The origin of Love waves in the ocean generated noise wave field

• Applicant: Professorin Dr. Céline Hadziioannou
• Subject Area: Geophysics
• Term: from 2013 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 238116732

Noise correlations have revolutionized seismology. They make it possible to exploit the vast amounts of background noise recorded continuously around the world. In a way, they allow us to exploit seismic noise to perform earthquake-free seismology. The resulting explosion of high-resolution tomographic images in the past decade provides us with better event locations, better strong motion predictions and a deeper understanding of crustal dynamics. All of these have important implications for natural hazard management.Noise correlations have also been used successfully to monitor wave speed changes over time in potentially dangerous structures such as landslides, volcanoes and active fault zones. Most of the applications so far have concentrated on the vertical component records, but recently more interest arises to include the information contained in the horizontal components.However, as the methods employed are developed and become more accurate, their drawbacks are becoming more apparent. One of the problems in noise correlation, is that the resulting “Green’s function” does not only carry the wanted information about the propagation medium, but also about the noise sources. Therefore, to improve the noise correlation technique, it is important to have a good understanding of the noise sources and their behavior. The sources of the vertical component motion in microseismic Rayleigh waves are already widely studied, while those for the horizontal shear motions in Love waves remain relatively unexplored. This proposal aims at characterizing and understanding Love waves in ambient seismic noise, and their contribution to noise correlation methods. Several fundamental questions are addressed:• How are microseismic Love waves generated?• Where are Love waves generated? What are the geographic differences compared to Rayleigh wave generation areas?• How much energy do Love waves contribute to seismic noise? How does this depend on the frequency?• When are the strongest Love waves generated? Does their frequency content change over time?The current applications of noise correlations are all in some way influenced by the spatial and temporal behavior of ambient noise sources. Deeper understanding of microseismic Love wave generation will therefore benefit the noise correlation community by bringing better images of crustal structure and more accurate monitoring methods within reach. This project aims to improve noise correlation results by understanding the underlying noise sources. This will be done by combining a data-driven characterisation of Love wave noise sources with numerical simulations of Love wave generation.

• DFG Programme: Independent Junior Research Groups