Shallow Permafrost at the Crystal Site of Peaceful Underground Nuclear Explosion (Yakutia, Russia): Evidence from Electrical Resistivity Tomography

The site where a peaceful underground nuclear explosion, Crystal, was detonated in 1974, at a depth of 98 m in perennially frozen Cambrian limestones, was studied by electrical resistivity tomography (ERT) in 2019. The purpose of our research, the results of which are presented in this article, was to assess the current permafrost state at the Crystal site and its surroundings by inversion and interpretation of electrical resistivity tomography (ERT) data. Inversion of the ERT data in Res2Dinv verified against ZondRes2D forward models yielded 2D inverted resistivity sections to a depth of 80 m. The ERT images revealed locally degrading permafrost at the Crystal site and its surroundings. The warming effect was caused by two main factors: (i) a damage zone of deformed rocks permeable to heat and fluids, with a radius of 160 m around the emplacement hole; (ii) the removal of natural land cover at the site in 2006. The artificial cover of rock from a nearby quarry, which was put up above the emplacement hole in order to prevent erosion and migration of radionuclides, is currently unfrozen.

ECOLOGICAL CONSEQUENCES OF THE UNDERGROUND NUCLEAR EXPLOSION IN KHARKIV REGION

The article covers an event that has been hidden for fifty years, namely the failure of a nuclear explosion at Kharkiv region. The possible ecological consequences of the mentioned event are analyzed. Data from different sources are compared for further planning of researches of an ecological condition of district. The basis for creating a system for studying the environmental consequences of a nuclear explosion at the time of its implementation and at present is provided. The basics of standard calculations of probable exposure of the population, which had to be carried out immediately after the explosion, are provided, and systemic recommendations for further environmental control in the designated area are offered.

THE ELECTROTOMOGRAPHY SURVEY IN DIFFICULT GEOTECHNOGENIC CONDITIONS AT THE PEACEFUL UNDERGROUND NUCLEAR EXPLOSION "CRYSTAL" SITE

The paper presents the results of measurements in 2019 by electrotomography at the site of the emplacement hole of the peaceful underground nuclear explosion "Crystal", carried in 1974 at a depth of 98 m in permafrost Cambrian carbonate rocks, and the neighboring forest area. The fence made of metal poles and barbed wire around the site, and the buried fragments of the casing of the emplacement hole create significant interference of measurements. To avoid the electromagnetic noise, the measured data of the apparent electrical resistivity was cleaned manually. Data inversion was performed in the Res2Dinv program. Geoelectric models, namely two-dimensional sections of the upper part of the geological environment to a depth of up to 80 m, were obtained. To verify the models, forward modeling was performed using the ZondRes2D program.

FIRST RESULTS OF STUDY OF ISOTOPE COMPOSITION OF URANIUM IN WATER SAMPLES OF THE “CRYSTAL” SITE

The first results of isotope composition of uranium of surface water of the peaceful underground nuclear explosion “Crystal” site are discussed. The isotope ratio is determined by the mass-spectrometry on the inductively coupled plasma.

The analysis of natural radionuclides activity in the soil and vegetation cover in the South of the Tyumen Region

The paper deals with the study of the radiation state of the soil and herbaceous vegetation represented by perennial grasses (Poa pratensis, Calamagrostis epigejos, Rubus saxatilis, Carex acuta, Phleum pratense) in the south of the Tyumen Region. The content and distribution of natural radionuclides in soil and herbaceous vegetation was studied in the Nizhnetavdinsky District of the Tyumen Region at the site of an underground nuclear explosion. Sampling and laboratory tests were carried out according to generally accepted methods. Soil samples were taken at the epicenter of the explosion and at the cardinal directions. Layer-by-layer sampling allowed us to study the vertical distribution of radionuclides in the soil profile. Sampling of perennial grasses was carried out at the same sampling points. Radiation studies of soil and vegetation samples were carried out on the Progress-2000 spectrometric complex. The authors have revealed specific activity of natural radionuclides (K-40, Th-232 and Ra-226) in the profile of grey forest soil in the Nizhnetavdinsky District. They have calculated effective specific activity of radionuclides in the soil. The comparative analysis of the obtained results with the data on administrative areas in the south of the Tyumen Region showed that in the soil of the Nizhnetavdinsky District specific activity of natural radionuclides is higher than in the South region in general. The specific activity of natural radionuclides in perennial grasses of the Nizhnetavdinsky District was determined, and the coefficient of accumulation of radionuclides was calculated.

Dense Seismic Array Study of a Legacy Underground Nuclear Test at the Nevada National Security Site

