Interpretation of the Estimated Green Function Extracted from Seismic Energy Generated by the North Sea Surf

By crosscorrelating and summing seismic energy measured at two receivers, one obtains an estimate of the Green function between those receivers. However, the reliability of the estimated Green function depends strongly on the characteristics and distribution of the seismic energy, used for the correlations. We show results from estimating the Green function using seismic energy recorded at the beach in Hoek van Holland, The Netherlands. Using passive data recorded with an areal array, we image the origin of the noise in the direction of the North Sea. In turn, this allows us to reliably interpret the crosscorrelation results in the direction perpendicular to the seashore as surface waves. This interpretation is confirmed by a comparison of active and passive data recorded with the same linear array perpendicular to the seashore. Both the main surface wave arrival and the dispersion show an excellent match. On the other hand, the correlation result in other directions cannot be interpreted as a surface wave. This is demonstrated using active data and correlation results of passive recorded with the areal array.