Introduction

Subsurface images provided by the seismic reflection method are the single most important tool used in oil and gas exploration. Almost exclusively, our conceptual model of the seismic reflection method, and consequently our seismic data processing algorithms, treat primary reflections, those waves that are scattered back towards the surface only once, as the ``signal''. The traveltimes of the primary reflections are used to map the structure of lithology contrasts while their amplitudes provide information about the magnitude of the lithology contrasts as well as other information such as presence or absence of fluids in the pore spaces of the rock. All other waves such as multiples, waves that are scattered back toward the surface more than once, are considered ``noise''.