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D.B. Hoover

Publications and source records attributed to D.B. Hoover.

31 records · Page 2Linked to original sources
USGS1982

Geophysical studies of the Syncline Ridge area, Nevada Test Site, Nye County, Nevada

A wide variety of geophysical methods were employed to study a proposed nuclear waste site at Syncline Ridge on the Nevada Test Site, Nev. The proposed site was believed to be a relatively undisturbed synclinal structure containing a thick argillite unit of Misslsslppian age, the Eleana Formation unit J, which would be the emplacement medium. Data acquisition for the geophysical studies was constrained because of rugged topography in a block of Tipplpah Limestone overlying the central part of the proposed site. This study employed gravity, magnetic, seismic refraction and reflection, and four distinct electrical methods to try and define the structural integrity and shape of the proposed repository medium. Detailed and regional gravity work revealed complex structure at the site. Magnetics helped only in identifying small areas of Tertiary volcanic rocks because of low magnetization of the rocks. Seismic refraction assisted in identifying near surface faulting and bedrock structure. Difficulty was experienced in obtaining good quality reflection data. This implied significant structural complexity but also revealed the principal features that were supported by other data. Electrical methods were used for fault identification and for mapping of a thick argillaceous unit of the Eleana Formation in which nuclear waste was to be emplaced. The geophysical studies indicate that major faults along the axis of Syncline Ridge and on both margins have large vertical offsets displacing units so as not only to make mining difficult, but also providing potential paths for waste migration to underlying carbonate aquifers. The Eleana Formation appeared heterogeneous, which was inferred to be due to structural complexity. Only a small region in the northwest part of the study area was found to contain a thick and relatively undisturbed volume of host rock.

Open-File Report↗
USGS1982

Electrical studies at the proposed Wahmonie and Calico Hills nuclear waste sites, Nevada Test Site, Nye County, Nevada

Two sites in the southwest quadrant of the Nevada Test Site (NTS) were investigated as potential repositories for high-level nuclear waste. These are designated the Wahmonie and Calico Hills sites. The emplacement medium at both sites was to be an inferred intrusive body at shallow depth; the inference of the presence of the body was based on aeromagnetic and regional gravity data. This report summarizes results of Schlumberger VES, induced polarization dipole-dipole traverses and magnetotelluric soundings made in the vicinity of the sites in order to characterize the geoelectric section. At the Wahmonie site VES work identified a low resistivity unit at depth surrounding the inferred intrusive body. The low resistivity unit is believed to be either the argillite (Mississippian Eleana Formation) or a thick unit of altered volcanic rock (Tertiary). Good electrical contrast is provided between the low resistivity unit and a large volume of intermediate resistivity rock correlative with the aeromagnetic and gravity data. The intermediate resistivity unit (100-200 ohm-m) is believed to be the intrusive body. The resistivity values are very low for a fresh, tight intrusive and suggest significant fracturing, alteration and possible mineralization have occurred within the upper kilometer of rock. Induced polarization data supports the VES work, identifies a major fault on the northwest side of the inferred intrusive and significant potential for disseminated mineralization within the body. The mineralization potential is particularly significant because as late as 1928, a strike of high grade silver-gold ore was made at the site. The shallow electrical data at Calico Hills revealed no large volume high resistivity body that could be associated with a tight intrusive mass in the upper kilometer of section. A drill hole UE 25A-3 sunk to 762 m (2500 ft) at the site revealed only units of the Eleana argillite thermally metamorphosed below 396 m (1300 ft) and in part highly magnetic. Subsequent work has shown that much if not all of the magnetic and gravity anomalies can be attributed to the Eleana Formation. The alteration and doming, however, still argue for an intrusive but at greater depth than originally thought. The electrical, VES, and IP data show a complex picture due to variations in structure and alteration within the Eleana and surrounding volcanic units. These data do not suggest the presence of an intrusive in the upper kilometer of section. The magnetotelluric data however gives clear evidence for a thick, resistive body in the earth's crust below the site. While the interpreted depth is very poorly constrained due to noise and structural problems, the top of the resistive body is on the order of 2.5 km deep. The IP data also identifies area of increased polarizability at Calico Hills, which may also have future economic mineralization.

Open-File Report↗
USGS1976

Audio-magnetotelluric methods in reconnaissance geothermal exploration

An audio-magnetotelluric (AMT) system has been developed by the U.S. Geological Survey for low-cost reconnaissance exploration of geothermal regions. This is an electromagnetic sounding technique in which the scalar or Cagniard resistivity is computed at 12 frequencies logarithmically spaced from 7.5 to 18 600 Hz. Our system uses natural source fields except at the two upper frequencies of 10 200 and 18 600 Hz where artificial VLF sources are available. As a reconnaissance technique we use AMT surveys in conjunction with regional gravity, magnetic, and telluric surveys. The exploration depth is a function of the resistivities of the lithologic section, but typically ranges from the surface to 0.2 km in low-resistivity areas and to greater than 2 km in high-resistivity regions. Results of the initial reconnaissance AMT surveys provide a rational basis for deciding on the extent of costlier follow-up surveys. As part of the U.S. Geological Survey geothermal program, surveys were conducted in Long Valley and Surprise Valley, California; the Vale, Ore-Weiser, Idaho region; and Bruneau-Grand View, Raft River, and Island Park regions of Idaho. AMT surveys in five additional known geothermal resource areas (KGRA's) have been scheduled for completion by May 1975. In the Raft River and Bruneau-Grand View regions and Long Valley, follow-up electrical surveys substantiated the effectiveness of the AMT technique for reconnaissance surveying.

Conference Paper↗
USGS1968

Seismic survey in the region of recent earthquake activity near Denver, Colorado

A seismic -reflection survey was carried out near Denver , Colorado , for the U. S. Geological Survey , to determine if structures exist in the 12,000-ft sedimentary section or in the Precambrian basement that might explain the recent earthquake activity . No major faults were revealed in the sedimentary section. Reflections from a steeply dipping horizon believed to be in the basement complex may be indicative of faulting; however, the magnitude cannot be ascertained, as reflection events cannot be correlated at these depths. The results of the survey suggest the possibility of monitoring and studying subsurface structural conditions and related parameters in regions of seismic activity and/or suspected zones of tectonic instability.

Colorado↗