Yucca Flat Research Articles

Airblast observations and near-field modeling of the large surface explosion coupling experiment

Seismoacoustic wave generation for two consecutive surface chemical explosions of the same yield (approximately 1 ton TNT-equivalent) was studied during the Large Surface Explosion Coupling Experiment (LSECE) conducted at Yucca Flat on the Nevada National Security Site (NNSS) site in alluvium geology. We have performed numerical simulations for both chemical explosions to investigate how the non-central source initiation, site topography and soil mechanical properties affect the evolution of the explosion (fireball and cloud), its crater, and variations in the generated blast waves. The results can be used to improve the understanding of surface explosions and their effects and how those effects can be used to infer source information such as explosive yield and emplacement. We find that the non-central detonation of the explosive cube results in non-axisymmetric blast overpressures which persist through the strong and weak shock regimes, in this case out to 200 m and more. The pattern of the secondary shock (i.e., shock created due to slowing explosive products within the expanding fireball) is also affected and its arrival relative to the main shock and may be indicative of explosive type due to its dependence on the explosive products ratio of heats. Small reflections are visible within the overpressure signal that are most probably due to small artifacts in blast path. Importantly, the fireball growth, cavity generation, and cloud formation also depart from spherical and ideal approximations due to ground interactions and material dependence, which shows the importance of realistic geomaterial models for accurate prediction. The asymmetry in peak overpressure is diminished for the second chemical explosion, which was placed in the crater of the first. Numerical modeling shows that the explosive jetting created by the non-central detonation is reduced upon interaction with the crater walls and this has the effect of making the blast generation more axisymmetric.

Deep learning to estimate the basement depth by gravity data using a feedforward neural network

We have developed a deep-learning method based on the neural network of the feedforward type to estimate the depth to the basement from potential fields. The data used to train and test the network are related to the Bishop synthetic model. A trial-and-error approach was used to find the hyperparameters that have the best compromise between performance and computation time. The training was organized by associating the depth values of the basement to the data through a moving window, running along profiles in the north–south and east–west directions. In this way, we generated a set of approximately 296,980 examples. We verified the robustness of the trained net by carrying out a test related to another synthetic model, extracted from the Himalaya digital elevation model. The inherent ambiguity of the problem led us to test two hypotheses for the estimation of the basement depth, the first related to a priori information on the density contrast and the shallowest depth and the second assuming the knowledge of the depth at least at two points, but not that of the density contrast. In these cases, our data-driven approach yielded interesting results leading to estimate the maximum depth in the first case and the density contrast in the second one. We finally applied the method to the isostatic anomaly of the Yucca Flat sedimentary basin, Nevada. The results are consistent with previous interpretations of the area, which were based on gravity inversion methods.

Seismoacoustic Explosion Yield and Depth Estimation: Insights from the Large Surface Explosion Coupling Experiment

ABSTRACT The Large Surface Explosion Coupling Experiment (LSECE) is a chemical explosion experiment conducted in Yucca Flat at the Nevada National Security Site in 2020. The experiment included two surface detonations of ∼1000 kg trinitrotoluene equivalent. The main goal of this experiment was to provide the ground-truth data for seismoacoustic wave excitation by large chemical explosions near the ground surface. The seismic and acoustic energy partitioning between the surface is strongly governed by the depth or height of explosions, and either seismic or acoustic-only analysis may have inherent ambiguity in determining explosion yield and depth simultaneously. Previous studies suggested that joint seismoacoustic analysis can resolve the trade-off and reduce the uncertainty of yield and depth estimation dramatically. We demonstrate the capability of seismoacoustic analysis to improve the accuracy of explosion yield and depth estimation with the LSECE data. Local acoustic wave propagation in the atmosphere can be substantially affected by constantly varying weather conditions. Consisting of two detonations before dawn and in the afternoon, LSECE provides unique data to evaluate the model accuracy of acoustic wave propagation and seismoacoustic energy partitioning depending on local atmospheric conditions. We quantitatively evaluate the accuracy of yield and depth estimation depending on atmospheric variability and the improvement achieved by the joint seismoacoustic approach.

