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Kansas Geological Survey, Open-file Report 2005-4

MASW--Horizontal resolution of 2D shear-velocity (Vs) mapping

by Choon B. Park

KGS Open-file Report 2005-4
Feb. 17, 2005


An MASW survey to produce a 2-D (surface and depth) shear-wave velocity (Vs) map involves the acquisition of multiple records (of twelve or more channels) with the same source-receiver configuration moved successively by a fixed distance interval (a few to several stations) along a linear survey line. Acquired records then go through the dispersion-inversion processing to produce a 1-D (depth) Vs profile for each record by treating the subsurface distance spanned by one receiver spread as the horizontallylayered earth model. All these 1-D profiles are then assembled according to the surface coordinate at the midpoint of the spread used to acquire the corresponding record and then the final 2-D map is constructed by using a spatial interpolation scheme. The horizontal resolution of the map is therefore most influenced by two field parameters: the receiver spread length and the acquisition interval. The receiver spread length sets the theoretical lower limit and any Vs structure with its lateral dimension smaller than this will not be properly resolved in the final Vs map. An acquisition interval smaller than the spread length will not improve this limitation as spatial smearing has already been introduced by the receiver spread. However, since all 1-D Vs profiles will always contain some error resulting from the imperfect analysis in dispersion-inversion processing, processing accuracy can also influence the resolution. In this sense, a smaller acquisition interval will improve the resolution through the statistical principle as it provides a greater redundancy in measurement at the expense of survey cost. The role of these controls is described based on the numerical simulations.

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Kansas Geological Survey, Geophysics
Placed online Feb. 10, 2006
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