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Summary. On-site inspections (OSIs) constitute the final verification measure under the ComprehensiveNuclear-Test-Ban Treaty (CTBT). OSIs are launched to establish whether or not a nuclear explosion has beencarried out. During such an inspection, facts are gathered within a limited investigation area of 1000 km2. Timeis one of the challenges that an inspection team has to face when conducting an OSI. Other challenges are thesize of the team – which is limited to 40 inspectors - and Treaty limitations on the use of allowed techniques. TheIntegrated Field Exercise (IFE08) conducted in 2008 in Kazakhstan was the first large-scale on-site inspectionexercise ever conducted by the CTBT Organization (CTBTO). The exercise took place in a steppe south east ofKurchatov, within the former Soviet Union’s Semipalatinsk nuclear test site. In this poster we provide anoverview of the geophysical surveys conducted by a subteam of ten geophysicist members of the inspection teamduring IFE08 in order to collect evidence of a hypothetical nuclear test explosion. The geophysical data collectedduring IFE08 (following radiological protection standards), especially ground and aerial magnetic data as well asresistivity data, form the basis for an invaluable database to be used by the CTBTO in the future for a betterunderstanding of the phenomenology related to an underground nuclear explosion (UNE).
Geophysical activities (excluding passive seismic) allowed by the Comprehensive Nuclear-Test-Ban Treaty (Protocol, Part II, Paragraph 69)
[underlined: activities carried out during IFE08]- Resonance seismometry and active seismic surveys to search for and locate
underground anomalies, including cavities and rubble zones;- Magnetic and gravitational field mapping, ground penetrating radar and electrical conductivity measurements at the surface and from the air, as
appropriate, to detect anomalies or artifacts;- Drilling to obtain radioactive samples
2 CPT subteam during IFE08. Front, Rainier Arndt (subteam leader). Behind, from left to right, Ales Fronka (RN subteam), Zsolt Pronai, George Tuckwell (deputy subteam
leader), Samuel Toon, Dmitry Sagaradze, Andrew Katumwehe, Bing Gong, Luis Gaya-Piqué, Matthew Purss, and Ashley Grant
Goal of the subteam: to clarify the nature of the triggering event by collecting geophysical data related either to the event itself (e.g. geological changes) or
to the preparation of a potential site (e.g. anthropogenic signatures).
Resistivity profiles. Instrumentation: Syscal Pro Switch 72.Left: resistivity model for dipole-dipole survey over Bh 129. Watertable is at a depth of approx. 5m. The deflection close to the locationof the borehole may be due to any down-hole test modifying the localhydrogeology. A higher resistivity layer is present at a depth of 25m.This layer has a lower electrical resistivity at the borehole location.To the south-east of the borehole there is a lower resistivity featureindicative of a plume of material, either conductive fluids or metalleaching from the borehole itself. An associated magnetic signaturesuggests a ferrous component; therefore a preliminary hypothesis isthat the plume is a zone of “staining” by iron oxide from the boreholecasing. This would suggest that the borehole has been in place for anumber of years, with significant modification of the ground waterchemistry as a result of a UNE in the past.
Aeromagnetics. Data was acquired over a 5hr-long flight, 100mflight line spacing and altitude of 100m above ground level.Instrumentation: GPS, laser altimeter, magnetometer ScintrexCS-2 towed 30m below the helicopter, and an airborne GIS.Below: analytic signal of aeromagnetic data. Most of the visiblemagnetic signatures were attributed to geological units. However,some short wavelength magnetic anomalies warrant furtherground investigation to determine their origin.
Ground magnetics. This technique showed its capability during IFE08 to detect themagnetic signature from cased boreholes or similar vertical metallic structures.Instruments used: Geometrics G-858 (gradiometer configuration) and GemSys GSM-19.The amplitudeof the anomalies are consistent with those obtained from forward models.
Total magnetic field reduced to the pole over abandoned Bh130. Data were recorded on random walk (empty circles) around the borehole (solid circle). Instrument: GSM-19.
Total magnetic field reduced to the pole over abandoned Bh 3001 (solid circle). Instrument:
G-858.
Total magnetic field over abandoned Bh 129 (solid circle). Small circles: metallic objects on
the surface. Instrument: G-858.
N
Ground penetrating radar. Instrumentation: MalåGeoscience with shielded/unshielded antennas from 50 to500MHz. GPR showed few subsurface features with weakreflections that suggest the locations of former infrastructure,trenches, etc. Reflections are weak enough to suggest that theinfrastructure, if once present, was removed long ago.Below: ground penetrating radar time slice around Bh 3001.
Conclusions. For the CPT subteam, IFE08 was an exceptional opportunity to work at a former nuclear test site. The team ofgeophysicists was able to observe some relevant phenomenology in the field and identify a number of geophysical signatures of OSIrelevance. The data collected during IFE08, together with data from previous activities, form the basis of an invaluable database tobe used for OSI training and for a better understanding of the geophysical signatures associated with UNE.
Geophysical Techniques for On-Site Inspections – Experienceand OverviewLuis R. Gaya-Piqué1, Rainier Arndt1 and IFE08 CPT subteam2
1On-Site Inspection Division, CTBTO PrepCom, Vienna International Centre, P.O. Box 1200, A-1400, Vienna, Austria, e-mail: [email protected], [email protected]
