Ambient seismic noise and the North Sea

Project summary

Introduction

In the last decade, ambient seismic noise (ground motion generated by oceanic and atmospheric disturbances) has become key data for investigating the structure of the Earth’s crust. This project will investigate the potential of such data to image the crust beneath the whole of the North Sea, by exploiting seismograms recorded by stations located in surrounding countries, including the UK, Norway, Denmark, Germany and the Netherlands. A major challenge is optimising the signal processing and imaging methodology to maximize the extraction of structural information from an irregular distribution of ‘noise’ data. Findings from this project may galvanise a new breed of geophysical research in the North Sea (which has received relatively little attention outside of oilfield areas), and lead to a significantly improved understanding of the geology, tectonic history and earthquake potential of a major hydrocarbon producing region.

Project aims

The goal of the project is to examine the potential of ambient noise tomography to image the seismic structure of the crust beneath the North Sea in three dimensions (3-D). Previous work in this area has been limited, but does indicate that seismic surface waves experience unusually high attenuation as they propagate beneath the North Sea, such that signal can be difficult to extract and interpret from seismic recordings. High attenuation is also observed from earthquake generated surface waves propagating across the North Sea. In order to properly understand this phenomenon, and examine the extent to which useful seismic signal can be extracted for imaging purposes, our aim is to:

  • Obtain seismic recordings from as many broadband stations as possible that surround the North Sea.
  • Analyse the recordings to isolate the ambient noise signal, and attempt to spatially define the region of high attenuation within the North Sea in 2-D (map view), and then in 3-D (also in depth).
  • Apply cutting edge signal processing techniques to enhance the signal-to-noise ratio of the recorded ambient noise to allow for dispersion analysis.
  • Use an advanced Bayesian ‘transdimensional’ inversion method to construct a 3-D seismic shear velocity model of the region using all available ambient noise data, and interpret this model in combination with other local models (e.g., from the hydrocarbon industry) for structure and properties across the whole North Sea.