ABSTRACT The complex postdetonation geologic structures that form after an underground nuclear explosion are hard to constrain because increased heterogeneity around the damage zone affects seismic waves that propagate through the explosion site. Generally, a vertical rubble-filled structure known as a chimney is formed after an underground nuclear explosion that is composed of debris that falls into the subsurface cavity generated by the explosion. Compared with chimneys that collapse fully, leaving a surface crater, partially collapsed chimneys can have remnant subsurface cavities left in place above collapsed rubble. The 1964 nuclear test HADDOCK, conducted at the Nevada test site (now the Nevada National Security Site), formed a partially collapsed chimney with no surface crater. Understanding the subsurface structure of these features has significant national security applications, such as aiding the study of suspected underground nuclear explosions under a treaty verification. In this study, we investigated the subsurface architecture of the HADDOCK legacy nuclear test using hybrid 2D–3D active source seismic reflection and refraction data. The seismic data were acquired using 275 survey shots from the Seismic Hammer (a 13,000 kg weight drop) and 65 survey shots from a smaller accelerated weight drop, both recorded by ∼1000 three-component 5 Hz geophones. First-arrival, P-wave tomographic modeling shows a low-velocity anomaly at ∼200 m depth, likely an air-filled cavity caused by partial collapse of the rock column into the temporary postdetonation cavity. A high-velocity anomaly between 20 and 60 m depth represents spall-related compaction of the shallow alluvium. Hints of low velocities are also present near the burial depth (∼364 m). The reflection seismic data show a prominent subhorizontal reflector at ∼300 m depth, a short-curved reflector at ∼200 m, and a high-amplitude reflector at ∼50 m depth. Comparisons of the reflection sections to synthetic data and borehole stratigraphy suggest that these features correspond to the alluvium–tuff contact, the partial collapse cavity, and the spalled layer, respectively.

The Finite-interval Spectral Power method for detecting underground cavities using seismic ambient noise

SUMMARY Undetected natural and man-made cavities pose a serious geotechnical hazard to human safety. It is therefore important to develop methods for identifying and locating underground cavities in urban development and civil construction. Another important type of cavity is the one generated by an underground nuclear explosion. Identification and location of such cavities is an important proof in case of suspicion of violating the Comprehensive Nuclear-Test-Ban Treaty (CTBT), an international treaty banning nuclear weapon test explosion or any other nuclear explosion which is yet to come into force. We present a new method for detecting and locating a horizontal position of cavity which uses the Finite-interval Spectral Power of seismic ambient noise. The method makes it possible to use single-station measurements at a set of potentially irregularly distributed points in the area on the Earth's free surface over a suspected cavity. Because the method gives better results for undistorted segments of noise records, we also present a method of automatic identification of such segments. We tested our method using records of noise from a site near the Felsőpetény, Hungary, which were collected for the CTBT Organization during a field test in the framework of developing on-site inspection capabilities. The method is ready for further tests in different cavity conditions and applications.

Quantitative assessment to the impact of InSAR ionospheric and tropospheric corrections on source parameter modelling: application to the 4th nuclear test, North Korea

SUMMARY Although many studies have revealed that the atmospheric effects of electromagnetic wave propagation (including ionospheric and tropospheric water vapour) have serious impacts on Interferometric Synthetic Aperture Radar (InSAR) measurement results, atmospheric corrections have not been thoroughly and comprehensively investigated in many well-known cases of InSAR focal mechanism solutions, which means there is no consensus on whether atmospheric effects will affect the InSAR focal mechanism solution. Moreover, there is a lack of quantitative assessment on how much the atmospheric effect affects the InSAR focal mechanism solution. In this paper, we emphasized that it was particularly important to assess the impact of InSAR ionospheric and tropospheric corrections on the underground nuclear explosion modelling quantitatively. Therefore, we investigated the 4th North Korea (NKT-4) underground nuclear test using ALOS-2 liters-band SAR images. Because the process of the underground nuclear explosion was similar to the volcanic magma source activity, we modelled the ground displacement using the Mogi model. Both the ionospheric and tropospheric phase delays in the interferograms were investigated. Furthermore, we studied how the ionosphere and troposphere phase delays could bias the estimation of Mogi source parameters. The following conclusions were drawn from our case study: the ionospheric delay correction effectively mitigated the long-scale phase ramp in the full-frame interferogram, the standard deviation decreased from 1.83 to 0.85 cm compared to the uncorrected interferogram. The uncorrected estimations of yield and depth were 8.44 kt and 370.33 m, respectively. Compared to the uncorrected estimations, the ionospheric correction increased the estimation of yield and depth to 9.43 kt and 385.48 m, while the tropospheric correction slightly raised them to 8.78 kt and 377.24 m. There were no obvious differences in the location estimations among the four interferograms. When both corrections were applied, the overall standard deviation was 1.16 cm, which was even larger than the ionospheric corrected interferogram. We reported the source characteristics of NKT-4 based on the modelling results derived from the ionospheric corrected interferogram. The preferred estimation of NKT-4 was a Mogi source located at 129°04′22.35‘E, 41°17′54.57″N buried at 385.48 m depth. The cavity radius caused by the underground explosion was 22.66 m. We reported the yield estimation to be 9.43 kt. This study showed that for large-scale natural deformation sources such as volcanoes and earthquakes, atmospheric corrections would be more significant, but even if the atmospheric signal did not have much complexity, the corrections should not be ignored.

Chemical composition of surface water of the “Crystal” site and uranium content in it in 2019

The chemical composition of surface and ground water of the site of the underground nuclear explosion “Crystal” in 2019 is discussed. Methods of atomic emission spectrometry, titrimetry and capillary electrophoresis are used in the work. The content of uranium is determined by mass–spectrometry on inductively coupled plasma. The direct correlation between contents of uranium and sulphates anions probably indicates of degradation of the cement filling of the emplacement hole.

Magnetic survey at the "Crystal" site in 2019

The paper discusses the results of magnetic survey over the site of the "Crystal" underground nuclear explosion, which indicated that large metal objects are buried under the sarcophagus. These results will help in interpreting data of other geophysical methods used here to study the effect of the underground nuclear explosion on the geological environment.