Short-period seismic noise structure at the Norwegian Seismic Array

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Abstract
Power spectral analysis in frequency-wavenumber space and coherence studies in lag space have shown that the noise recorded by the short period Øyer subarray at NORSAR is critically dependent on the weather situation in the North Atlantic Ocean. In addition to the low-frequency noise from the west, there is observed 2-sec microseisms from the Baltic Sea. Because of the nonisotropic noise, the coherence is usually strongly azimuthal dependent, being represented in lag space by ellipses. Large time variations of the coherence are demonstrated.