The scattering of a symmetric pair of plane waves by a crack in an isotropic, homogeneous, linearly elastic solid is considered. For high frequency, an asymptotic solution to the integral equation for the normal crack-opening displacement (COD) is found. The elliptical and penny-shaped cracks are considered in some detail. For the penny-shaped crack, excellent agreement with numerical results is found as well as agreement with other asymptotic results.