Time lapse seismic monitoring of rock stress and fluid saturation changes in the near-surface following an explosive event at depth

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The primary goal of an OSI is to locate and characterise phenomena and observables that might indicate that a UNE has been conducted. Since this is a subsurface event, characterisation of an area of interest surrounding Surface Ground Zero (SGZ), and an understanding of potential paths of fluid migration through the geology, will maximise the chances of successful radionuclide (RN) sampling during an OSI. Since certain RN signatures are seen as the "smoking gun" of a nuclear test, this is highly desirable.The proposed project will be one of the first to explore the potential of Resonance Seismometry - a largely undefined and unexploited CTBT technique - to monitor this fluid migration. As such it will be world-leading and will have direct and tangible benefits for the treaty and for OSI. It will use advanced techniques in geophysical monitoring to assess the stress field in the subsurface and monitor fluid migration in the vicinity of SGZ. The technique proposed is known as 4D Seismic Monitoring, which uses high-precision equipment to detect minute changes in seismic velocity over time and space, which occur as a result of dynamic stress changes (cavity collapse and fracture propagation) or fluid migration (water table recovery) following a subsurface explosion.The project will have two complementary streams:-Definition of a parameter space in which the technique could be used effectively during an OSI. This will involve computational modelling of different geologies and source types to determine the stress field and predicted fluid migration, as well as the timescales over which these might be observed.-Optimisation of survey design given the limited time and manpower available during an OSI. This will include a study to determine equipment and data processing requirements. As part of this work, there will be a series of field trials in collaboration with petroleum industry partners.