Extracting subsurface information from ambient seismic noise – an example from Germany
Published in
SEG Houston 2009
Date of publication
29 October 2009
Abstract
We present results from a passive seismic survey carried out with broadband seismometers over an oil field in southern Germany. The aim was to analyze the ambient seismic noise spectrum in order to test for spectral signatures that may be indicative of variations in the subsurface. Variations in the naturally occurring background noise level happen at extremely low amplitude levels (typically between -120 to -180 dB [w.r.t. 1 m/s]), which oftentimes is orders of magnitudes lower than noise of anthropogenic origin that may be superimposed. In addition, the spatial, temporal and frequency-domain variability of cultural noise often exceeds the spatial and temporal variation of the natural background wave field. It is therefore critical to adequately remove any cultural noise contamination from the records before an attempt can be made at analyzing the ambient seismic noise level for any meaningful signatures of subsurface variations. Using a survey in an urban environment as an example, we present different methods to attenuate unwanted noise of anthropogenic origin. We show that, despite remnant contamination of the records by anthropogenic noise, we observe a statistically significant variation of the ratio between vertical and horizontal spectral amplitude (V/H) that can be used for subsurface characterization.
