The reflection seismic method is the most frequently used exploration method for imaging and monitoring subsurface structures with high resolution. It has proven its qualities from the scale of regional seismology to the scale of near-surface applications that look just a few meters below the surface. The reflection method uses controlled active sources at known positions to give rise to reflections recorded at known receiver positions. The reflections’ two-wave travel time is used to extract desired information about and image the subsurface structures. When active sources are unavailable or undesired, one can retrieve body-wave reflections from application of seismic interferometry (SI) to sources of opportunity—quakes, tremors, ambient noise, or even man-made sources not connected to the exploration campaign. We show examples of imaging of subsurface structures using reflections retrieved from quakes and ambient noise. We apply SI by autocorrelation to global earthquake to image seismic and aseismic parts of the Nazca plate and the Moho at these places, SI by multidimensional deconvolution to P-wave coda from local earthquakes to image the Moho and the crust at the same places, and SI by autocorrelation to deep moonquakes to image the lunar Moho and to ambient noise to monitor CO2 sequestration. @en

By cross-correlating recordings of ambient seismic noise, one can retrieve the subsurface reflection response. The quality of the retrieved reflections would depend on the qualities of the ambient noise. In a previous study, we cross-correlated ambient-noise data recorded in a desert area in North Africa and showed that we retrieved reflections. This was done assuming that body-wave noise continuously illuminates the recording array. But this is not necessarily true - noise which carries body-wave information can be present only at certain times. We now use only parts of the recorded noise during the correlation process. These parts contain identifiable body-wave events. We show that the results, retrieved only from the noise containing the events, exhibit clearer reflection arrivals.

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One of the applications of seismic interferometry (SI) by cross-correlation is the retrieval of the reflection response of the subsurface from ambient seismic noise recorded at the surface. We apply SI to ambient-noise data recorded in a desert area in North Africa. The retrieved results show distinct coherent events with hyperbolic moveout. We compare the retrieved results with results from an active reflection survey recorded at the same location. We apply standard seismic processing to the retrieved results and obtain a stacked time-migrated reflection profile of the subsurface.@en