Since it has already been demonstrated that point‐to‐point seismic propagation Green Functions can be extracted from seismic noise, it should be possible to image Earth structure using the ambient noise field. Seismic noise data from 148 broadband seismic stations in Southern California were used to extract the surface wave arrival‐times between all station pairs in the network. The seismic data were then used in a simple, but densely sampled tomographic procedure to estimate the surface wave velocity structure within the frequency range of 0.1–0.2 Hz for a region in Southern California. The result compares favorably with previous estimates obtained using more conventional and elaborate inversion procedures. This demonstrates that coherent noise field between station pairs can be used for seismic imaging purposes.

Turning noise into useful data-every geophysicist's dream? And now it seems possible. The field of seismic interferometry has at its foundation a shift in the way we think about the parts of the signal that are currently filtered out of most analyses-complicated seismic codas (the multiply scattered parts of seismic waveforms) and background noise (whatever is recorded when no identifiable active source is emitting, and which is superimposed on all recorded data). Those parts of seismograms consist of waves that reflect and refract around exactly the same subsurface heterogeneities as waves excited by active sources. The key to the rapid emergence of this field of research is our new understanding of how to unravel that subsurface information from these relatively complex-looking waveforms. And the answer turned out to be rather simple. This article explains the operation of seismic interferometry and provides a few examples of its application.A simple thought experiment. Consider an example of a horizontally stratified (one-dimensional) acoustic medium, and for the moment let us imagine that it has only a single internal interface. Now, say horizontally planar pressure waves are emitted by two impulsive sources, one after the other, and that one source is above the interface and one below. Vibrations from the resulting propagating waves are recorded at two receivers which can be placed anywhere between the two sources ( Figure 1, left).The recordings are shown in the center of the figure. At each receiver a direct and a reflected wave is recorded for source 1, whereas only one transmitted wave is recorded for source 2.Seismic interferometry of these data involves only two simple steps: The two recorded signals from each source are crosscorrelated and the resulting crosscorrelograms are summed (stacked). The result, shown on the right of Figure 1, is surprising; for positive times it is the seismogram that would have been recorded at either receiver if the other receiver had in fact been a source, and at negative times it is the time reverse of this seismogram. In other words, by this simple, two-step operation we have constructed the seismic trace from a virtual source-a source that did not exist in our initial experiment, and a source that is imagined to be at the location of one of our receivers.To generalize, this simple example placed no constraint on where the receivers were placed, provided they were between the sources. By moving either or both of them (or by using many distributed receivers from the start), it is therefore possible to construct the trace from an infinite number of virtual source and receiver pairs placed at any locations, by recording the signal from only two actual sources. What is more, provided one of the active sources is above the interface and receivers and the other is below, the location of the active sources is also arbitrary, and in order to carry out the process above we do not even need to know where these sources are. Seismic interferometry steps.The fundamental steps of t...

We construct a new seismic model for central and West Antarctica by jointly inverting Rayleigh wave phase and group velocities along with P wave receiver functions. Ambient noise tomography exploiting data from more than 200 seismic stations deployed over the past 18 years is used to construct Rayleigh wave phase and group velocity dispersion maps. Comparison between the ambient noise phase velocity maps with those constructed using teleseismic earthquakes confirms the accuracy of both results. These maps, together with P receiver function waveforms, are used to construct a new 3‐D shear velocity (Vs) model for the crust and uppermost mantle using a Bayesian Monte Carlo algorithm. The new 3‐D seismic model shows the dichotomy of the tectonically active West Antarctica (WANT) and the stable and ancient East Antarctica (EANT). In WANT, the model exhibits a slow uppermost mantle along the Transantarctic Mountains (TAMs) front, interpreted as the thermal effect from Cenozoic rifting. Beneath the southern TAMs, the slow uppermost mantle extends horizontally beneath the traditionally recognized EANT, hypothesized to be associated with lithospheric delamination. Thin crust and lithosphere observed along the Amundsen Sea coast and extending into the interior suggest involvement of these areas in Cenozoic rifting. EANT, with its relatively thick and cold crust and lithosphere marked by high Vs, displays a slower Vs anomaly beneath the Gamburtsev Subglacial Mountains in the uppermost mantle, which we hypothesize may be the signature of a compositionally anomalous body, perhaps remnant from a continental collision.