TRAVEL TIME CURVES FOR YUCCA TEST SITE (NEVADA TEST SITE) – SEISMIC ARRAYS «OZHEREL’E» (GEOPHYSICAL OBSERVATORY «BOROVOYE»)

This paper presents the travel times of P waves for 8 Yucca Flat (Nevada Test Site NTS) explosions from 1979 to 1984, with magnitudes mb = 4.9–5.9. Travel times were obtained by revising seismograms from the archives Sadovsky Institute of Geosphere Dynamics for the subsystem “Ozherel’e” (Necklace) of peripheral points Zerenda, Vostochniy, Chkalovo of the large-base seismic array system (SAS) of the geophysical observatory Borovoye. This system has been operating since 1979 on the territory of Kazakhstan. By the example of registration of underground nuclear explosions at the Yucca site of the Nevada Test Site (NTS), local travel time curves and linear trends in the P wave travel time in the range of epicentral distances 89.3110°–90.3701° are investigated. We estimate of the velocities of effective P waves for the Yucca-“Ozherel’e” and peripheral points.

Subsurface microbial communities as a tool for characterizing regional-scale groundwater flow

Subsurface microbial community distribution patterns are influenced by biogeochemical and groundwater fluxes and may inform hydraulic connections along groundwater-flow paths. This study examined the regional-scale microbial community of the Death Valley Regional Flow System and evaluated whether subsurface communities can be used to identify groundwater-flow paths between recharge and discharge areas. Samples were collected from 36 sites in three groundwater basins: Pahute Mesa–Oasis Valley (PMOV), Ash Meadows (AM), and Alkali Flat–Furnace Creek Ranch (AFFCR). Microbial diversity within and between communities varied by location, and communities were separated into two overall groups that affiliated with the AM and PMOV/AFFCR basins. Network analysis revealed patterns between clusters of common microbes that represented groundwaters with similar geochemical conditions and largely corroborated hydraulic connections between recharge and discharge areas. Null model analyses identified deterministic and stochastic ecological processes contributing to microbial community assemblages. Most communities were more different than expected and governed by dispersal limitation, geochemical differences, or undominating processes. However, certain communities from sites located within or near the Nevada National Security Site were more similar than expected and dominated by homogeneous dispersal or selection. Overall, the (dis)similarities between the microbial communities of DVRFS recharge and discharge areas supported previously documented hydraulic connections between: (1) Spring Mountains and Ash Meadows; (2) Frenchman and Yucca Flat and Amargosa Desert; and (3) Amargosa Desert and Death Valley. However, only a portion of the flow path between Pahute Mesa and Oasis Valley could be supported by microbial community analyses, likely due to well-associated artifacts in samples from the two Oasis Valley sites. This study demonstrates the utility of combining microbial data with hydrologic, geologic, and water-chemistry information to comprehensively characterize groundwater systems, highlighting both strengths and limitations of this approach.

Assessing the Accuracy of a Borehole-Controlled P-Wave Velocity Model of Yucca Flat, Nevada Using Large-N Seismic Data

ABSTRACT With geologic data from over 950 boreholes, Yucca Flat basin, residing on the Nevada National Security Site, has excellent borehole control on stratigraphy. These data were used to create a Geologic Framework Model (GFM) of the basin. Of these boreholes, 188 have corresponding downhole seismic survey data, which were used to determine average P-wave velocities of the geologic units and create a GFM seismostratigraphic model (GFM-SS). With the acquisition of six new active-source large-N datasets in Yucca Flat, we can now quantitatively assess the accuracy of the GFM-SS previously controlled only by borehole data. For each of the six datasets, we subset the GFM to the region of interest and create a forward model of P-wave travel times for the GFM-SS given the large-N source-receiver geometries. We first made trial-and-error adjustments to the unit velocities (while keeping the layer geometry intact) to improve the travel-time residuals. We then implemented a simulated annealing approach to find the optimal velocity model for each dataset. Our results indicate that the borehole-controlled model overestimates alluvium velocities across Yucca Flat. This result persists even when we make smaller GFM-SS models that are local to individual large-N experiments. We hypothesize that this result is a combination of shorter ray paths and the resulting lack of interaction with large-scale features (such as faults), as well as less attenuation of high frequencies in the borehole data. Both the current GFM-SS and the updated model based on median velocities that we present here overgeneralize local unit velocities, which can be quite heterogeneous in Yucca Flat.

