Samuel Zappalá: Dual-Element Onshore Seismic Data Acquisition and Imaging Techniques: Case studies from Seoul metropolitan and Danish CCS sites

Abstract

This thesis presents the development of an innovative 2D reflection seismic acquisition system and its processing. The dual-element system integrates a nodal geophone array employed for deep imaging, and a MEMS-based landstreamer system employed for near-surface imaging, enabling high-resolution seismic data acquisition across multiple depth ranges. In the Korean Peninsula, where seismic activity has increased following the 2011 Tohoku-Oki earthquake, this system was applied to image crustal-scale fault systems. Three major systems were partially imaged, and the integration of the two datasets helped constrain fault locations in the densely populated, hard-rock environment of metropolitan Seoul, improving the understanding of seismic hazards and earthquake preparedness in the region. In Denmark, the system was employed for large-scale geological surveys to assess potential CO₂ storage structures, contributing to climate change mitigation efforts. A novel data merging technique was developed to integrate the two datasets, enhancing the imaging of reservoirs, seals, and fault structures. In addition, offshore sensors were considered and analysed to cover an onshore transition to offshore zone. The applied acquisition setup and developed merging technique were crucial to reach the desired resolution at all pertinent depths. A reflection-picked moveout correction processing step was developed for implementing high-resolution near-surface imaging through S-wave reflections as a by-product of large-scale acquisitions. The application of this method increased the reflection continuity in the stacked section that, complemented with velocity analyses, permitted the identification of key geological markers such as the water table depth and the top of the pre-Quaternary layers. Throughout the thesis, application of complementary analyses highlights the importance of leveraging different seismic data characteristics to improve subsurface imaging and geological reconstruction. The adaptability of this system demonstrates its effectiveness in complex environments, supporting both urban seismic risk mitigation and carbon capture and storage (CCS) applications. By addressing seismic hazards and climate challenges, this research underscores the crucial role of reflection seismology in tackling global environmental and societal issues.