Seasonal Variability of Microseism Sources: Characterization and Impact on Noise Correlation

Abstract

Microseisms are the most persistent and continuous seismic signals on Earth, generated primarily by oceanic processes. These signals arise from two distinct mechanisms, defining the link between primary and secondary microseisms. Previous research has demonstrated that continuous seismic noise records can be effectively used to extract information about the Earth’s subsurface. Specifically, cross-correlation of ambient seismic noise between two stations allows for the approximation of Green’s function, offering insights into seismic wave propagation.

A key focus of this thesis is the characterization of microseism sources from multiple perspectives. First, we investigate their contribution to cross-correlation wavefields between station pairs, addressing the question of whether microseisms influence the coda of correlation wavefields. Our findings confirm that oceanic source regions and their seasonal variations are imprinted throughout the coda, challenging the conventional assumption that the coda consists purely of scattered waves. This suggests a need to reconsider how coda waves are interpreted in noise-based seismic applications.

Another major aspect of this research is the improved understanding of microseism sources and their generation mechanisms. Using well-established three-component seismic array beamforming, we analyze the locations of dominant Rayleigh and Love wave microseism sources in two different regions, the United States and Europe across both primary and secondary microseism bands. Additionally, with the increasing demand for full ground motion analysis, we evaluate the potential of array-derived rotation methods for microseism studies. A comparative analysis suggests that array-derived rotation can be effectively applied to microseism source characterization. By examining the regions of study in the United States and Europe, this research further explores the distinct microseism generation mechanisms of the North Pacific and North Atlantic Oceans. These findings are particularly relevant for future developments in seismic monitoring based on microseism recordings.