Estimating the Geological Structure and Transport Properties of Denied and Limited Access Sites

• Published in: Earth and space science (Hoboken, N.J.) N.J.), 2022-10, Vol.9 (10), p.n/a
• Main Authors: Duncan, N. A., Deinert, M. R.
• Format: Article
• Language: English
• Subjects: denied access; Estimates; Fractals; Fractionation; Gases; Geological structures; Geology; Isotope fractionation; limited access; Methods; Military supplies; nuclear test; Nuclear tests; Nuclear weapons; Permeability; Pore size; Porosity; Rocks; Seismology; subsurface
• ISSN: 2333-5084; 2333-5084
• DOI: 10.1029/2022EA002543

Onsite measurements are the standard for establishing geological conditions and related transport properties. However, making direct measurements is not always possible, either because a location is too remote, too vast, or access is outright denied. The latter is typically the case at nuclear test sites, or military installations. Here we describe a systematic method to characterize geology and estimate fracture width, spacing, tortuosity, permeability, and porosity at locations where direct measurements cannot be made. Fractures are treated as fractals with their respective fractal dimensions determined using surface images. Tortuosity in the geological matrix (i.e., bulk media) is determined using rock class with the latter also being used to determine distributions for permeability and porosity. The approach is tested using areal images and rock class for the Nevada Test Site and validated by comparison to field and core measurements. Past work has shown that testing a nuclear weapon underground can affect not only the migration time for gases to the surface but also their isotopic ratios. Accurately modeling gas transport and isotopic fractionation requires knowledge of the geology. However, suspected tests are typically conducted at sites to which the international community has no access. Plain Language Summary Subsurface geology affects processes that affect aquifer recharge, land‐atmosphere gas transport, seismic conditions and stability. Onsite measurements are the standard for establishing the geological conditions at a particular location. However, accessing a location is not always possible and in situations like these, other methods with which to estimate subsurface conditions are needed. This is particularly true for the sites at which suspected nuclear tests take place, or other locations to which access is restricted. Here we provide a systematic way for estimating the geology at such locations that is based on open source data. Key Points It is not always possible to gain access to a site where understanding the local geology is important We provide a systematic way to estimate fracture width, spacing, tortuosity, permeability, and porosity using areal images and rock class The approach is validated with an analysis of the Nevada Test Site and comparison of the results to field and core measurements