Exhibition Review: Devour the Land: War and American Landscape Photography since 1970

Exhibition Review: <i>Devour the Land: War and American Landscape Photography since 1970</i>

Modified Parker's Method for Gravitational Forward and Inverse Modeling Using General Polyhedral Models

AbstractWe propose a new modified Parker's method for efficient gravitational forward modeling and inversion using general polyhedral models. We have made several important modifications to the classical method, including: (a) The new method is now applicable to a general polyhedron represented by triangulated surface or tetrahedral mesh, and with arbitrarily variable 3D density distribution. (b) An optimal Fourier‐domain sampling strategy is used to improve the numerical accuracy of the new algorithm significantly. (c) A simple and effective automatic layering technique is introduced to accelerate the convergence rate of Parker's method. The method is demonstrated using both synthetic and real polyhedral models, including a sphere model approximated by a polyhedron, two asteroids, a digital elevation model in the Himalaya region, and the Yucca Flat basin model in Nevada. The numerical results show that, compared with analytical solutions of polyhedral models in the space domain, the modified Parker's method can improve the computational efficiency by several orders of magnitude while obtaining almost the same simulation results. The difference is well below existing instrumentation error level. By embedding the new forward algorithm into an iterative process, it can be used for fast inversion of density interfaces. Our new method is suitable for the efficient modeling and inversion of gravitational potential, gravitational vector, and gravitational gradient tensor caused by polyhedral models with a large number of faces, representing geological abnormal bodies, asteroids, and single or multilayer density interface models with triangulated surfaces.

Mosquito Distribution and West Nile Virus Surveillance Results on the Nevada National Security Site in South-Central Nevada

A 10-year study (2004–2013) was conducted to determine mosquito distribution and the prevalence of West Nile virus (WNV) on the Nevada National Security Site (NNSS) in south-central Nevada. Mosquito traps baited with dry ice were set overnight at sites where standing water provided potential breeding sites for mosquitoes. Captured mosquitoes were identified to species and tested for WNV. A total of 556 mosquitoes representing 6 species were captured and identified at 20 sites around the NNSS during 124 surveys. A vast majority (89%) of mosquitoes were Culex tarsalis. Two samples, both Culiseta inornata, tested positive for WNV in 2005 and 2006, both from Well 3 Pond, Yucca Flat, Nye County. Additionally, 24 birds representing 5 species were opportunistically collected and tested for WNV with no positive results. Results from this study reveal patterns of mosquito distribution across the NNSS and suggest that NNSS workers are at low risk of being exposed to WNV.

Preliminary Analysis of Source Physics Experiment Explosion‐Triggered Microseismicity Using the Back‐Projection Method

AbstractA series of four chemical explosions were detonated in a deep borehole within the Yucca Flat Dry Alluvium Geology (DAG) at the Nevada National Security Site between 2018 and 2019. The two larger chemical explosions of 50 tons (DAG‐2) and 10 tons (DAG‐4) TNT equivalent yield triggered energetic aftershock sequences numbering 1392 and 347 microearthquakes, respectively, within the first 10 days. No significant aftershock activity was observed for the two smaller 1‐ton explosions (DAG‐1 and DAG‐3). We used a back‐projection method based on travel‐time migration and stacking of signal‐to‐noise ratio traces to detect, associate and locate aftershocks from a subset of 22‐geophones within a larger 2 2 km seismic array surrounding the borehole. The aftershocks located within 300 m of the borehole and the depths were above the working points of 300 and 50 m depths of DAG‐2 and DAG‐4, respectively, ruling out triggering slip on geologic faults or disturbances beneath neighboring collapse craters. DAG‐2 and DAG‐4 aftershocks decayed at similar rates, with power‐law exponents of p = 1.48 and p = 1.49, respectively. These decay rates are comparable to aftershocks sequences triggered by earthquakes and historical nuclear explosions at Yucca Flat. A smooth power‐law aftershock decay within the first 10 days suggests a triggering mechanism from explosion generated stress relaxation due to the diffusion of high gas pressures in the cavity and radial fractures. A more random and episodic aftershock rate would be expected due to cavity collapse or falling rubble in chimney formation.

