Assessment of Geohazards and Geodynamics by Integrated Gravimetric and Geodetic Methods

虽然可以使用一些地球物理和大地测量技术来评估地球灾害和地球动力学，但重力监测对于估计地下质量变化和运动特别有效，尽管其分辨率低且解决方案不是唯一的。然而，由于常规弹簧重力仪的灵敏度相对较低，机械弹簧的非线性漂移效应较大，在地质CO2储集地、油气藏和活动构造带对微小地下质量变化和运移的连续和长期监测的应用受到了限制。这些特征使对解释和分析至关重要的非周期重力信号的分析变得复杂。此外，重力仪记录结合了必须分离的地表变形和地下质量变化的重力效应。这些限制可以通过综合重力测量和大地测量技术来克服。超导重力仪采用磁悬浮球体作为测试质量，比弹簧式或绝对式重力仪具有更低的漂移和更高的时频灵敏度。有了这些属性，超导重力仪提供了精确和连续的重力变化记录，从时间到几十年的周期，这是监测地质灾害和地球动力学所需的。特别是，利用联合持久散射干涉合成孔径雷达(PSInSAR)雷达遥感和其他卫星和近地表大地测量技术(如测斜仪和全球导航卫星系统测量)精确模拟的地表变形约束，可以有效地将地下质量变化引起的重力分量与地面变形造成的重力分量分开。在这项研究中，我建议开发技术，通过综合重力和大地测量来评估微小和连续的质量变化和迁移。超导重力仪是测量时变重力的关键仪器，由绝对重力仪和弹簧重力仪支撑，用于四维重力和地下模拟。除了地下质量的变化和移动，重力测量还包括与地下活动有关的地表变形产生的重力效应。为了分析位移，InSAR技术将与重力相结合。开发的技术将用于监测：1)卑诗省温哥华岛附近卡斯卡迪亚俯冲带的同震和静默地震形变；以及2)阿尔伯塔省和萨斯喀彻温省地质二氧化碳储存点注入的二氧化碳的迁移和泄漏。尽管该地区的构造事件在地球表面是沉默的，因为它们不会造成任何明显的破坏，但它们将使我们更好地估计加拿大西海岸下一次大地震。这一活跃的构造带目前正在积累应力，最终可能会引发一场大地震，随后引发海啸。这些地质灾害会造成人员伤亡和财产损失。如果可以检测到大地震的前兆，这些前兆可以用于公共安全和政策制定。在确保地质碳储存方面，对储存中的二氧化碳羽流进行定量追踪并检测通过盖层或含水层的任何泄漏是非常重要的，因此，需要一项全面的监测协议来确保碳储存的安全。这项研究可能是唯一一项满足上述要求的研究：监测地下储存的质量变化、质量移动和泄漏。

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.