Onlap is a particular pattern of reflections in seismic data that, according to principles of sequence stratigraphy, occurs during periods of transgression.
在地震资料中，上超是一种特殊式样的反射，依照层序地层学的原理，它出现在海侵作用期间。
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On the seismic section it appears as erosion, toplap, onlap, downlap;