Imaging the Shallow Structure of the Yucca Flat at the Source Physics Experiment Phase II Site with Horizontal-to-Vertical Spectral Ratio Inversion and a Large-N Seismic Array

AbstractThe Source Physics Experiment (SPE) is a series of chemical explosions at the Nevada National Security Site (NNSS) with the goal of understanding seismic-wave generation and propagation of underground explosions. To understand explosion source physics, accurate geophysical models of the SPE site are needed. Here, we utilize a large-N seismic array deployed at the SPE phase II site to generate a shallow subsurface model of shear-wave velocity. The deployment consists of 500 geophones and covers an area of, approximately, 2.5×2 km. The array is located in the Yucca Flat in the northeast corner of the NNSS, Nye County, Nevada. Using ambient-noise recordings throughout the large-N seismic array, we calculate horizontal-to-vertical spectral ratios (HVSRs) across the array. We obtain 2D seismic images of shear-wave velocities across the SPE phase II site for the shallow structure of the basin. The results clearly image two significant seismic impedance interfaces at ∼150–500 and ∼350–600 m depth. The shallower interface relates to the contrast between Quaternary alluvium and Tertiary volcanic rocks. The deeper interface relates to the contrast between Tertiary volcanic rocks and the Paleozoic bedrock. The 2D subsurface models support and extend previous understanding of the structure of the SPE phase II site. This study shows that the HVSR method in conjunction with a large-N seismic array is a quick and effective method for investigating shallow structures.

The priority of microgravity focusing inversion in 3D modeling of subsurface voids

Geophysical methods can be used to detect voids, cavities, and tunnels. Inversion of microgravity data provides the distribution of the subsurface density. It can be effective to reconstruct concealed cavities and other underground openings, as they are often at different depths that have a low density. We have smooth and focusing inversion methods that apply the minimum norm and minimum support stabilizers. In this study, we used smooth and focusing inversion methods by reweighted regularized conjugate gradient (RRCG) method for inverting microgravity data. Here, these methods are utilized to inversion of microgravity data from two synthetic models and a microgravity data set over a tunnel located in Yucca Flat, Nevada. The results demonstrated smooth inversion cannot detect sharp boundaries and overestimates the bottom depths of the underground openings, but the focusing inversion method recovers models with sharp boundaries and does not have the problems of the previous method. The results indicate the priority of the focusing inversion method for the detection of voids by microgravity data.

Using Dense Array Waveform Correlations to Build a Velocity Model with Stochastic Variability

ABSTRACTIn an ongoing effort to improve 3D seismic-wave propagation modeling for frequencies up to 10 Hz, we used cross correlations between vertical-component waveforms from an underground chemical explosion to estimate the statistical properties of small-scale velocity heterogeneities. The waveforms were recorded by a dense 2D seismic array deployed during the Source Physics Experiments for event number 5 (SPE-5) in a series of six underground chemical explosions, conducted at the Nevada National Security Site. The array consisted of 996 geophones with a 50–100 m grid spacing, deployed at the SPE site at the north end of the Yucca Flat basin. The SPE were conducted to investigate the generation and propagation of seismic and acoustic waves from underground explosions.Comparisons of decay rates of waveform cross correlations as function of interstation distance, computed for observed and synthetic seismograms from the SPE-5 chemical explosion, were used to constrain statistical properties of correlated stochastic velocity perturbations representing small-scale heterogeneities added to a geology-based velocity model of the Yucca Flat basin. Using comparisons between recorded and simulated waveform cross correlations, we were able to recover sets of statistical properties of small-scale velocity perturbations in the velocity model that produce the best-fit between the recorded and simulated ground motion. The stochastic velocity fluctuations in the velocity model that produced the smallest misfits have a horizontal correlation distance of between 400 and 800 m, a vertical correlation distance between 100 and 200 m, and a standard deviation of 10% from the nominal model velocity in the alluvium basin layers. They also have a horizontal correlation distance of 1000 m, a vertical correlation distance of 250 m, and a standard deviation of 6% in the underlying and consolidated sedimentary layers, up to a depth of 4 km.Comparisons between observed and simulated wavefields were used to assess the proposed small-scale heterogeneity enhancements to the Yucca Flat basin model. We found that adding a depth-resolved stochastic variability to the geology-based velocity model improves the overall performance of ground-motion simulations of an SPE-5 explosion in the modeled frequency range up to 10 Hz. The results may be applicable to other similar basins.

