Weapons test seismic investigations at Yucca Mountain Page: 3 of 17
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' alluvium/tuff interface) instrumentation, whereas W26 has only surface
Not all UNEs conducted at NTS are monitored by WTSI. The selection of
which UNEs to monitor is based on the explosive yields. UNE yields between 80
and 150 kt are of greatest interest to the YMP. These UNEs are usually
conducted in the Pahute Mesa (Areas 19 and 20) and Yucca Flat testing areas of
the NTS. The distance between these testing areas and Yucca Mountain varies
from about 35 km to 55 km. The lower yield limit was selected because ground
motions generated by yields below 80 kt, at these distances, are of a very low
amplitude (approximately 2 orders of magnitude below those expected for the
design basis). While data from these lower yield UNEs would contribute to the
study of seismic wave transmission at the site, they are of little value in
the development of the amplitude or frequency prediction of ground motions for
the design-basis event. The upper yield limit is mandated by the Threshold
Test Ban Treaty of March 1976.
Figure 1 shows the location of UNEs monitored at Yucca Mountain as of the
end of FY90 compared to the location of t'e design-basis UNE. Based on
available NTS geologic data, the source geology at the Buckboard Area is
thought to be similar to that at Pahute Mesa. But from Figure 1 it is
apparent that the travel path azimuth of the design-basis UNE is similar to
the events in Yucca Flat and therefore, path effects observed in the Yucca
Flat data might be indicative of what could be expected from the design-basis
Because the UNE-generated ground-motion data recorded at Yucca Mountain
are from explosions with limited variability in yield and distance, and
because the yield and location of the design-basis UNE are not within the
monitored ranges, it was important to assemble a data base which included
ground-motion data from other UNEs that bracketed the yield and distance
parameters associated with the design-basis UNE. Ground motion generated by
UNEs has been of interest since the beginning of underground weapons testing.
Measurements of ground motion have been made on explosions with yields up to
1400 kt, at both close-in locations (distances within a few burial depths of
the explosion) and at seismic distances (tens of burial depths from the
explosion). Many of these data have been used to develop prediction models
for the amplitude of ground motion and to study the transmission
characteristics of the NTS area. These studies were conducted before the YMP
began and are not directly applicable to the Project. However, the data from
some of these older UNEs exist on tape and have been analyzed in the context
of the YMP.
WTSI GROUND-MOTION DATA BASE
The UNE ground-motion data base assembled by the WTSI project for the YMP
consists of data from a total of 84 UNEs (57 from Pahute Mesa and 27 from
Yucca Flat). Of this number, 46 have been recorded at Yucca Mountain seismic
stations. The remainder of the UNEs that make up the data base are earlier
events with yields ranging up to 1400 kt and recording stations located at
various pc,:ts on the NTS at distances of 1 km and greater. The data base
brackets the yield and the distance parameters of the design-basis UNE.
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Phillips, J.S.; Shephard, L.E. & Walck, M.C. Weapons test seismic investigations at Yucca Mountain, article, January 1, 1991; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc620294/m1/3/: accessed November 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.