This project supports an extended visit to the U.S. by a recent PhD who is the sole (world-wide) expert at experiments with random ultrasonic and seismic waves in the context of new "mesoscopic" theories for such waves. These theories, first developed in the ultrasonics lab at Illinois, are particularly important for earth sciences in that they imply new methods for seismic signal processing with which new information on the structure of the earth's crust could be extracted. This researcher's presence at Illinois will facilitate cross fertilization between diffuse field ultrasonics researchers and seismologists and it will accelerate the US experimental and theoretical effort on such waves.
Researchers will construct scale models of the earth and the earth's crust and conduct ultrasonic experiments on them in order to test these theories. Contrary to intuition perhaps, random wave fields (such as are found in ambient seismic noise or in the long ringing seismic coda that follows earthquakes) contain much useful information on the medium in which they propagate. In principle they contain all information which is normally obtained at great expense and inconvenience in seismology and exploration geophysics by use of explosives and "thumpers," or with no control by use of direct waves from earthquakes. This project will elucidate the limits and potential of this promising new approach for obtaining information on the earth. --