Beyond the Black and White TV: Asian and Latin American Spectacle in Cold War America by Benjamin M. Han

Reviewed by: Beyond the Black and White TV: Asian and Latin American Spectacle in Cold War America by Benjamin M. Han Victor Wu (bio) Beyond the Black and White TV: Asian and Latin American Spectacle in Cold War America, by Benjamin M. Han. New Brunswick, NJ: Rutgers University Press, 2020. 216 pp. $27.95 paper. ISBN 978-1-9788-0383-1. Benjamin M. Han’s debut book, Beyond the Black and White TV, reexamines the oft-overlooked roles of Asian and Latin American ethnic entertainers in American television against the backdrop of the cultural Cold War. Because the Asia-Pacific and Latin America were two critical geopolitical spaces for the expansion of US hegemony, Han argues that the transnational circulation of Asian and Latin American performers on US commercial television functioned as Cold War cultural diplomacy that promoted American internationalism and waged ideological battles against the encroaching threat of communism in those regions. Han draws upon Marxist philosopher Guy Debord’s concept of spectacle as a “false representation of reality through the mass dissemination of images” (7) to postulate that the “ethnic spectacle” mediated by Cold War– era television fabricated a narrative of the United States as being a bastion of racial equality and democracy. Han asserts that this narrative was birthed in direct response to Soviet criticism of its anti-Black racism, which was growing increasingly visible due to the civil rights movement and was damaging the nation’s image on a global scale. Beyond the Black and White TV specifically examines the variety show as a site of transnational cultural interventionism that was informed by a “triangulation among Cold War geopolitics, globalism, and U.S. racial logics” (19). Because the variety show “functioned as both education and entertainment” (4), it was uniquely suited for America’s rebranding efforts. Variety shows often featured white hosts, who served as cultural interlocuters that interviewed ethnic entertainers about their backgrounds and sang American popular songs alongside them. This emphasis on international understanding, along with the surge of Asian and Latin American performers beginning in the early 1950s, allowed the variety show to project a false image of America as an antiracist nation. While variety show broadcasts initially only targeted domestic audiences and American military personnel abroad, Han shows how these broadcasts served as an “early itineration of global television” (19) that in the late 1950s provided [End Page 345] the blueprint for the dissemination of American Cold War narratives through transnational networks. The book is split into four modular chapters detailing four geographically separate yet unexpectedly analogous spaces where television played a significant role in America’s political agenda during the Cold War: Las Vegas, Korea, Cuba, and Hawaii. Han uses a wide range of historical materials such as television archives and oral histories to trace the development of television as well as the careers of ethnic performers such as the Kim Sisters, the De Castro Sisters, Alfred Apaka, and Don Ho. He examines not just the contexts of their careers but also the contents of their performances, interrogating the ways in which they contested and reinforced investment in whiteness. Chapter 1 looks at Las Vegas as a culturally and militarily significant locus during the Cold War. One of the earliest televised broadcasts of Las Vegas was of the atomic bomb testing on Yucca Flat in 1951, which served as Las Vegas’s introduction to the American public imaginary as a city crucial to national security. This was a far cry from Sin City’s previous negative association with crime, and entertainment personalities saw television as an opportunity to clean up the city’s image and promote American internationalism. Han posits that the later influx of Asian and Latin American entertainers in the 1950s to the Las Vegas nightlife and television scene was part of an attempt to portray the city as an integrated, family-friendly destination. And by the late 1970s, entertainment personalities were using television to capitalize on ethnic spectacle in order to “shed previous depictions of Las Vegas” (37). Consequently, the American government used these televisual images to show off Las Vegas as a racially integrated city that “was representative of American ideals and values” (33). Han explores how...

