The geoelectric structure at the site of “Crystal” underground nuclear explosion ( Western Yakutia) from TEM data

Abstract

The resistivity pattern at the site of the “Crystal” underground nuclear explosion (Daldyn–Alakit district of Yakutia) of 1974 which led to an accident has been imaged using TEM data. The local background pattern corresponds to a three-or four-layer earth with a conductor at the base. The uppermost layer, with a resistivity of tens to hundreds of ohm · m, has its bottom at 190–260 m asl and consists of perennially frozen Late Cambrian carbonates. The resistivity structure of shallow subsurface at the blast epicenter remained unperturbed though being subject to mechanic and thermal effects. The bottom of the second layer is at 20 to 190 m below the sealevel and its resistivity is 7–10 ohm · m. It is composed of frost-bound and unfrozen cold rocks that belong to a Late Cambrian water-bearing sequence (an aquifer). The third and fourth layers make up the conducting base of the section (0.2–1.4 ohm · m) while the conductor’s top matches the table of a Middle Cambrian aquifer. Anomalous transient response at the site prompts the existence of a local conductor possibly produced by highly saline waters in the containment cavity and in deformed rocks around it. However, the resistivity is too low (0.02 ohm · m) to be accounted for by any model available at the present state of knowledge. Another problem is to explain how the brines circulating at large depths may have reached the explosion cavity and the surrounding strained zones. The study has provided a first idea of the background resistivity distribution and its UNE-induced changes.