During 2005 and 2006, the USGS conducted geological studies of fault zones at surface outcrops at the Nevada Test Site. The objectives of these studies were to characterize fault geometry, identify the presence of fault splays, and understand the width and internal architecture of fault zones. Geologic investigations were conducted at surface exposures in upland areas adjacent to Yucca Flat, a basin in the northeastern part of the Nevada Test Site; these data serve as control points for the interpretation of the subsurface data collected at Yucca Flat by other USGS scientists. Fault zones in volcanic rocks near Yucca Flat differ in character and width as a result of differences in the degree of welding and alteration of the protolith, and amount of fault offset. Fault-related damage zones tend to scale with fault offset; damage zones associated with large-offset faults (>100 m) are many tens of meters wide, whereas damage zones associated with smaller-offset faults are generally a only a meter or two wide. Zeoliticallyaltered tuff develops moderate-sized damage zones whereas vitric nonwelded, bedded and airfall tuff have very minor damage zones, often consisting of the fault zone itself as a deformation band, with minor fault effect to the surrounding rock mass. These differences in fault geometry and fault zone architecture in surface analog sites can serve as a guide toward interpretation of high-resolution subsurface geophysical results from Yucca Flat.

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