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Imaging shallow objects with scattered guided waves

Current surface seismic reflection techniques based on the common-midpoint (CMP) reflection stacking method cannot be readily used to image small objects in the first few meters of a weathered layer. We discuss a seismic imaging method to detect such objects; it uses the first-arrival (guided) wave, scattered by shallow heterogeneities and converted into scattered Rayleigh waves. These guided waves and Rayleigh waves are dominant in the shallow weathered layer and therefore might be suitable for shallow object imaging. We applied this method to a field data set and found that we could certainly image meter-size objects up to about 3 m off to the side of a survey line consisting of vertical geophones. There are indications that cross-line horizontal geophone data could be used to identify shallow objects up to 10 m offline in the same region.