Challenging assumptions: What correlation wavefields really look like…

https://cnrs.zoom.us/j/92691677923?pwd=QVVQaE9PTE9XQnZNeEhSSVRUSTNlUT09

ID de réunion: 926 9167 7923
Code secret: g2qk0z


Challenging assumptions: What correlation wavefields really look like…

Seismology originated as the study of earthquakes, motivated by their destructive impact on civilisations. Early on, seismologists realised that seismic wavefields emitted by earthquakes carry information about Earth's structure and allow to constrain its physical properties. In the past two decades, seismic wavefields emitted by sources other than earthquakes, such as ocean-land-interactions or man-made machinery, have been increasingly exploited to investigate Earth’s properties and their changes over time. Due to the complex nature of these wavefields, they have been historically discarded as “noise”. Under certain conditions, however, cross-correlation of these “noise" wavefields allows to estimate new wavefields (which we call correlation wavefields) travelling directly between seismic stations, removing the need to control or even know what the original sources of “noise” are or where they are located. These conditions are assumed to be met in nearly all studies that exploit ambient seismic noise. In this presentation, I will demonstrate that these conditions are violated in commonly used field data, including a large-N array of 5000 stations, how that can be understood theoretically, and what impact this may have on studies that aim to image or monitor Earth’s structure using ambient seismic noise.