Artifacts Arising From Symmetries in Seismic Data

Dr. Cliff Nolan (University of Limerick)

Frank Adams 2,

Consider seismic waves emitted on the earth’s surface.  Such waves travel into the subsurface where they may scatter from interfaces between different materials and then return to the surface again to be recorded by recording instruments known as geophones.  Commonly, a single seismic source (of energy) is used and an array of geophones records the scattered waves.  It is has been know for years that if the subsurface is strongly refracting, then multi-pathing of the scattered waves leads to artifacts in a seismic image of the subsurface.  These artifacts do not appear when the subsurfaces do not strongly refract waves.   In this talk, we consider another type of data set, known as ``Common Midpoint’’ data where each seismic source and geophone are symmetrically placed about a line on the earth’s surface.  We show how these artifacts reappear, even in a subsurface that has constant propagation speed (and hence no refraction takes place).  We use the framework of microlocal analysis to show how this happens and furthermore, we quantify the strength of the artifacts, showing that they are just as strong as bona-fida images of interfaces.  The technical tool that plays the central role in this analysis is that of Paired-Lagrangian distributions

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