DIMCALC; a BASIC program for computing absolutes and baselines from DIM - magnetometer observations
Explore the source record for details and available documents.
Open-File Report↗
Geology topics
L. W. Pankratz
Publications and source records attributed to L. W. Pankratz.
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↗
Reconnaissance Seismic Refraction Studies at Calico Hills, Wahmonie, and Yucca Mountain, Southwest Nevada Test Site, Nye County, Nevada
Reconnaissance refraction surveys consisting off a total of 5 spreads were conducted in the Calico Hills, Wahmonie and Yucca Mountain areas, southwestern Nevada Test Site (NTS). Data from Calico Hills and Wahmonie are generally high in quality; data from Yucca Mountain are for the most part low in quality. At Calico Hills and Wahmonie, special attention was focused on the possible occurrence of a major intrusive body at depth. At Calico Hills this occurrence is supported by an inferred dome-shaped velocity interface. possibly associated with the roof of an altered phase of argillite. However, if an intrusive body is present, its top must be buried deeper than 3 km or it must be so pervasively altered that its velocity is similar to that of the calcareous argillite encountered at the bottom of drill hole DE 25a-3. At Wahmonie, the seismic data suggest the occurrence of a massive lenticular unit within 60 m of the ground surface, probably consisting of argillite but possibly consisting of intensively altered intrusive rock. At Yucca Mountain, preliminary interpretations of the most reliable data suggest the occurrence of a major, steeply inclined velocity interface 500 m from the southwest end of the Yucca C spread. This interface may represent a major fault or erosional feature separating the Topopah Spring and Tiva Canyon Members with Paintbrush Tuff at depth. This interface is 800 m east of a previously mapped fault. On the basis of poor-quality data obtained at Yucca Mountain, the subsurface velocity distribution appears to be complex. For example, one spread near drill hole UE25 a-I suggests not only a much thicker section of Tiva but also that this material is down thrown in the valley. This may suggest faulting with throws exceeding 100 meters or an equivalent erosional feature.
Open-File Report↗