Development of analysis techniques for electromagnetic and electrical methods

The thesis stands as a pivotal contribution in the development of analysis techniques within the realm of Electromagnetic and Electrical methods, specifically delving into geological risks like landslides and levees. The urgency of this research is underscored by recent catastrophic events, including landslides and levee failures during floods, intensified by unforeseen and intense rainfall events that have raised concerns about the impacts of climate change. At its core, the thesis aims to comprehensively address and illuminate various facets of geophysics. Each chapter within the thesis serves a distinct purpose in advancing knowledge in the field. The methodological foundation of this thesis is multi-layered. One crucial facet involves the meticulous calibration of electromagnetic (EMI) data, a process specifically applied to segments of a levee subjected to multiarray EMI surveys. This calibration process is not merely a technical step but a strategic one, as it enables the transposition of the entire survey onto "ERT-like" images. This transposition is integral, enhancing the identification of vulnerabilities in river embankments, a critical aspect for averting potential failures that could have cascading consequences. Another pivotal aspect of the research involves the development of innovative self-potential (SP) survey techniques. This encompasses both conventional (Fixed-Base and Leapfrog) and non-conventional (Sparse Gradient and Full Sparse Gradient) arrays, reflecting a nuanced approach to data acquisition and analysis. Such an approach acknowledges the complexity of geological structures and strives to capture a comprehensive understanding through diverse survey techniques. The research unfolds with noteworthy findings that extend beyond the mere application of methodologies. It becomes evident that the use of new-concept instrumentations like FullWaver serves as a catalyst, facilitating detailed SP surveys with both conventional and unconventional arrays. The breakthrough realization emerges that meaningful SP values can be derived, even in scenarios involving stainless-steel electrodes. This finding is particularly significant, broadening the potential application of SP surveys, including data obtained from electrical resistivity tomography surveys. Moreover, the recoverable SP signal is showcased as not just a data point but a qualitatively useful insight. The exploration of the Amplitude Signal Analytic technique, when applied to the Sparse Gradient array, further enhances the arsenal of tools available for reconnaissance of the source of SP anomalies, marking a significant stride in the interpretative capabilities of SP data. In drawing conclusions, the ramifications of this study extend far beyond the academic realm. The thesis promises real-world impact with practical solutions and insights, addressing vulnerability identification, preventing river embankment failures, which might guide proactive measures against geological hazards.