On the Accuracy of Noise Tomography

In traditional earthquake tomography, seismologists use the travel time of waves from an earthquake to stations in order to determine the velocity structure of the Earth. A new technique allows similar travel time measurements to be made using ambient seismic noise recorded at pairs of stations. This 'noise tomography' technique is potentially very powerful since one does not need to rely on earthquakes and one can measure shorter period waves more easily.

However, the fact that the Earth has a non-uniform distribution of noise sources and has a non-uniform velocity structure complicates the noise tomography measurement in ways that have not been accounted for thus far. For example, the figure at right shows a comparison of a synthetic example in which a velocity anomaly exists between the pair of stations. For this case, there are significant differences between the expectation (assuming no velocity anomaly) and the actual measurement (Tsai, 2009). See publications section for more details.