Geology of the Source Physics Experiment Site, Climax Stock, Nevada National Security Site

Abstract

A test bed for a series of chemical explosives tests known as Source Physics Experiments (SPE) was constructed in granitic rock of the Climax stock, in northern Yucca Flat at the Nevada National Security Site in 2010-2011. These tests are sponsored by the U.S. Department of Energy, National Nuclear Security Administration's National Center for Nuclear Security. The test series is designed to study the generation and propagation of seismic waves, and will provide data that will improve the predictive capability of calculational models for detecting and characterizing underground explosions. Abundant geologic data are available for the area, primarily as a result of studies performed in conjunction with the three underground nuclear tests conducted in the Climax granite in the 1960s and a few later studies of various types.The SPE test bed was constructed at an elevation of approximately 1,524 meters (m), and consists of a 91.4-centimeter (cm) diameter source hole at its center, surrounded by two rings of three 20.3-cm diameter instrument holes. The inner ring of holes is positioned 10 m away from the source hole, and the outer ring of holes is positioned 20 m from the source hole. An initial 160-m deep core hole was drilled at the location of the source hole that provided information on the geology of the site and rock samples for later laboratory testing. A suite of geophysical logs was run in the core hole and all six instruments holes to obtain matrix and fracture properties.Detailed information on the character and density of fractures encountered was obtained from the borehole image logs run in the holes. A total of 2,488 fractures were identified in the seven boreholes, and these were ranked into six categories (0 through 5) on the basis of their degree of openness and continuity. The analysis presented here considered only the higher-ranked fractures (ranks 2 through 5), of which there were 1,215 (approximately 49 percent of all fractures identified from borehole image logs). The fractures were grouped into sets based on their orientation. The most ubiquitous fracture set (50 percent of all higher-ranked fractures) is a group of low-angle fractures (dips 0 to 30 degrees). Fractures with dips of 60 to 90 degrees account for 38 percent of high-ranked fractures, and the remaining 12 percent are fractures with moderate dips (30 to 60 degrees). The higher-angle fractures are further subdivided into three sets based on their dip direction: fractures of Set 1 dip to the north-northeast, fractures of Set 2 dip to the south-southwest, and Set 3 consists of high-angle fractures that dip to the southeast and strike northeast. The low-angle fractures (Set 4) dip eastward. Fracture frequency does not appear to change substantially with depth. True fracture spacing averages 0.9 to 1.2 m for high-angle Sets 1, 2, and 3, and 0.6 m for Set 4. Two significant faults were observed in the core, centered at the depths of 25.3 and 32.3 m. The upper of these two faults dips 80 degrees to the north-northeast and, thus, is...

Chemical Explosion Experiments to Improve Nuclear Test Monitoring

“…Site characterization includes detailed geologic studies of the test bed [Townsend et al, 2012] and material property measurements of the granite from core samples and of material within fault zones using standard and custom laboratory tests. Gravity surveys showed changes in apparent near-surface density after the SPE-2 explosion.…”

An Explosion Model Comparison with Insights from the Source Physics Experiments

“…In contrast the MM amplitudes in Figure 10 are much larger than observed. We note that the near--source velocities in Models 2 and 3 are below the range presented in Townsend et al (2012), and the MM--predicted waveforms from these models are even larger those from Model 1. These results indicate the low frequency MM mismatch with the observations holds even given the uncertainties in the velocity models.…”

“…Townsend et al (2012) report a range of near--source parameters for different measurement methods and agencies. Given this uncertainty, we calculate the transfer function SPE2/SPE1 ratio for the whole range of values of compressional velocity, shear velocity, density, and porosity of 4700 to 5928 m/s, 2900 to 3700 m/s, 2635 to 2670 m/kg 3 , and 0.7 to 3.2%, respectively.…”

“…We create synthetics for three simple one--dimensional velocity models (Table 3). Velocity model 1 is a simple weathered layer over granite derived from data presented in Townsend et al (2012). Velocity model 2 is from the study of Rowe et al (2012) and velocity model 3 is from the Rg dispersion work of Patton (2012).…”

A thermomechanical anisotropic continuum model for geological materials with multiple joint sets

“…One of the goals of this experimental program was to understand the mechanism causing generation of this shear wave. Rock samples excavated at the site from different depths were tested in the laboratory, and the observed variations in mechanical properties were not significant enough to explain the generation of shear waves . In addition, joint orientations and their mechanical properties were characterized at various locations in the site.…”