Improved 3D Cauchy-type Integral for Faster and More Accurate Forward Modeling of Gravity Data Caused by Basement Relief

In this study, a new approach to improve the 3D Cauchy-type integral is presented for faster and more accurate forward modeling of gravity data produced by a sediment-basement interface. The conventional method for calculating the gravity effect of a sedimentary basin is to discretize that into right-rectangular prisms. Its associated volumetric integral over the prisms has computational complexity which makes volumetric integral time-demanding for 3D modeling. A 3D Cauchy-type integral only discretizes the density contrast surface. In fact, it is a surface integral without transcendental functions, which enables fast computation of potential fields. The purpose of the technique is to increase the accuracy of the customary Cauchy-type integral in order to calculate the gravity field over a sedimentary structure which is more likely in real geological structures. To achieve this, the vertical planes located between basement edges and the horizontal reference plane are considered. The accuracy and computational cost is assessed by synthetic gravity data modeling. Three forward functions, namely improved Cauchy-type integral, customary Cauchy-type integral, and volumetric integral, are applied to calculate the gravity field over synthetic sedimentary basins with different geometries. The volumetric integral is set as a benchmark to validate the efficiency of the presented method. Results are analyzed by comparing the dissimilarities of gravity anomalies calculated using the volumetric integral and each of the customary and improved Cauchy-type integrals. The resulting anomaly differences indicate that, compared with the customary Cauchy-type integral, the improved Cauchy-type integral increases the accuracy in calculated gravity anomalies considerably. Furthermore, forward calculations using the improved Cauchy-type integral require approximately the same time as the customary Cauchy-type integral, and are about 50 times faster than the volumetric integral. In addition, the improved Cauchy-type integral gives better results if the edges of the basement are not at an equal level, which is very likely in real geological structures. The new approach is tested on the basement of the Yucca Flat basin to assess the viability of the proposed model in real cases.

Effect of Random 3D Correlated Velocity Perturbations on Numerical Modeling of Ground Motion from the Source Physics Experiment

ABSTRACTExplosions are traditionally discriminated from earthquakes, using the relative amplitude of compressional and shear waves at regional and teleseismic distances known as the P/S discriminant. Pyle and Walter (2019) showed this technique to be less robust at shorter distances, in detecting small-magnitude earthquakes and low-yield explosions. The disparity is largely due to ground motion from small, shallow sources being significantly impacted by near-surface structural complexities. To understand the implications of wave propagation effects in generation of shear motion and P/S ratio during underground chemical explosions, we performed simulations of the Source Physics Experiment (SPE) chemical explosions using 1D and 3D velocity models of the Yucca Flat basin. All simulations used isotropic point sources in the frequency range 0–5 Hz. We isolate the effect of large-scale geological structure and small-scale variability at shallow depth (&amp;lt;5 km), using a regional 3D geologic framework model (GFM) and the GFM-R model derived from the GFM, by adding correlated stochastic velocity perturbations. A parametric study of effects of small-scale velocity variations on wave propagation, computed using a reference 1D velocity model with stochastic perturbations, shows that the correlation length and depth of stochastic perturbations significantly impact wave scattering, near-surface wave conversions, and shear-wave generation. Comparisons of recorded and simulated waveforms for the SPE-5 explosion, using 3D velocity models, demonstrate that the shallow structure of the Yucca Flat basin contributes to generation of observed shear motion. The inclusion of 3D wave scattering, simulated by small-scale velocity perturbations in the 3D model, improves the fit between the simulated and recorded waveforms. In addition, a relatively low intrinsic attenuation, combined with small-scale velocity variations in our models, can confirm the observed wave trapping and its effect on duration of coda waves and the spatial variation of P/S ratio at basin sites.

