Assessment of Geohazards and Geodynamics by Integrated Gravimetric and Geodetic Methods

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Although assessments of geohazards and geodynamics are possible with a number of geophysical and geodetic techniques, gravity monitoring is especially effective for estimating subsurface mass change and movement despite its low resolution and non-unique solution. However, applications of the gravimetric method have been limited for continuous and long-term monitoring of minute subsurface mass change and migration at geological CO2 storage sites, hydrocarbon reservoirs and active tectonic zones, mainly because conventional spring gravimeters suffer from relatively low sensitivity and the large nonlinear drift effects of the mechanical springs. These characteristics complicate the analysis of the non-periodic gravity signals that are vital for interpretation and analysis. In addition, the gravimeter records combine the gravity effects of surface deformation and subsurface mass change that must be separated. These limitations can be overcome by integrated gravimetric and geodetic technologies. The superconducting gravimeter, which uses a magnetically levitated sphere as a test mass, has considerably lower drift and much higher sensitivity in the time and frequency domains than spring or absolute gravimeters. With these attributes, the superconducting gravimeter provides precise and continuous records of gravity variations over times to periods of decades that are required for monitoring geohazards and geodynamics. In particular, the gravity components from subsurface mass changes can be effectively separated from those caused by the surface deformations using surface deformation constraints accurately modelled from combined Persistent Scatterer Interferometric SAR (PSInSAR) radar remote sensing and other satellite and near-surface geodetic technologies, such as inclinometer and GNSS measurements. In this research, I propose to develop techniques to assess minute and continuous mass change and migration continuously by integrated gravimetric and geodetic measurements. The superconducting gravimeter is a key instrument for measuring the time-varying gravity, which is supported by absolute and spring gravimeters for 4D gravity and subsurface modelling. In addition to subsurface mass change and movement, the gravity measurements include the gravity effects from surface deformations associated with the subsurface activities. To analyze the displacement, InSAR technology will be integrated with gravity. The developed techniques will be applied to monitor: 1) co-seismic and silent earthquake deformation in the Cascadia subduction zone near Vancouver Island, BC; and, 2) migration and leakage of injected CO2 at Alberta and Saskatchewan geological CO2 storage sites. Although the tectonic events in this zone are silent on the Earth’s surface, in that they do not cause any noticeable damage, they will lead us to better estimates of the next great earthquake on the west coast of Canada. This active tectonic zone is currently accumulating stress that may eventually cause a great earthquake followed by a tsunami. These geohazards will cost human lives and cause property damage. If the detection of precursors of a major earthquake is possible, these precursors can be used for public safety and policy making. In terms of securing geological carbon storage, the tracking of the CO2 plume quantitatively in the storage and the detection of any leaks through the caprocks or aquifers are very important, and, hence, a comprehensive monitoring protocol is required for secure carbon storage. This research may be the only one that meets the above requirements: monitoring subsurface mass change, mass movement and leakage from the subsurface storage.