Seismic noise subsoil in order to draw seismic microzonation maps showing the predicted ground response to earthquakes. Research on the origin of seismic noise indicates that the low frequency part of the spectrum (below 1 Hz) is due to natural causes, chiefly ocean waves. In particular the peak between 0.1 and 0.3 Hz is clearly associated with the interaction of water waves of nearly equal frequencies but opposite directions. At high frequency (above 1 Hz), seismic noise is mainly produced by human activities such as road traffic and industrial work; but there are also natural sources, like rivers. Around 1 Hz, wind
Seismic interferometry location. Seismic interferometry can virtually move a source into a downhole location to better illuminate and capture steeply dipping sediments on the flank of a salt dome. In this case, the SI result was very similar to that obtained using an actual downhole source. Seismic interferometry can locate the position of an unknown source and is often utilized in hydrofrac applications to map the extent of induced fractures. It is possible that interferometric techniques can be applied to timelapse seismic monitoring of subtle changes in reservoir properties in the subsurface. Seismic interferometry applications are currently limited by a number of