Joint Body‐ and Surface‐Wave Tomography of Yucca Flat, Nevada, Using a Novel Seismic Source

AbstractIn preparation for the next phase of the Source Physics Experiments, we acquired an active‐source seismic dataset along two transects totaling more than 30 km in length at Yucca Flat, Nevada, on the Nevada National Security Site. Yucca Flat is a sedimentary basin which has hosted more than 650 underground nuclear tests (UGTs). The survey source was a novel 13,000 kg modified industrial pile driver. This weight drop source proved to be broadband and repeatable, richer in low frequencies (1–3 Hz) than traditional vibrator sources and capable of producing peak particle velocities similar to those produced by a 50 kg explosive charge. In this study, we performed a joint inversion of P‐wave refraction travel times and Rayleigh‐wave phase‐velocity dispersion curves for the P‐ and S‐wave velocity structure of Yucca Flat. Phase‐velocity surface‐wave dispersion measurements were obtained via the refraction microtremor method on 1 km arrays, with 80% overlap. Our P‐wave velocity models verify and expand the current understanding of Yucca Flat’s subsurface geometry and bulk properties such as depth to Paleozoic basement and shallow alluvium velocity. Areas of disagreement between this study and the current geologic model of Yucca Flat (derived from borehole studies) generally correlate with areas of widely spaced borehole control points. This provides an opportunity to update the existing model, which is used for modeling groundwater flow and radionuclide transport. Scattering caused by UGT‐related high‐contrast velocity anomalies substantially reduced the number and frequency bandwidth of usable dispersion picks. The S‐wave velocity models presented in this study agree with existing basin‐wide studies of Yucca Flat, but are compromised by diminished surface‐wave coherence as a product of this scattering. As nuclear nonproliferation monitoring moves from teleseismic to regional or even local distances, such high‐frequency (&gt;5 Hz) scattering could prove challenging when attempting to discriminate events in areas of previous testing.

Evaluating Groundwater Interbasin Flow Using Multiple Models and Multiple Types of Data.

The groundwater interbasin flow, Qy , from the north of Yucca Flat into Yucca Flat simulated using the Death Valley Regional Flow System (DVRFS) model greatly exceeds assessments obtained using other approaches. This study aimed to understand the reasons for the overestimation and to examine whether the Qy estimate can be reduced. The two problems were tackled from the angle of model uncertainty by considering six models revised from the DVRFS model with different recharge components and hydrogeological frameworks. The two problems were also tackled from the angle of parametric uncertainty for each model by first conducting Morris sensitivity analysis to identify important parameters and then conducting Monte Carlo simulations for the important parameters. The uncertainty analysis is general and suitable for tackling similar problems; the Morris sensitivity analysis has been utilized to date in only a limited number of regional groundwater modeling. The simulated Qy values were evaluated by using three kinds of calibration data (i.e., hydraulic head observations, discharge estimates, and constant-head boundary flow estimates). The evaluation results indicate that, within the current DVRFS modeling framework, the Qy estimate can only be reduced to about half of the original estimate without severely deteriorating the goodness-of-fit to the calibration data. The evaluation results also indicate that it is necessary to develop a new hydrogeological framework to produce new flow patterns in the DVRFS model. The issues of hydrogeology and boundary flow are being addressed in a new version of the DVRFS model planned for release by the U.S. Geological Survey.

