The ROMY ring laser array for seismology

Brotzer, Andreas (2025): The ROMY ring laser array for seismology: instrumental characterization, low noise limits for rotations and seismological applications. Dissertation, LMU München: Fakultät für Geowissenschaften

Abstract

The field of rotational seismology emerged after advances in ring laser gyroscope (RLG) technology made it possible to observe weak rotational ground motions in seismic wavefields. Large-scale RLGs are challenging to operate, but are currently the only possibility to resolve small rotational motions associated with phenomena in seismology and geodesy, such as the Earth’s free oscillations or variations of the Earth’s rotation vector. The ROMY ring laser array is an unprecedented instrument for geoscientific observations. By combining four large-scale, triangular-shaped RLGs with high sensitivity, it can provide all three components of weak rotational ground motion. As part of this thesis, the performance and operational stability of ROMY has been evaluated and improved through various hardware upgrades. For all heterolithic RLGs, a profound understanding of environmental impacts and their mitigation or correction is essential. Therefore, a network of environmental monitoring sensors has been developed and installed for ROMY. This enabled the identification and quantification of instrumental effects caused by environmental influences, such as temperature changes. The first rotational low noise model was derived and validated with available direct and indirect rotational observations of RLGs and seismic arrays, respectively. Knowledge of the rotational background noise floor contributes to a deeper understanding of our planet and provides a valuable guidance for instrument development. Unique direct observations of ground tilt by ROMY allow the study of ground deformation induced by atmospheric processes at long periods, independent of inertial acceleration contributions. In combination with local barometric pressure observations, compliance functions are obtained and a low noise level at long periods, which is imposed by atmospheric pressure changes, is determined for ROMY. Successfully operating three RLGs continuously over one year resulted in a valuable dataset. While this dataset acquired with ROMY is used to demonstrate potential six degree-of-freedom (6 DoF) applications, such as seismic source tracking of the secondary microseism, a one-year dataset of a portable 6 DoF station in southern California is used to analyze local and regional seismicity and derive an empirical scaling relation for ground rotations. Although continuous operation has been demonstrated, further hardware upgrades for ROMY, in order to mitigate identified instrumental effects and enhance the operational stability, are encouraged. Harnessing ROMY’s full potential will ultimately provide the observational basis to study and answer many open geoscientific questions.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: rotational seismology, ring laser, romy, rotational low noise limit, seismology
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften
• Fakultäten: Fakultät für Geowissenschaften
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 5. Februar 2025
• 1. Bericht­erstatter:in: Igel, Heiner