Recent advances in seismic methods make use of coherent signal recorded at a pair of stations to image the underlying structure without the use of earthquakes or explosions. This low amplitude seismic “noise” present at all seismic stations is generated from a wide range of sources like waves and wind along shorelines to local man-made activities such as cars, trucks, and trains. It is known as “Ambient Noise”, noise in the background. By cross correlating long time series between stations, the common signal is retrieved while the incoherent energy cancels out. This leaves a signal that reveals information about seismic velocity between the two seismometers. By making measurements on these signals and using an array of stations for many ray paths, a three-dimensional image of the subsurface shear velocity can be determined. This method is known as Ambient Noise Tomography (ANT for short).
Ambient Noise Tomography opens up new possibilities in imaging the subsurface at many different scales and complements traditional passive source tomography. Seismic imaging without the earthquakes! ISTI seismologists are experts in using ANT to decipher the subsurface velocity structure beneath your region of interest. Contact us today for a quotation.
Below is a PDF of a workflow for ANT data processing: