To the uninitiated the challenge may seem mind-boggling: When a seismic wave is emitted at the earth's surface and reflected by a deep target, it typically generates a displacement in the order of a few Angstroms (10−10 meters) on its return to the earth's surface. How can we seriously expect the geophone—a rather crude contraption involving a magnet and a moving coil inside a plastic jug mounted on a spike, stomped into the ground by a restless doodlebugger—to be sensitive to such infinitesimal displacements? To complicate matters, noise—whether ambient or source-generated—induces displacements of up to a millimeter (107...

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