We study seismic noise recorded in the northeast of the Netherlands by
beamforming and by using empirical Green’s functions obtained by seismic interferometry.
From beamforming we found differences in noise directions in different frequency
bands. The main source region for primary microseisms (0.05–0.08 Hz) is in
the west-northwest direction, while the secondary microseisms (0.1–0.14 Hz) have a
west-southwest back azimuth. Furthermore, we observed a fast (~4 km/s) arrival
corresponding to the Rayleigh wave overtone. This arrival is also in the secondary
microseism band (between 0.15 and 0.2 Hz), but has a west-northwest back azimuth.
Both arrivals in the secondary microseism band gain in strength during winter, as does
the average wave height in the North Atlantic.We measured phase velocity dispersion
curves from both beamforming and noise cross-correlations, as well as group velocity
from the latter. These are then jointly inverted for an average 1D S-wave model. The
results show how the combination of different methods leads to a more complete characterization
of the propagation modes and an improved knowledge of the subsurface,
especially as the group velocity measurements increase the upper frequency limit of
analysis, providing valuable information of the shallowest subsurface