Lapo Boschi (Institut des Sciences de la Terre de Paris). U​nderstanding noise: seismic and acoustic interferometry in the laboratory and in the field.

The cross correlation of ambient signal allows seismologists to collect data even in the absence of seismic events (earthquakes or explosions). “Seismic interferometry” shows that the cross correlation of simultaneous recordings of a random ("diffuse") wave field made at two locations is formally related to the impulse response between those locations. This idea has found many applications in seismology, as a growing number of dense seismic networks become available: cross-correlating long seismic records, the Green’s function between instrument pairs is “reconstructed” and used, just like the seismic recording of an explosion, in tomography, monitoring, etc. I will describe a physical acoustics experiment designed to prove the validity of this approach, and illustrate the application of this concept to imaging of the Earth's lithosphere under the Alpine mountain range.