Atomic Screen Test

Atomic Screen Test Jennifer Fay (bio) Atomic Disappointment On April 22, 1952 Americans watched the first televised live broadcast of an atomic explosion. A relay of cables and microwave transmissions from the Yucca Flats Proving Grounds to the Los Angeles KTLA station brought the blast into millions of living rooms using the latest and most innovative telecast technology. Yet, as the countdown commenced, in place of the much-anticipated sublimity of scientific triumph, viewers were instead witness to a kind of televisual failure or electronic gag. Just before the blast, the crew lost microwave power and had to shift the signal to the even more remote back-up camera some forty miles away. The greater challenge, however, was the explosion itself. At the moment of detonation, the camera, overwhelmed by atomic light, transcribed nuclear fission into a tiny white dot in the middle of a black sphere, as if it were the television and not the desert warming up. The image momentarily flickered only to fade into indistinct grey scales when the signature mushroom cloud formed.1 New York Times television critic Jack Gould mused that during the broadcast it seemed as if “electronic gremlins had taken charge.” At its most dramatic, the explosion appeared like “a big doughnut” in the sky before morphing into a “more conventional white puff of cotton.” “When most of the excitement was over, of course, the picture came in much better.” To make matters less interesting, the broadcast ended before American troops marched to ground zero, what would surely have been a recordable and exciting display of wargame maneuvering. For most viewers, writes Gould, “everything happened so fast—and so far away from the camera—that as a visual spectacle on TV the blast was a little anti-climatic.”2 [End Page 611] Networks were flooded with complaints after the fact. TV set owners, presuming the problem was a matter of fine tuning, attended more to the technology than the content of the broadcast itself, frantically changing channels and manipulating the horizontal and vertical hold knobs on their receivers. For such tinkerers, Gould speculates, “the atomic bomb meant geometric swirls, diagonal bars and their own large-screen trauma” (“Radio and Television,” 35). In Los Angeles, viewers could either look at the heavens or watch their TV sets. According to the Los Angeles Times, both options were disappointing. Gazing skyward at H-hour, one saw nothing but the “Southland morning haze”; on the tube, “a big black circle, and in the center a small white flash. Then slowly, like a giant rising from the earth, the fantastic mushroom cloud—a jagged lollipop on a narrow stick.”3 One hears in these descriptions the diminution of atomic expectation. Television, that centerpiece of the American living room, was a technology of counter-sublime abstraction, or worse, perhaps, domesticating the forces of nuclearism into cartoon figures of big donuts, jagged lollipops, and conventional white puffs of cotton. The Times assured readers that all stations would soon broadcast the extensive newsreel footage, for only emulsified film could translate television’s black blobs and squiggly lines into the event of nuclear detonation. But it could do so only belatedly.4 The problem of atomic disappointment predated this televisual blunder. According to Bob Mielke, the US Signal Corps deemed as only adequate the film coverage of the Trinity test, but “there was less satisfaction” with the bombing footage from Hiroshima and Nagasaki.5 In comparison to the eviscerating effects of the bomb on the ground, the image of the explosion itself was distant, brief, and shaky.6 To compensate for the paucity of this visual archive, the United States government amassed one and half million feet of film to document the 1946 tests, Operation Crossroads, at Bikini Atoll in the Marshall Islands, leading to a worldwide shortage of film stock and producing the most stunning images of mass destruction (Mielke, “Rhetoric and Ideology,” 29). Here, too the military was wracked by nuclear performance anxiety. The stated purpose of Operation Crossroads was to measure the impact of atomic explosions on naval vessels. Quoted in the New York Times, one scientist cautioned that, however spectacular the explosion, “damage to a large fleet spread...

Accurate Local Event Locations in Rock Valley, Nevada, Using a Bayesian Multiple‐Event Method

The Source Physics Experiment (SPE) is a series of chemical explosions at the Nevada National Security Site (NNSS, formerly the Nevada Test Site) designed to improve our understanding of explosion physics. A future SPE will place an explosion at the hypocenter of a small, shallow earthquake, providing a direct earthquake‐to‐explosion experiment. Candidate earthquakes for this novel experiment come from a sequence of over 200 unusually shallow events that occurred in Rock Valley, Nevada, in the southeastern portion of the NNSS during 1993. We apply the Bayesloc multiple‐event location algorithm (Myers et al. , 2007, 2009) to determine the best possible locations and depths for these events. Past nuclear tests in the nearby Yucca Flat on the NNSS are relocated with the same method to provide insight into the accuracy and uncertainties associated with the Bayesloc location results for the Rock Valley earthquakes. This test suggests that we can accurately pinpoint the location of the Rock Valley events within approximately 1 km of their true locations using direct arrival times only. The incorporation of differential arrival times and a potential ground‐truth event can significantly decrease the already small uncertainties associated with the epicenter locations. Depth determinations have uncertainties of a few kilometers. Depth uncertainty may be reduced by developing an accurate 3D model of P ‐wave and S ‐wave velocity for Rock Valley.