Abstract
Spatial geodesy has become an indispensable tool in contemporary geophysical research, offering excellent precision and stability. By integrating Global Navigation Satellite System (GNSS) data with Interferometric Synthetic Aperture Radar (InSAR) observations, researchers can quantitatively characterize Earth's crustal motion and deformation. However, the application of these observations in tectonically active regions, such as subduction zones and major fault systems, reveals limitations due to the complex and multifaceted nature of fault dynamics. To address these challenges, the combination of spatial geodesy with numerical simulations and high-precision monitoring technologies, such as tiltmeters and strainmeters, effectively bridges the gaps inherent in spatial geodesy. This integration provides deeper insights into dynamic mechanisms and offers complementary methods for identifying subtle surface deformations caused by fault behavior.This thesis, the result of the joint doctoral program between the Institute of Tibetan Plateau Research of the Chinese Academy of Sciences and the University of Montpellier, focuses on two key objectives: (1) combining numerical simulations and geodetic data to investigate dynamic mechanisms, and (2) developing innovative methods for precise optical borehole tiltmeter (OBT) orientation calibration and transfer function calculation to obtain accurate ground data. The specific contributions of this research are as follows:1.This thesis highlights the effectiveness of numerical simulations in exploring the fault mechanics of the southeastern Tibetan Plateau. The results reveal that the low frictional strength and the distinctive big-bend geometry of the Xianshuihe-Xiaojiang fault system play critical roles in shaping regional strain distribution, influencing activity within the Mabian fault zone out of the Tibetan Plateau. Additionally, the Anninghe-Zemuhe fault is considered as the main boundary regulating relative motion between the southeastern Tibetan Plateau and the South China block. These insights not only enhance our understanding of regional seismic behavior but also provide essential data for future earthquake risk assessments.2.The thesis also addresses challenges in high-precision tiltmeter data acquisition through an innovative OBT azimuthal calibration method based on tidal correlation calculations. This method optimizes azimuth by maximizing the correlation between recorded tilt data and theoretical tidal signals. It demonstrates consistent efficacy across various datasets and shows promise for application in other tidal phenomena recording instruments, such as strainmeters and seismometers, particularly in challenging measurement environments. Furthermore, to mitigate distortions from instrument-crust coupling, a comparative method utilizing nearby calibrated instruments is proposed. This method calculates transfer function parameters by minimizing discrepancies between theoretical and operational transfer functions, enabling the accurate retrieval of accurate ground motion signals. The OBT's higher stability and signal-to-noise ratios, particularly in detecting Earth's free oscillation modes, further underscore its utility for long-term Earth motion monitoring.In conclusion, this thesis integrates geodesy with numerical simulation techniques to deeply investigate the geodynamic mechanisms in the seismically active region of the southeastern Tibetan Plateau. It also proposes innovative methods for azimuthal and instrument-crust coupling calibrations, significantly improving the precision of ground motion data. These findings not only deepen our understanding of seismic mechanisms but also establish a robust scientific foundation for future earthquake prediction and risk assessment.