Advances in development of OSI geophysical techniques for mountainous environments

On-site inspection (OSI) is the final verification measure of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). According to paragraphs 69(e), 69(f) and 69(g) of Part II of the Protocol to the CTBT, an OSI may involve the following seismic and non-seismic geophysical techniques to search for, locate and characterize underground anomalies associated with a nuclear explosion: passive seismological monitoring for aftershocks; resonance seismometry and active seismic surveys; magnetic and gravitational field mapping; ground penetrating radar; and electrical conductivity measurements. In this presentation we review recent advances in development of OSI geophysical techniques, with a focus on the application of techniques in challenging mountainous environments. Previously, techniques were primarily tested in relatively flat or gently undulating terrain conditions.

Most recent advances in passive seismological monitoring include the upgrade of the telemetry system for data transmission and development of the data processing software to accommodate topographically challenging environments. To assess current OSI geophysical imaging capabilities for the other geophysical techniques and for deep site characterization applications in an integrated manner, an extensive OSI field test was conducted in the Austrian Ybbstaler Alps in September 2022. This was the first OSI field test in a challenging mountainous environment. Therefore, a number of operational, logistical and technical challenges had to be addressed. The implemented OSI geophysical techniques included resonance seismometry (passive seismic imaging) and active seismic surveys, magnetic and gravitational field mapping, as well as electrical conductivity measurements along three profiles over a cave system at 40-350 m depths mimicking underground cavities produced by an underground nuclear explosion. A newly acquired active seismic data recording system was tested for the first time, with the aim to mature OSI methods for active seismic surveys. Prior to this field test active seismic surveys have only been applied in a limited capacity. A recently developed concept of operations for resonance seismometry was also tested. Furthermore, based on the results of the field test, a new OSI workflow for gravitational field mapping is being developed. During the field test, full OSI data workflow for geophysical techniques was implemented using current functionalities within the Geospatial Information Management system for OSI (GIMO).

Overall, these recent advances in development of OSI geophysical techniques demonstrate the applicability of the full range of OSI geophysical techniques in mountainous terrain, and results of these projects will be used to further develop the geophysical techniques for challenging environments.