Major results of geophysical investigations at Yucca Mountain and vicinity, southern Nevada

Abstract

(irnteragency Agreement DE-AIO8-92WlO8 74)This report is preliminary and has not been reviewed for conformity with U.S. The use of trade, product, industry, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. .. 11Copies of this report can be purchased from: km) which includes hydrologic, geologic, and environmental study areas. In the consideration of Yucca Mountain as a possible site for storing high-level nuclear waste, a number of geologic concerns have been suggested for study by the National Academy of Sciences which include (1) natural geologic and geochemical barriers, (2) possible hture fluctuations in the water table that might flood a mined underground repository, (3) tectonic stability, and (4) considerations of shaking such as might be caused by nearby earthquakes or possible volcanic eruptions. U. S. Geological SurveyThis volume represents the third part of an overall plan of geophysical investigation of Yucca Mountain, preceded by the Site Characterization Plan (SCP; dated 1988) and the report referred to as the "Geophysical White Paper, Phase I," entitled Status ofData, Major Remlts, and Plum for Geophysical Activities, Yucca Mountain Project (Oliver and others, 1990). The SCP necessarily contained uncertainty about applicability and accuracy of methods then untried in the Yucca Mountain volcano-tectonic setting, and the White Paper, Phase I, focused on summarization of survey coverage, data quality, and applicability of results. For the most part, it did not present data or interpretation. The important distinction of the current volume ("Geophysical White Paper, Phase 11") lies in presentation of data, results, and interpretations of selected geophysical methods used in characterization activities at Yucca Mountain, largely through 1990. Constraints of funding, scheduling, and applicability or availability of methods resulted in unavoidable variability of time fiame of individual investigations. Separate chapters combined here were completed at various times over several years.Yucca Mountain consists of a series of north-trending, eastward-tilted structural blocks bounded by steeply westward-dipping Cenozoic faults. These blocks consist of temgenous volcanic and Some of the most important geologic questions that need to be answered are (1) the depth to, and nature of, the contact between the Cenozoic and Paleozoic rocks, (2) the origin and possible activity of the Quaternary faults, (3) the origin and stability of a rise of about 300 m in the potentiometric surface to the north of an approximate boundary of a potential repository, and (4) the possibility of fbture nearby volcanic activity. As the surface of Yucca Mountain is largely covered with Miocene volcanic flows assigned to the Tiva Canyon Tuff of the Paintbrush Group, geophysical methods and drilling are required to determine the subsurface structure and to answer these questions.Gravity investigations began about 1979 at Yucca Mo...

Geophysical framework of the southwestern Nevada volcanic field and hydrogeologic implications

“…4). This boundary has also been recognized by previous workers as the southern limit of a broad, regional, east-trending magnetic high (e.g., Bath and Jahren, 1984;Oliver, Ponce, and Blank, 1995). However, the magnetic potential map indicates the southern limit of high bulk magnetization is actually about 10 km farther north ( fig.…”

“…The presence of the Eleana confining unit north of Yucca Mountain could also explain the hydraulic gradient (Fridrich, Dudley, and Stuckless, 1994). However, the magnetic source of the regional high is estimated at 1.5-to 3.0-km depth (Ponce and others, 1995;Oliver, Ponce, and Blank, 1995). At the depths indicated, a large volume of magnetic material is required to explain the magnetic high.…”

“…At the depths indicated, a large volume of magnetic material is required to explain the magnetic high. Therefore, a granitic intrusion or batholith is more likely to be the primary source, perhaps with some contribution from magnetized argillite (Kane and Bracken, 1983;Carr and others, 1986;Oliver, Ponce, and Blank, 1995).…”

Site characterization progress report: Yucca Mountain, Nevada. Number 15, April 1--September 30, 1996

“…The aeromagnetic and ground gravity regional potential field data sets have been synthesized, and final interpretations and subsurface structural models are being generated for further analysis and to support the tectonics, volcanism, and hydrologic investigations. Follow-up documentation for many of the geophysical activities and proposed testing A-35 PROGRESS REPORT #15 programs were presented in the 1990 and 1995 Geophysics White Papers (DOE, 1990;Oliver et al, 1995. Most of the standard and prototype testing programs outlined in DOE (1990) were conducted during the past five years.…”

Geologic Framework Model Analysis Model Report

“…A summary of these data is presented in Oliver et al (1995). For input, a model requires spatial location (x-y coordinates and elevation) and specific geometry and identity of faults and stratigraphic units, which is not generally provided by the data obtainable from these geophysical methods.…”