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.