Perhaps the most costly subsurface mapping errors made by industry today are to use throw instead of vertical separation to contour across faults. Indeed the two terms are often confused or used interchangeably, i.e. vertical separation is often called throw and throw is substituted for vertical separation. These two terms are, however, not the same and are a measure of two distinctly different geometric properties. In this talk, we demonstrate that to contour throw across faults (normal or reverse) instead of vertical separation can typically (commonly) result in mapping errors on the order of 25% or greater. New equations have been derived and nomograms generated which provide quantitative guidelines to construct structure maps in faulted areas. We define the fault components applicable to subsurface mapping, present the quantitative relationship of vertical separation to throw, introduce the correct technique to contour vertical separation across a fault (using seismic data and well logs), and discuss the analysis of errors caused by mapping throw in place of vertical separation.

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